// SPDX-License-Identifier: GPL-2.0
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/* kernel/rwsem.c: R/W semaphores, public implementation
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*
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* Written by David Howells (dhowells@redhat.com).
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* Derived from asm-i386/semaphore.h
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*
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* Writer lock-stealing by Alex Shi <alex.shi@intel.com>
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* and Michel Lespinasse <walken@google.com>
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*
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* Optimistic spinning by Tim Chen <tim.c.chen@intel.com>
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* and Davidlohr Bueso <davidlohr@hp.com>. Based on mutexes.
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*
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* Rwsem count bit fields re-definition and rwsem rearchitecture by
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* Waiman Long <longman@redhat.com> and
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* Peter Zijlstra <peterz@infradead.org>.
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*/
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#include <linux/types.h>
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#include <linux/kernel.h>
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#include <linux/sched.h>
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#include <linux/sched/rt.h>
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#include <linux/sched/task.h>
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#include <linux/sched/debug.h>
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#include <linux/sched/wake_q.h>
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#include <linux/sched/signal.h>
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#include <linux/sched/clock.h>
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#include <linux/export.h>
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#include <linux/rwsem.h>
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#include <linux/atomic.h>
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#ifndef CONFIG_PREEMPT_RT
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#include "lock_events.h"
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#include <trace/hooks/rwsem.h>
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#include <trace/hooks/dtask.h>
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/*
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* The least significant 3 bits of the owner value has the following
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* meanings when set.
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* - Bit 0: RWSEM_READER_OWNED - The rwsem is owned by readers
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* - Bit 1: RWSEM_RD_NONSPINNABLE - Readers cannot spin on this lock.
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* - Bit 2: RWSEM_WR_NONSPINNABLE - Writers cannot spin on this lock.
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*
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* When the rwsem is either owned by an anonymous writer, or it is
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* reader-owned, but a spinning writer has timed out, both nonspinnable
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* bits will be set to disable optimistic spinning by readers and writers.
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* In the later case, the last unlocking reader should then check the
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* writer nonspinnable bit and clear it only to give writers preference
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* to acquire the lock via optimistic spinning, but not readers. Similar
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* action is also done in the reader slowpath.
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* When a writer acquires a rwsem, it puts its task_struct pointer
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* into the owner field. It is cleared after an unlock.
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*
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* When a reader acquires a rwsem, it will also puts its task_struct
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* pointer into the owner field with the RWSEM_READER_OWNED bit set.
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* On unlock, the owner field will largely be left untouched. So
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* for a free or reader-owned rwsem, the owner value may contain
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* information about the last reader that acquires the rwsem.
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*
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* That information may be helpful in debugging cases where the system
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* seems to hang on a reader owned rwsem especially if only one reader
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* is involved. Ideally we would like to track all the readers that own
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* a rwsem, but the overhead is simply too big.
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*
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* Reader optimistic spinning is helpful when the reader critical section
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* is short and there aren't that many readers around. It makes readers
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* relatively more preferred than writers. When a writer times out spinning
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* on a reader-owned lock and set the nospinnable bits, there are two main
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* reasons for that.
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*
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* 1) The reader critical section is long, perhaps the task sleeps after
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* acquiring the read lock.
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* 2) There are just too many readers contending the lock causing it to
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* take a while to service all of them.
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*
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* In the former case, long reader critical section will impede the progress
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* of writers which is usually more important for system performance. In
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* the later case, reader optimistic spinning tends to make the reader
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* groups that contain readers that acquire the lock together smaller
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* leading to more of them. That may hurt performance in some cases. In
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* other words, the setting of nonspinnable bits indicates that reader
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* optimistic spinning may not be helpful for those workloads that cause
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* it.
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*
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* Therefore, any writers that had observed the setting of the writer
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* nonspinnable bit for a given rwsem after they fail to acquire the lock
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* via optimistic spinning will set the reader nonspinnable bit once they
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* acquire the write lock. Similarly, readers that observe the setting
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* of reader nonspinnable bit at slowpath entry will set the reader
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* nonspinnable bits when they acquire the read lock via the wakeup path.
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*
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* Once the reader nonspinnable bit is on, it will only be reset when
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* a writer is able to acquire the rwsem in the fast path or somehow a
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* reader or writer in the slowpath doesn't observe the nonspinable bit.
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*
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* This is to discourage reader optmistic spinning on that particular
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* rwsem and make writers more preferred. This adaptive disabling of reader
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* optimistic spinning will alleviate the negative side effect of this
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* feature.
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*/
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#define RWSEM_READER_OWNED (1UL << 0)
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#define RWSEM_RD_NONSPINNABLE (1UL << 1)
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#define RWSEM_WR_NONSPINNABLE (1UL << 2)
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#define RWSEM_NONSPINNABLE (RWSEM_RD_NONSPINNABLE | RWSEM_WR_NONSPINNABLE)
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#define RWSEM_OWNER_FLAGS_MASK (RWSEM_READER_OWNED | RWSEM_NONSPINNABLE)
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#ifdef CONFIG_DEBUG_RWSEMS
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# define DEBUG_RWSEMS_WARN_ON(c, sem) do { \
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if (!debug_locks_silent && \
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WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, magic = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
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#c, atomic_long_read(&(sem)->count), \
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(unsigned long) sem->magic, \
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atomic_long_read(&(sem)->owner), (long)current, \
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list_empty(&(sem)->wait_list) ? "" : "not ")) \
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debug_locks_off(); \
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} while (0)
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#else
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# define DEBUG_RWSEMS_WARN_ON(c, sem)
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#endif
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/*
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* On 64-bit architectures, the bit definitions of the count are:
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*
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* Bit 0 - writer locked bit
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* Bit 1 - waiters present bit
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* Bit 2 - lock handoff bit
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* Bits 3-7 - reserved
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* Bits 8-62 - 55-bit reader count
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* Bit 63 - read fail bit
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*
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* On 32-bit architectures, the bit definitions of the count are:
|
*
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* Bit 0 - writer locked bit
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* Bit 1 - waiters present bit
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* Bit 2 - lock handoff bit
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* Bits 3-7 - reserved
|
* Bits 8-30 - 23-bit reader count
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* Bit 31 - read fail bit
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*
|
* It is not likely that the most significant bit (read fail bit) will ever
|
* be set. This guard bit is still checked anyway in the down_read() fastpath
|
* just in case we need to use up more of the reader bits for other purpose
|
* in the future.
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*
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* atomic_long_fetch_add() is used to obtain reader lock, whereas
|
* atomic_long_cmpxchg() will be used to obtain writer lock.
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*
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* There are three places where the lock handoff bit may be set or cleared.
|
* 1) rwsem_mark_wake() for readers.
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* 2) rwsem_try_write_lock() for writers.
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* 3) Error path of rwsem_down_write_slowpath().
