From 102a0743326a03cd1a1202ceda21e175b7d3575c Mon Sep 17 00:00:00 2001
From: hc <hc@nodka.com>
Date: Tue, 20 Feb 2024 01:20:52 