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*
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* For all the above cases, wait_lock will be held. A writer must also
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* be the first one in the wait_list to be eligible for setting the handoff
|
* bit. So concurrent setting/clearing of handoff bit is not possible.
|
*/
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#define RWSEM_WRITER_LOCKED (1UL << 0)
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#define RWSEM_FLAG_WAITERS (1UL << 1)
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#define RWSEM_FLAG_HANDOFF (1UL << 2)
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#define RWSEM_FLAG_READFAIL (1UL << (BITS_PER_LONG - 1))
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#define RWSEM_READER_SHIFT 8
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#define RWSEM_READER_BIAS (1UL << RWSEM_READER_SHIFT)
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#define RWSEM_READER_MASK (~(RWSEM_READER_BIAS - 1))
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#define RWSEM_WRITER_MASK RWSEM_WRITER_LOCKED
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#define RWSEM_LOCK_MASK (RWSEM_WRITER_MASK|RWSEM_READER_MASK)
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#define RWSEM_READ_FAILED_MASK (RWSEM_WRITER_MASK|RWSEM_FLAG_WAITERS|\
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RWSEM_FLAG_HANDOFF|RWSEM_FLAG_READFAIL)
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/*
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* All writes to owner are protected by WRITE_ONCE() to make sure that
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* store tearing can't happen as optimistic spinners may read and use
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* the owner value concurrently without lock. Read from owner, however,
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* may not need READ_ONCE() as long as the pointer value is only used
|
* for comparison and isn't being dereferenced.
|
*/
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static inline void rwsem_set_owner(struct rw_semaphore *sem)
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{
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atomic_long_set(&sem->owner, (long)current);
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trace_android_vh_rwsem_set_owner(sem);
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}
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static inline void rwsem_clear_owner(struct rw_semaphore *sem)
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{
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atomic_long_set(&sem->owner, 0);
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}
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/*
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* Test the flags in the owner field.
|
*/
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static inline bool rwsem_test_oflags(struct rw_semaphore *sem, long flags)
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{
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return atomic_long_read(&sem->owner) & flags;
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}
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/*
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* The task_struct pointer of the last owning reader will be left in
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* the owner field.
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*
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* Note that the owner value just indicates the task has owned the rwsem
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* previously, it may not be the real owner or one of the real owners
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* anymore when that field is examined, so take it with a grain of salt.
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*
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* The reader non-spinnable bit is preserved.
|
*/
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static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
|
struct task_struct *owner)
|
{
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unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED |
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(atomic_long_read(&sem->owner) & RWSEM_RD_NONSPINNABLE);
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|
atomic_long_set(&sem->owner, val);
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}
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static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
|
{
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__rwsem_set_reader_owned(sem, current);
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trace_android_vh_rwsem_set_reader_owned(sem);
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}
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/*
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* Return true if the rwsem is owned by a reader.
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*/
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static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
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{
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#ifdef CONFIG_DEBUG_RWSEMS
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/*
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* Check the count to see if it is write-locked.
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*/
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long count = atomic_long_read(&sem->count);
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if (count & RWSEM_WRITER_MASK)
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return false;
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#endif
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return rwsem_test_oflags(sem, RWSEM_READER_OWNED);
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}
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#ifdef CONFIG_DEBUG_RWSEMS
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/*
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* With CONFIG_DEBUG_RWSEMS configured, it will make sure that if there
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* is a task pointer in owner of a reader-owned rwsem, it will be the
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* real owner or one of the real owners. The only exception is when the
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* unlock is done by up_read_non_owner().
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*/
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static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
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{
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unsigned long val = atomic_long_read(&sem->owner);
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while ((val & ~RWSEM_OWNER_FLAGS_MASK) == (unsigned long)current) {
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if (atomic_long_try_cmpxchg(&sem->owner, &val,
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val & RWSEM_OWNER_FLAGS_MASK))
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return;
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}
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}
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#else
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static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
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{
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}
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#endif
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/*
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* Set the RWSEM_NONSPINNABLE bits if the RWSEM_READER_OWNED flag
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* remains set. Otherwise, the operation will be aborted.
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*/
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static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
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{
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unsigned long owner = atomic_long_read(&sem->owner);
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do {
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if (!(owner & RWSEM_READER_OWNED))
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break;
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if (owner & RWSEM_NONSPINNABLE)
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break;
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} while (!atomic_long_try_cmpxchg(&sem->owner, &owner,
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owner | RWSEM_NONSPINNABLE));
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}
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static inline bool rwsem_read_trylock(struct rw_semaphore *sem)
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{
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long cnt = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
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if (WARN_ON_ONCE(cnt < 0))
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rwsem_set_nonspinnable(sem);
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if ((cnt & RWSEM_READ_FAILED_MASK) == 0)
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trace_android_vh_record_rwsem_lock_starttime(current, jiffies);
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return !(cnt & RWSEM_READ_FAILED_MASK);
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}
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/*
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* Return just the real task structure pointer of the owner
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*/
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static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
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{
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return (struct task_struct *)
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(atomic_long_read(&sem->owner) & ~RWSEM_OWNER_FLAGS_MASK);
|
}
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/*
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* Return the real task structure pointer of the owner and the embedded
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* flags in the owner. pflags must be non-NULL.
|
*/
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static inline struct task_struct *
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rwsem_owner_flags(struct rw_semaphore *sem, unsigned long *pflags)
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{
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unsigned long owner = atomic_long_read(&sem->owner);
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|
*pflags = owner & RWSEM_OWNER_FLAGS_MASK;
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return (struct task_struct *)(owner & ~RWSEM_OWNER_FLAGS_MASK);
|
}
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/*
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* Guide to the rw_semaphore's count field.
|
*
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* When the RWSEM_WRITER_LOCKED bit in count is set, the lock is owned
|
* by a writer.
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*
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* The lock is owned by readers when
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* (1) the RWSEM_WRITER_LOCKED isn't set in count,
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* (2) some of the reader bits are set in count, and
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* (3) the owner field has RWSEM_READ_OWNED bit set.
|
*
|
* Having some reader bits set is not enough to guarantee a readers owned
|
* lock as the readers may be in the process of backing out from the count
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* and a writer has just released the lock. So another writer may steal
|
* the lock immediately after that.
|
*/
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/*
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* Initialize an rwsem:
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*/
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void __init_rwsem(struct rw_semaphore *sem, const char *name,
|
struct lock_class_key *key)
|
{
|
#ifdef CONFIG_DEBUG_LOCK_ALLOC
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/*
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* Make sure we are not reinitializing a held semaphore:
|
*/
|
debug_check_no_locks_freed((void *)sem, sizeof(*sem));
|
lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
|
#endif
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#ifdef CONFIG_DEBUG_RWSEMS
|
sem->magic = sem;
|
#endif
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atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
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raw_spin_lock_init(&sem->wait_lock);
|
INIT_LIST_HEAD(&sem->wait_list);
|
atomic_long_set(&sem->owner, 0L);
|
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
|
osq_lock_init(&sem->osq);
|
#endif
|
trace_android_vh_rwsem_init(sem);
|
}
|
EXPORT_SYMBOL(__init_rwsem);
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|
#define rwsem_first_waiter(sem) \
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list_first_entry(&sem->wait_list, struct rwsem_waiter, list)
|
|
enum rwsem_wake_type {
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RWSEM_WAKE_ANY, /* Wake whatever's at head of wait list */
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RWSEM_WAKE_READERS, /* Wake readers only */
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RWSEM_WAKE_READ_OWNED /* Waker thread holds the read lock */
|
};
|
|
enum writer_wait_state {
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WRITER_NOT_FIRST, /* Writer is not first in wait list */
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WRITER_FIRST, /* Writer is first in wait list */
|
WRITER_HANDOFF /* Writer is first & handoff needed */
|
};
|
|
/*
|
* The typical HZ value is either 250 or 1000. So set the minimum waiting
|
* time to at least 4ms or 1 jiffy (if it is higher than 4ms) in the wait
|
* queue before initiating the handoff protocol.
|
*/
|
#define RWSEM_WAIT_TIMEOUT DIV_ROUND_UP(HZ, 250)
|
|
/*
|
* Magic number to batch-wakeup waiting readers, even when writers are
|
* also present in the queue. This both limits the amount of work the
|
* waking thread must do and also prevents any potential counter overflow,
|
* however unlikely.
|
*/
|
#define MAX_READERS_WAKEUP 0x100
|
|
/*
|
* handle the lock release when processes blocked on it that can now run
|
* - if we come here from up_xxxx(), then the RWSEM_FLAG_WAITERS bit must
|
* have been set.
|
* - there must be someone on the queue
|
* - the wait_lock must be held by the caller
|
* - tasks are marked for wakeup, the caller must later invoke wake_up_q()
|
* to actually wakeup the blocked task(s) and drop the reference count,
|
* preferably when the wait_lock is released
|
* - woken process blocks are discarded from the list after having task zeroed
|
* - writers are only marked woken if downgrading is false
|
*/
|
static void rwsem_mark_wake(struct rw_semaphore *sem,
|
enum rwsem_wake_type wake_type,
|
struct wake_q_head *wake_q)
|
{
|
struct rwsem_waiter *waiter, *tmp;
|
long oldcount, woken = 0, adjustment = 0;
|
struct list_head wlist;
|
|
lockdep_assert_held(&sem->wait_lock);
|
|
/*
|
* Take a peek at the queue head waiter such that we can determine
|
* the wakeup(s) to perform.
|
*/
|
waiter = rwsem_first_waiter(sem);
|
|
if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
|
if (wake_type == RWSEM_WAKE_ANY) {
|
/*
|
* Mark writer at the front of the queue for wakeup.
|
* Until the task is actually later awoken later by
|
* the caller, other writers are able to steal it.
|
* Readers, on the other hand, will block as they
|
* will notice the queued writer.
|
*/
|
wake_q_add(wake_q, waiter->task);
|
lockevent_inc(rwsem_wake_writer);
|
}
|
|
return;
|
}
|
|
/*
|
* No reader wakeup if there are too many of them already.
|
*/
|
if (unlikely(atomic_long_read(&sem->count) < 0))
|
return;
|
|
/*
|
* Writers might steal the lock before we grant it to the next reader.
|
* We prefer to do the first reader grant before counting readers
|
* so we can bail out early if a writer stole the lock.
|
*/
|
if (wake_type != RWSEM_WAKE_READ_OWNED) {
|
struct task_struct *owner;
|
|
adjustment = RWSEM_READER_BIAS;
|
oldcount = atomic_long_fetch_add(adjustment, &sem->count);
|
if (unlikely(oldcount & RWSEM_WRITER_MASK)) {
|
/*
|
* When we've been waiting "too" long (for writers
|
* to give up the lock), request a HANDOFF to
|
* force the issue.
|
*/
|
if (!(oldcount & RWSEM_FLAG_HANDOFF) &&
|
time_after(jiffies, waiter->timeout)) {
|
adjustment -= RWSEM_FLAG_HANDOFF;
|
lockevent_inc(rwsem_rlock_handoff);
|
}
|
|
atomic_long_add(-adjustment, &sem->count);
|
return;
|
}
|
/*
|
* Set it to reader-owned to give spinners an early
|
* indication that readers now have the lock.
|
* The reader nonspinnable bit seen at slowpath entry of
|
* the reader is copied over.
|
*/
|
owner = waiter->task;
|
if (waiter->last_rowner & RWSEM_RD_NONSPINNABLE) {
|
owner = (void *)((unsigned long)owner | RWSEM_RD_NONSPINNABLE);
|
lockevent_inc(rwsem_opt_norspin);
|
}
|
__rwsem_set_reader_owned(sem, owner);
|
}
|
|
/*
|
* Grant up to MAX_READERS_WAKEUP read locks to all the readers in the
|
* queue. We know that the woken will be at least 1 as we accounted
|
* for above. Note we increment the 'active part' of the count by the
|
* number of readers before waking any processes up.
|
*
|
* This is an adaptation of the phase-fair R/W locks where at the
|
* reader phase (first waiter is a reader), all readers are eligible
|
* to acquire the lock at the same time irrespective of their order
|
* in the queue. The writers acquire the lock according to their
|
* order in the queue.
|
*
|
* We have to do wakeup in 2 passes to prevent the possibility that
|
* the reader count may be decremented before it is incremented. It
|
* is because the to-be-woken waiter may not have slept yet. So it
|
* may see waiter->task got cleared, finish its critical section and
|
* do an unlock before the reader count increment.
|
*
|
* 1) Collect the read-waiters in a separate list, count them and
|
* fully increment the reader count in rwsem.
|
* 2) For each waiters in the new list, clear waiter->task and
|
* put them into wake_q to be woken up later.
|
*/
|
INIT_LIST_HEAD(&wlist);
|
list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) {
|
if (waiter->type == RWSEM_WAITING_FOR_WRITE)
|
continue;
|
|
woken++;
|
list_move_tail(&waiter->list, &wlist);
|
|
trace_android_vh_rwsem_mark_wake_readers(sem, waiter);
|
/*
|
* Limit # of readers that can be woken up per wakeup call.
|
*/
|
if (woken >= MAX_READERS_WAKEUP)
|
break;
|
}
|
|
adjustment = woken * RWSEM_READER_BIAS - adjustment;
|
lockevent_cond_inc(rwsem_wake_reader, woken);
|
if (list_empty(&sem->wait_list)) {
|
/* hit end of list above */
|
adjustment -= RWSEM_FLAG_WAITERS;
|
}
|
|
/*
|
* When we've woken a reader, we no longer need to force writers
|
* to give up the lock and we can clear HANDOFF.
|
*/
|
if (woken && (atomic_long_read(&sem->count) & RWSEM_FLAG_HANDOFF))
|
adjustment -= RWSEM_FLAG_HANDOFF;
|
|
if (adjustment)
|
atomic_long_add(adjustment, &sem->count);
|
|
/* 2nd pass */
|
list_for_each_entry_safe(waiter, tmp, &wlist, list) {
|
struct task_struct *tsk;
|
|
tsk = waiter->task;
|
get_task_struct(tsk);
|
|
/*
|
* Ensure calling get_task_struct() before setting the reader
|
* waiter to nil such that rwsem_down_read_slowpath() cannot
|
* race with do_exit() by always holding a reference count
|
* to the task to wakeup.
|
*/
|
smp_store_release(&waiter->task, NULL);
|
/*
|
* Ensure issuing the wakeup (either by us or someone else)
|
* after setting the reader waiter to nil.
|
*/
|
wake_q_add_safe(wake_q, tsk);
|
}
|
}
|
|
/*
|
* This function must be called with the sem->wait_lock held to prevent
|
* race conditions between checking the rwsem wait list and setting the
|
* sem->count accordingly.
|
*
|
* If wstate is WRITER_HANDOFF, it will make sure that either the handoff
|
* bit is set or the lock is acquired with handoff bit cleared.
|
*/
|
static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
|
enum writer_wait_state wstate)
|
{
|
long count, new;
|
|
lockdep_assert_held(&sem->wait_lock);
|
|
count = atomic_long_read(&sem->count);
|
do {
|
bool has_handoff = !!(count & RWSEM_FLAG_HANDOFF);
|
|
if (has_handoff && wstate == WRITER_NOT_FIRST)
|
return false;
|
|
new = count;
|
|
if (count & RWSEM_LOCK_MASK) {
|
if (has_handoff || (wstate != WRITER_HANDOFF))
|
return false;
|
|
new |= RWSEM_FLAG_HANDOFF;
|
} else {
|
new |= RWSEM_WRITER_LOCKED;
|
new &= ~RWSEM_FLAG_HANDOFF;
|
|
if (list_is_singular(&sem->wait_list))
|
new &= ~RWSEM_FLAG_WAITERS;
|
}
|
} while (!atomic_long_try_cmpxchg_acquire(&sem->count, &count, new));
|
|
/*
|
* We have either acquired the lock with handoff bit cleared or
|
* set the handoff bit.
|
*/
|
if (new & RWSEM_FLAG_HANDOFF)
|
return false;
|
|
rwsem_set_owner(sem);
|
return true;
|
}
|
|
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
|
/*
|
* Try to acquire read lock before the reader is put on wait queue.
|
* Lock acquisition isn't allowed if the rwsem is locked or a writer handoff
|
* is ongoing.
|
*/
|
static inline bool rwsem_try_read_lock_unqueued(struct rw_semaphore *sem)
|
{
|
long count = atomic_long_read(&sem->count);
|
|
if (count & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))
|
return false;
|
|
count = atomic_long_fetch_add_acquire(RWSEM_READER_BIAS, &sem->count);
|
if (!(count & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
|
rwsem_set_reader_owned(sem);
|
lockevent_inc(rwsem_opt_rlock);
|
return true;
|
}
|
|
/* Back out the change */
|
atomic_long_add(-RWSEM_READER_BIAS, &sem->count);
|
return false;
|
}
|
|
/*
|
* Try to acquire write lock before the writer has been put on wait queue.
|
*/
|
static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
|
{
|
long count = atomic_long_read(&sem->count);
|
|
while (!(count & (RWSEM_LOCK_MASK|RWSEM_FLAG_HANDOFF))) {
|
if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
|
count | RWSEM_WRITER_LOCKED)) {
|
rwsem_set_owner(sem);
|
lockevent_inc(rwsem_opt_wlock);
|
return true;
|
}
|
}
|
return false;
|
}
|
|
static inline bool owner_on_cpu(struct task_struct *owner)
|
{
|
/*
|
* As lock holder preemption issue, we both skip spinning if
|
* task is not on cpu or its cpu is preempted
|
*/
|
return owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
|
}
|
|
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
|
unsigned long nonspinnable)
|
{
|
struct task_struct *owner;
|
unsigned long flags;
|
bool ret = true;
|
|
if (need_resched()) {
|
lockevent_inc(rwsem_opt_fail);
|
return false;
|
}
|
|
preempt_disable();
|
rcu_read_lock();
|
owner = rwsem_owner_flags(sem, &flags);
|
/*
|
* Don't check the read-owner as the entry may be stale.
|
*/
|
if ((flags & nonspinnable) ||
|
(owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner)))
|
ret = false;
|
rcu_read_unlock();
|
preempt_enable();
|
|
lockevent_cond_inc(rwsem_opt_fail, !ret);
|
return ret;
|
}
|
|
/*
|
* The rwsem_spin_on_owner() function returns the folowing 4 values
|
* depending on the lock owner state.
|
* OWNER_NULL : owner is currently NULL
|
* OWNER_WRITER: when owner changes and is a writer
|
* OWNER_READER: when owner changes and the new owner may be a reader.
|
* OWNER_NONSPINNABLE:
|
* when optimistic spinning has to stop because either the
|
* owner stops running, is unknown, or its timeslice has
|
* been used up.
|
*/
|
enum owner_state {
|
OWNER_NULL = 1 << 0,
|
OWNER_WRITER = 1 << 1,
|
OWNER_READER = 1 << 2,
|
OWNER_NONSPINNABLE = 1 << 3,
|
};
|
#define OWNER_SPINNABLE (OWNER_NULL | OWNER_WRITER | OWNER_READER)
|
|
static inline enum owner_state
|
rwsem_owner_state(struct task_struct *owner, unsigned long flags, unsigned long nonspinnable)
|
{
|
if (flags & nonspinnable)
|
return OWNER_NONSPINNABLE;
|
|
if (flags & RWSEM_READER_OWNED)
|
return OWNER_READER;
|
|
return owner ? OWNER_WRITER : OWNER_NULL;
|
}
|
|
static noinline enum owner_state
|
rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
|
{
|
struct task_struct *new, *owner;
|
unsigned long flags, new_flags;
|
enum owner_state state;
|
|
owner = rwsem_owner_flags(sem, &flags);
|
state = rwsem_owner_state(owner, flags, nonspinnable);
|
if (state != OWNER_WRITER)
|
return state;
|
|
rcu_read_lock();
|
for (;;) {
|
/*
|
* When a waiting writer set the handoff flag, it may spin
|
* on the owner as well. Once that writer acquires the lock,
|
* we can spin on it. So we don't need to quit even when the
|
* handoff bit is set.
|
*/
|
new = rwsem_owner_flags(sem, &new_flags);
|
if ((new != owner) || (new_flags != flags)) {
|
state = rwsem_owner_state(new, new_flags, nonspinnable);
|
break;
|
}
|
|
/*
|
* Ensure we emit the owner->on_cpu, dereference _after_
|
* checking sem->owner still matches owner, if that fails,
|
* owner might point to free()d memory, if it still matches,
|
* the rcu_read_lock() ensures the memory stays valid.
|
*/
|
barrier();
|
|
if (need_resched() || !owner_on_cpu(owner)) {
|
state = OWNER_NONSPINNABLE;
|
break;
|
}
|
|
cpu_relax();
|
}
|
rcu_read_unlock();
|
|
return state;
|
}
|
|
/*
|
* Calculate reader-owned rwsem spinning threshold for writer
|
*
|
* The more readers own the rwsem, the longer it will take for them to
|
* wind down and free the rwsem. So the empirical formula used to
|
* determine the actual spinning time limit here is:
|
*
|
* Spinning threshold = (10 + nr_readers/2)us
|
*
|
* The limit is capped to a maximum of 25us (30 readers). This is just
|
* a heuristic and is subjected to change in the future.
|
*/
|
static inline u64 rwsem_rspin_threshold(struct rw_semaphore *sem)
|
{
|
long count = atomic_long_read(&sem->count);
|
int readers = count >> RWSEM_READER_SHIFT;
|
u64 delta;
|
|
if (readers > 30)
|
readers = 30;
|
delta = (20 + readers) * NSEC_PER_USEC / 2;
|
|
return sched_clock() + delta;
|
}
|
|
static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
|
{
|
bool taken = false;
|
int prev_owner_state = OWNER_NULL;
|
int loop = 0;
|
u64 rspin_threshold = 0;
|
unsigned long nonspinnable = wlock ? RWSEM_WR_NONSPINNABLE
|
: RWSEM_RD_NONSPINNABLE;
|
|
preempt_disable();
|
|
/* sem->wait_lock should not be held when doing optimistic spinning */
|
if (!osq_lock(&sem->osq))
|
goto done;
|
|
/*
|
* Optimistically spin on the owner field and attempt to acquire the
|
* lock whenever the owner changes. Spinning will be stopped when:
|
* 1) the owning writer isn't running; or
|
* 2) readers own the lock and spinning time has exceeded limit.
|
*/
|
for (;;) {
|
enum owner_state owner_state;
|
|
owner_state = rwsem_spin_on_owner(sem, nonspinnable);
|
if (!(owner_state & OWNER_SPINNABLE))
|
break;
|
|
/*
|
* Try to acquire the lock
|
*/
|
taken = wlock ? rwsem_try_write_lock_unqueued(sem)
|
: rwsem_try_read_lock_unqueued(sem);
|
|
if (taken)
|
break;
|
|
/*
|
* Time-based reader-owned rwsem optimistic spinning
|
*/
|
if (wlock && (owner_state == OWNER_READER)) {
|
/*
|
* Re-initialize rspin_threshold every time when
|
* the owner state changes from non-reader to reader.
|
* This allows a writer to steal the lock in between
|
* 2 reader phases and have the threshold reset at
|
* the beginning of the 2nd reader phase.
|
*/
|
if (prev_owner_state != OWNER_READER) {
|
if (rwsem_test_oflags(sem, nonspinnable))
|
break;
|
rspin_threshold = rwsem_rspin_threshold(sem);
|
loop = 0;
|
}
|
|
/*
|
* Check time threshold once every 16 iterations to
|
* avoid calling sched_clock() too frequently so
|
* as to reduce the average latency between the times
|
* when the lock becomes free and when the spinner
|
* is ready to do a trylock.
|
*/
|
else if (!(++loop & 0xf) && (sched_clock() > rspin_threshold)) {
|
rwsem_set_nonspinnable(sem);
|
lockevent_inc(rwsem_opt_nospin);
|
break;
|
}
|
}
|
|
/*
|
* An RT task cannot do optimistic spinning if it cannot
|
* be sure the lock holder is running or live-lock may
|
* happen if the current task and the lock holder happen
|
* to run in the same CPU. However, aborting optimistic
|
* spinning while a NULL owner is detected may miss some
|
* opportunity where spinning can continue without causing
|
* problem.
|
*
|
* There are 2 possible cases where an RT task may be able
|
* to continue spinning.
|
*
|
* 1) The lock owner is in the process of releasing the
|
* lock, sem->owner is cleared but the lock has not
|
* been released yet.
|
* 2) The lock was free and owner cleared, but another
|
* task just comes in and acquire the lock before
|
* we try to get it. The new owner may be a spinnable
|
* writer.
|
*
|
* To take advantage of two scenarios listed agove, the RT
|
* task is made to retry one more time to see if it can
|
* acquire the lock or continue spinning on the new owning
|
* writer. Of course, if the time lag is long enough or the
|
* new owner is not a writer or spinnable, the RT task will
|
* quit spinning.
|
*
|
* If the owner is a writer, the need_resched() check is
|
* done inside rwsem_spin_on_owner(). If the owner is not
|
* a writer, need_resched() check needs to be done here.
|
*/
|
if (owner_state != OWNER_WRITER) {
|
if (need_resched())
|
break;
|
if (rt_task(current) &&
|
(prev_owner_state != OWNER_WRITER))
|
break;
|
}
|
prev_owner_state = owner_state;
|
|
/*
|
* The cpu_relax() call is a compiler barrier which forces
|
* everything in this loop to be re-loaded. We don't need
|
* memory barriers as we'll eventually observe the right
|
* values at the cost of a few extra spins.
|
*/
|
cpu_relax();
|
}
|
osq_unlock(&sem->osq);
|
done:
|
preempt_enable();
|
lockevent_cond_inc(rwsem_opt_fail, !taken);
|
return taken;
|
}
|
|
/*
|
* Clear the owner's RWSEM_WR_NONSPINNABLE bit if it is set. This should
|
* only be called when the reader count reaches 0.
|
*
|
* This give writers better chance to acquire the rwsem first before
|
* readers when the rwsem was being held by readers for a relatively long
|
* period of time. Race can happen that an optimistic spinner may have
|
* just stolen the rwsem and set the owner, but just clearing the
|
* RWSEM_WR_NONSPINNABLE bit will do no harm anyway.
|
*/
|
static inline void clear_wr_nonspinnable(struct rw_semaphore *sem)
|
{
|
if (rwsem_test_oflags(sem, RWSEM_WR_NONSPINNABLE))
|
atomic_long_andnot(RWSEM_WR_NONSPINNABLE, &sem->owner);
|
}
|
|
/*
|
* This function is called when the reader fails to acquire the lock via
|
* optimistic spinning. In this case we will still attempt to do a trylock
|
* when comparing the rwsem state right now with the state when entering
|
* the slowpath indicates that the reader is still in a valid reader phase.
|
* This happens when the following conditions are true:
|
*
|
* 1) The lock is currently reader owned, and
|
* 2) The lock is previously not reader-owned or the last read owner changes.
|
*
|
* In the former case, we have transitioned from a writer phase to a
|
* reader-phase while spinning. In the latter case, it means the reader
|
* phase hasn't ended when we entered the optimistic spinning loop. In
|
* both cases, the reader is eligible to acquire the lock. This is the
|
* secondary path where a read lock is acquired optimistically.
|
*
|
* The reader non-spinnable bit wasn't set at time of entry or it will
|
* not be here at all.
|
*/
|
static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
|
unsigned long last_rowner)
|
{
|
unsigned long owner = atomic_long_read(&sem->owner);
|
|
if (!(owner & RWSEM_READER_OWNED))
|
return false;
|
|
if (((owner ^ last_rowner) & ~RWSEM_OWNER_FLAGS_MASK) &&
|
rwsem_try_read_lock_unqueued(sem)) {
|
lockevent_inc(rwsem_opt_rlock2);
|
lockevent_add(rwsem_opt_fail, -1);
|
return true;
|
}
|
return false;
|
}
|
#else
|
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
|
unsigned long nonspinnable)
|
{
|
return false;
|
}
|
|
static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
|
{
|
return false;
|
}
|
|
static inline void clear_wr_nonspinnable(struct rw_semaphore *sem) { }
|
|
static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
|
unsigned long last_rowner)
|
{
|
return false;
|
}
|
|
static inline int
|
rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
|
{
|
return 0;
|
}
|
#define OWNER_NULL 1
|
#endif
|
|
/*
|
* Wait for the read lock to be granted
|
*/
|
static struct rw_semaphore __sched *
|
rwsem_down_read_slowpath(struct rw_semaphore *sem, int state)
|
{
|
long count, adjustment = -RWSEM_READER_BIAS;
|
struct rwsem_waiter waiter;
|
DEFINE_WAKE_Q(wake_q);
|
bool wake = false;
|
bool already_on_list = false;
|
|
/*
|
* Save the current read-owner of rwsem, if available, and the
|
* reader nonspinnable bit.
|
*/
|
waiter.last_rowner = atomic_long_read(&sem->owner);
|
if (!(waiter.last_rowner & RWSEM_READER_OWNED))
|
waiter.last_rowner &= RWSEM_RD_NONSPINNABLE;
|
|
if (!rwsem_can_spin_on_owner(sem, RWSEM_RD_NONSPINNABLE))
|
goto queue;
|
|
/*
|
* Undo read bias from down_read() and do optimistic spinning.
|
*/
|
atomic_long_add(-RWSEM_READER_BIAS, &sem->count);
|
adjustment = 0;
|
if (rwsem_optimistic_spin(sem, false)) {
|
/* rwsem_optimistic_spin() implies ACQUIRE on success */
|
/*
|
* Wake up other readers in the wait list if the front
|
* waiter is a reader.
|
*/
|
if ((atomic_long_read(&sem->count) & RWSEM_FLAG_WAITERS)) {
|
raw_spin_lock_irq(&sem->wait_lock);
|
if (!list_empty(&sem->wait_list))
|
rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED,
|
&wake_q);
|
raw_spin_unlock_irq(&sem->wait_lock);
|
wake_up_q(&wake_q);
|
}
|
trace_android_vh_record_rwsem_lock_starttime(current, jiffies);
|
return sem;
|
} else if (rwsem_reader_phase_trylock(sem, waiter.last_rowner)) {
|
/* rwsem_reader_phase_trylock() implies ACQUIRE on success */
|
trace_android_vh_record_rwsem_lock_starttime(current, jiffies);
|
return sem;
|
}
|
|
queue:
|
waiter.task = current;
|
waiter.type = RWSEM_WAITING_FOR_READ;
|
waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
|
|
raw_spin_lock_irq(&sem->wait_lock);
|
if (list_empty(&sem->wait_list)) {
|
/*
|
* In case the wait queue is empty and the lock isn't owned
|
* by a writer or has the handoff bit set, this reader can
|
* exit the slowpath and return immediately as its
|
* RWSEM_READER_BIAS has already been set in the count.
|
*/
|
if (adjustment && !(atomic_long_read(&sem->count) &
|
(RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
|
/* Provide lock ACQUIRE */
|
smp_acquire__after_ctrl_dep();
|
raw_spin_unlock_irq(&sem->wait_lock);
|
rwsem_set_reader_owned(sem);
|
lockevent_inc(rwsem_rlock_fast);
|
return sem;
|
}
|
adjustment += RWSEM_FLAG_WAITERS;
|
}
|
trace_android_vh_alter_rwsem_list_add(
|
&waiter,
|
sem, &already_on_list);
|
if (!already_on_list)
|
list_add_tail(&waiter.list, &sem->wait_list);
|
|
/* we're now waiting on the lock, but no longer actively locking */
|
if (adjustment)
|
count = atomic_long_add_return(adjustment, &sem->count);
|
else
|
count = atomic_long_read(&sem->count);
|
|
/*
|
* If there are no active locks, wake the front queued process(es).
|
*
|
* If there are no writers and we are first in the queue,
|
* wake our own waiter to join the existing active readers !
|
*/
|
if (!(count & RWSEM_LOCK_MASK)) {
|
clear_wr_nonspinnable(sem);
|
wake = true;
|
}
|
if (wake || (!(count & RWSEM_WRITER_MASK) &&
|
(adjustment & RWSEM_FLAG_WAITERS)))
|
rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
|
|
trace_android_vh_rwsem_wake(sem);
|
raw_spin_unlock_irq(&sem->wait_lock);
|
wake_up_q(&wake_q);
|
|
/* wait to be given the lock */
|
trace_android_vh_rwsem_read_wait_start(sem);
|
for (;;) {
|
set_current_state(state);
|
if (!smp_load_acquire(&waiter.task)) {
|
/* Matches rwsem_mark_wake()'s smp_store_release(). */
|
break;
|
}
|
if (signal_pending_state(state, current)) {
|
raw_spin_lock_irq(&sem->wait_lock);
|
if (waiter.task)
|
goto out_nolock;
|
raw_spin_unlock_irq(&sem->wait_lock);
|
/* Ordered by sem->wait_lock against rwsem_mark_wake(). */
|
break;
|
}
|
schedule();
|
lockevent_inc(rwsem_sleep_reader);
|
}
|
|
__set_current_state(TASK_RUNNING);
|
trace_android_vh_rwsem_read_wait_finish(sem);
|
lockevent_inc(rwsem_rlock);
|
trace_android_vh_record_rwsem_lock_starttime(current, jiffies);
|
return sem;
|
|
out_nolock:
|
list_del(&waiter.list);
|
if (list_empty(&sem->wait_list)) {
|
atomic_long_andnot(RWSEM_FLAG_WAITERS|RWSEM_FLAG_HANDOFF,
|
&sem->count);
|
}
|
raw_spin_unlock_irq(&sem->wait_lock);
|
__set_current_state(TASK_RUNNING);
|
trace_android_vh_rwsem_read_wait_finish(sem);
|
lockevent_inc(rwsem_rlock_fail);
|
return ERR_PTR(-EINTR);
|
}
|
|
/*
|
* This function is called by the a write lock owner. So the owner value
|
* won't get changed by others.
|
*/
|
static inline void rwsem_disable_reader_optspin(struct rw_semaphore *sem,
|
bool disable)
|
{
|
if (unlikely(disable)) {
|
atomic_long_or(RWSEM_RD_NONSPINNABLE, &sem->owner);
|
lockevent_inc(rwsem_opt_norspin);
|
}
|
}
|
|
/*
|
* Wait until we successfully acquire the write lock
|
*/
|
static struct rw_semaphore *
|
rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
|
{
|
long count;
|
bool disable_rspin;
|
enum writer_wait_state wstate;
|
struct rwsem_waiter waiter;
|
struct rw_semaphore *ret = sem;
|
DEFINE_WAKE_Q(wake_q);
|
bool already_on_list = false;
|
|
/* do optimistic spinning and steal lock if possible */
|
if (rwsem_can_spin_on_owner(sem, RWSEM_WR_NONSPINNABLE) &&
|
rwsem_optimistic_spin(sem, true)) {
|
/* rwsem_optimistic_spin() implies ACQUIRE on success */
|
trace_android_vh_record_rwsem_lock_starttime(current, jiffies);
|
return sem;
|
}
|
|
/*
|
* Disable reader optimistic spinning for this rwsem after
|
* acquiring the write lock when the setting of the nonspinnable
|
* bits are observed.
|
*/
|
disable_rspin = atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE;
|
|
/*
|
* Optimistic spinning failed, proceed to the slowpath
|
* and block until we can acquire the sem.
|
*/
|
waiter.task = current;
|
waiter.type = RWSEM_WAITING_FOR_WRITE;
|
waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
|
|
raw_spin_lock_irq(&sem->wait_lock);
|
|
/* account for this before adding a new element to the list */
|
wstate = list_empty(&sem->wait_list) ? WRITER_FIRST : WRITER_NOT_FIRST;
|
|
trace_android_vh_alter_rwsem_list_add(
|
&waiter,
|
sem, &already_on_list);
|
if (!already_on_list)
|
list_add_tail(&waiter.list, &sem->wait_list);
|
|
/* we're now waiting on the lock */
|
if (wstate == WRITER_NOT_FIRST) {
|
count = atomic_long_read(&sem->count);
|
|
/*
|
* If there were already threads queued before us and:
|
* 1) there are no active locks, wake the front
|
* queued process(es) as the handoff bit might be set.
|
* 2) there are no active writers and some readers, the lock
|
* must be read owned; so we try to wake any read lock
|
* waiters that were queued ahead of us.
|
*/
|
if (count & RWSEM_WRITER_MASK)
|
goto wait;
|
|
rwsem_mark_wake(sem, (count & RWSEM_READER_MASK)
|
? RWSEM_WAKE_READERS
|
: RWSEM_WAKE_ANY, &wake_q);
|
|
if (!wake_q_empty(&wake_q)) {
|
/*
|
* We want to minimize wait_lock hold time especially
|
* when a large number of readers are to be woken up.
|
*/
|
raw_spin_unlock_irq(&sem->wait_lock);
|
wake_up_q(&wake_q);
|
wake_q_init(&wake_q); /* Used again, reinit */
|
raw_spin_lock_irq(&sem->wait_lock);
|
}
|
} else {
|
atomic_long_or(RWSEM_FLAG_WAITERS, &sem->count);
|
}
|
|
wait:
|
trace_android_vh_rwsem_wake(sem);
|
/* wait until we successfully acquire the lock */
|
trace_android_vh_rwsem_write_wait_start(sem);
|
set_current_state(state);
|
for (;;) {
|
if (rwsem_try_write_lock(sem, wstate)) {
|
/* rwsem_try_write_lock() implies ACQUIRE on success */
|
break;
|
}
|
|
raw_spin_unlock_irq(&sem->wait_lock);
|
|
/*
|
* After setting the handoff bit and failing to acquire
|
* the lock, attempt to spin on owner to accelerate lock
|
* transfer. If the previous owner is a on-cpu writer and it
|
* has just released the lock, OWNER_NULL will be returned.
|
* In this case, we attempt to acquire the lock again
|
* without sleeping.
|
*/
|
if (wstate == WRITER_HANDOFF &&
|
rwsem_spin_on_owner(sem, RWSEM_NONSPINNABLE) == OWNER_NULL)
|
goto trylock_again;
|
|
/* Block until there are no active lockers. */
|
for (;;) {
|
if (signal_pending_state(state, current))
|
goto out_nolock;
|
|
schedule();
|
lockevent_inc(rwsem_sleep_writer);
|
set_current_state(state);
|
/*
|
* If HANDOFF bit is set, unconditionally do
|
* a trylock.
|
*/
|
if (wstate == WRITER_HANDOFF)
|
break;
|
|
if ((wstate == WRITER_NOT_FIRST) &&
|
(rwsem_first_waiter(sem) == &waiter))
|
wstate = WRITER_FIRST;
|
|
count = atomic_long_read(&sem->count);
|
if (!(count & RWSEM_LOCK_MASK))
|
break;
|
|
/*
|
* The setting of the handoff bit is deferred
|
* until rwsem_try_write_lock() is called.
|
*/
|
if ((wstate == WRITER_FIRST) && (rt_task(current) ||
|
time_after(jiffies, waiter.timeout))) {
|
wstate = WRITER_HANDOFF;
|
lockevent_inc(rwsem_wlock_handoff);
|
break;
|
}
|
}
|
trylock_again:
|
raw_spin_lock_irq(&sem->wait_lock);
|
}
|
__set_current_state(TASK_RUNNING);
|
trace_android_vh_rwsem_write_wait_finish(sem);
|
list_del(&waiter.list);
|
rwsem_disable_reader_optspin(sem, disable_rspin);
|
raw_spin_unlock_irq(&sem->wait_lock);
|
lockevent_inc(rwsem_wlock);
|
trace_android_vh_record_rwsem_lock_starttime(current, jiffies);
|
return ret;
|
|
out_nolock:
|
__set_current_state(TASK_RUNNING);
|
trace_android_vh_rwsem_write_wait_finish(sem);
|
raw_spin_lock_irq(&sem->wait_lock);
|
list_del(&waiter.list);
|
|
if (unlikely(wstate == WRITER_HANDOFF))
|
atomic_long_andnot(RWSEM_FLAG_HANDOFF, &sem->count);
|
|
if (list_empty(&sem->wait_list))
|
atomic_long_andnot(RWSEM_FLAG_WAITERS, &sem->count);
|
else
|
rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
|
raw_spin_unlock_irq(&sem->wait_lock);
|
wake_up_q(&wake_q);
|
lockevent_inc(rwsem_wlock_fail);
|
|
return ERR_PTR(-EINTR);
|
}
|
|
/*
|
* handle waking up a waiter on the semaphore
|
* - up_read/up_write has decremented the active part of count if we come here
|
*/
|
static struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem, long count)
|
{
|
unsigned long flags;
|
DEFINE_WAKE_Q(wake_q);
|
|
raw_spin_lock_irqsave(&sem->wait_lock, flags);
|
|
if (!list_empty(&sem->wait_list))
|
rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
|
trace_android_vh_rwsem_wake_finish(sem);
|
|
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
|
wake_up_q(&wake_q);
|
|
return sem;
|
}
|
|
/*
|
* downgrade a write lock into a read lock
|
* - caller incremented waiting part of count and discovered it still negative
|
* - just wake up any readers at the front of the queue
|
*/
|
static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
|
{
|
unsigned long flags;
|
DEFINE_WAKE_Q(wake_q);
|
|
raw_spin_lock_irqsave(&sem->wait_lock, flags);
|
|
if (!list_empty(&sem->wait_list))
|
rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);
|
|
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
|
wake_up_q(&wake_q);
|
|
return sem;
|
}
|
|
/*
|
* lock for reading
|
*/
|
static inline void __down_read(struct rw_semaphore *sem)
|
{
|
if (!rwsem_read_trylock(sem)) {
|
rwsem_down_read_slowpath(sem, TASK_UNINTERRUPTIBLE);
|
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
|
} else {
|
rwsem_set_reader_owned(sem);
|
}
|
}
|
|
static inline int __down_read_interruptible(struct rw_semaphore *sem)
|
{
|
if (!rwsem_read_trylock(sem)) {
|
if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_INTERRUPTIBLE)))
|
return -EINTR;
|
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
|
} else {
|
rwsem_set_reader_owned(sem);
|
}
|
return 0;
|
}
|
|
static inline int __down_read_killable(struct rw_semaphore *sem)
|
{
|
if (!rwsem_read_trylock(sem)) {
|
if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_KILLABLE)))
|
return -EINTR;
|
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
|
} else {
|
rwsem_set_reader_owned(sem);
|
}
|
return 0;
|
}
|
|
static inline int __down_read_trylock(struct rw_semaphore *sem)
|
{
|
long tmp;
|
|
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
|
|
/*
|
* Optimize for the case when the rwsem is not locked at all.
|
*/
|
tmp = RWSEM_UNLOCKED_VALUE;
|
do {
|
if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
|
tmp + RWSEM_READER_BIAS)) {
|
rwsem_set_reader_owned(sem);
|
trace_android_vh_record_rwsem_lock_starttime(current, jiffies);
|
return 1;
|
}
|
} while (!(tmp & RWSEM_READ_FAILED_MASK));
|
return 0;
|
}
|
|
/*
|
* lock for writing
|
*/
|
static inline void __down_write(struct rw_semaphore *sem)
|
{
|
long tmp = RWSEM_UNLOCKED_VALUE;
|
|
if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
|
RWSEM_WRITER_LOCKED))) {
|
rwsem_down_write_slowpath(sem, TASK_UNINTERRUPTIBLE);
|
} else {
|
trace_android_vh_record_rwsem_lock_starttime(current, jiffies);
|
rwsem_set_owner(sem);
|
}
|
}
|
|
static inline int __down_write_killable(struct rw_semaphore *sem)
|
{
|
long tmp = RWSEM_UNLOCKED_VALUE;
|
|
if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
|
RWSEM_WRITER_LOCKED))) {
|
if (IS_ERR(rwsem_down_write_slowpath(sem, TASK_KILLABLE)))
|
return -EINTR;
|
} else {
|
trace_android_vh_record_rwsem_lock_starttime(current, jiffies);
|
rwsem_set_owner(sem);
|
}
|
return 0;
|
}
|
|
static inline int __down_write_trylock(struct rw_semaphore *sem)
|
{
|
long tmp;
|
|
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
|
|
tmp = RWSEM_UNLOCKED_VALUE;
|
if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
|
RWSEM_WRITER_LOCKED)) {
|
rwsem_set_owner(sem);
|
trace_android_vh_record_rwsem_lock_starttime(current, jiffies);
|
return true;
|
}
|
return false;
|
}
|
|
/*
|
* unlock after reading
|
*/
|
static inline void __up_read(struct rw_semaphore *sem)
|
{
|
long tmp;
|
|
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
|
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
|
|
trace_android_vh_record_rwsem_lock_starttime(current, 0);
|
rwsem_clear_reader_owned(sem);
|
tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count);
|
DEBUG_RWSEMS_WARN_ON(tmp < 0, sem);
|
if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) ==
|
RWSEM_FLAG_WAITERS)) {
|
clear_wr_nonspinnable(sem);
|
rwsem_wake(sem, tmp);
|
}
|
trace_android_vh_rwsem_up_read_end(sem);
|
}
|
|
/*
|
* unlock after writing
|
*/
|
static inline void __up_write(struct rw_semaphore *sem)
|
{
|
long tmp;
|
|
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
|
/*
|
* sem->owner may differ from current if the ownership is transferred
|
* to an anonymous writer by setting the RWSEM_NONSPINNABLE bits.
|
*/
|
DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) &&
|
!rwsem_test_oflags(sem, RWSEM_NONSPINNABLE), sem);
|
|
trace_android_vh_record_rwsem_lock_starttime(current, 0);
|
rwsem_clear_owner(sem);
|
tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count);
|
if (unlikely(tmp & RWSEM_FLAG_WAITERS))
|
rwsem_wake(sem, tmp);
|
trace_android_vh_rwsem_up_write_end(sem);
|
}
|
|
/*
|
* downgrade write lock to read lock
|
*/
|
static inline void __downgrade_write(struct rw_semaphore *sem)
|
{
|
long tmp;
|
|
/*
|
* When downgrading from exclusive to shared ownership,
|
* anything inside the write-locked region cannot leak
|
* into the read side. In contrast, anything in the
|
* read-locked region is ok to be re-ordered into the
|
* write side. As such, rely on RELEASE semantics.
|
*/
|
DEBUG_RWSEMS_WARN_ON(rwsem_owner(sem) != current, sem);
|
tmp = atomic_long_fetch_add_release(
|
-RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count);
|
rwsem_set_reader_owned(sem);
|
if (tmp & RWSEM_FLAG_WAITERS)
|
rwsem_downgrade_wake(sem);
|
}
|
#endif
|
|
/*
|
* lock for reading
|
*/
|
void __sched down_read(struct rw_semaphore *sem)
|
{
|
might_sleep();
|
rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
|
|
LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
|
}
|
EXPORT_SYMBOL(down_read);
|
|
int __sched down_read_interruptible(struct rw_semaphore *sem)
|
{
|
might_sleep();
|
rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
|
|
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) {
|
rwsem_release(&sem->dep_map, _RET_IP_);
|
return -EINTR;
|
}
|
|
return 0;
|
}
|
EXPORT_SYMBOL(down_read_interruptible);
|
|
int __sched down_read_killable(struct rw_semaphore *sem)
|
{
|
might_sleep();
|
rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
|
|
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
|
rwsem_release(&sem->dep_map, _RET_IP_);
|
return -EINTR;
|
}
|
|
return 0;
|
}
|
EXPORT_SYMBOL(down_read_killable);
|
|
/*
|
* trylock for reading -- returns 1 if successful, 0 if contention
|
*/
|
int down_read_trylock(struct rw_semaphore *sem)
|
{
|
int ret = __down_read_trylock(sem);
|
|
if (ret == 1)
|
rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
|
return ret;
|
}
|
EXPORT_SYMBOL(down_read_trylock);
|
|
/*
|
* lock for writing
|
*/
|
void __sched down_write(struct rw_semaphore *sem)
|
{
|
might_sleep();
|
rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
|
LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
|
}
|
EXPORT_SYMBOL(down_write);
|
|
/*
|
* lock for writing
|
*/
|
int __sched down_write_killable(struct rw_semaphore *sem)
|
{
|
might_sleep();
|
rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
|
|
if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
|
__down_write_killable)) {
|
rwsem_release(&sem->dep_map, _RET_IP_);
|
return -EINTR;
|
}
|
|
return 0;
|
}
|
EXPORT_SYMBOL(down_write_killable);
|
|
/*
|
* trylock for writing -- returns 1 if successful, 0 if contention
|
*/
|
int down_write_trylock(struct rw_semaphore *sem)
|
{
|
int ret = __down_write_trylock(sem);
|
|
if (ret == 1)
|
rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
|
|
return ret;
|
}
|
EXPORT_SYMBOL(down_write_trylock);
|
|
/*
|
* release a read lock
|
*/
|
void up_read(struct rw_semaphore *sem)
|
{
|
rwsem_release(&sem->dep_map, _RET_IP_);
|
__up_read(sem);
|
}
|
EXPORT_SYMBOL(up_read);
|
|
/*
|
* release a write lock
|
*/
|
void up_write(struct rw_semaphore *sem)
|
{
|
rwsem_release(&sem->dep_map, _RET_IP_);
|
__up_write(sem);
|
}
|
EXPORT_SYMBOL(up_write);
|
|
/*
|
* downgrade write lock to read lock
|
*/
|
void downgrade_write(struct rw_semaphore *sem)
|
{
|
lock_downgrade(&sem->dep_map, _RET_IP_);
|
__downgrade_write(sem);
|
}
|
EXPORT_SYMBOL(downgrade_write);
|
|
#ifdef CONFIG_DEBUG_LOCK_ALLOC
|
|
void down_read_nested(struct rw_semaphore *sem, int subclass)
|
{
|
might_sleep();
|
rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
|
LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
|
}
|
EXPORT_SYMBOL(down_read_nested);
|
|
int down_read_killable_nested(struct rw_semaphore *sem, int subclass)
|
{
|
might_sleep();
|
rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
|
|
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
|
rwsem_release(&sem->dep_map, _RET_IP_);
|
return -EINTR;
|
}
|
|
return 0;
|
}
|
EXPORT_SYMBOL(down_read_killable_nested);
|
|
void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
|
{
|
might_sleep();
|
rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
|
LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
|
}
|
EXPORT_SYMBOL(_down_write_nest_lock);
|
|
void down_read_non_owner(struct rw_semaphore *sem)
|
{
|
might_sleep();
|
__down_read(sem);
|
#ifndef CONFIG_PREEMPT_RT
|
__rwsem_set_reader_owned(sem, NULL);
|
#endif
|
}
|
EXPORT_SYMBOL(down_read_non_owner);
|
|
void down_write_nested(struct rw_semaphore *sem, int subclass)
|
{
|
might_sleep();
|
rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
|
LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
|
}
|
EXPORT_SYMBOL(down_write_nested);
|
|
int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
|
{
|
might_sleep();
|
rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
|
|
if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
|
__down_write_killable)) {
|
rwsem_release(&sem->dep_map, _RET_IP_);
|
return -EINTR;
|
}
|
|
return 0;
|
}
|
EXPORT_SYMBOL(down_write_killable_nested);
|
|
void up_read_non_owner(struct rw_semaphore *sem)
|
{
|
#ifndef CONFIG_PREEMPT_RT
|
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
|
#endif
|
__up_read(sem);
|
}
|
EXPORT_SYMBOL(up_read_non_owner);
|
|
#endif
|
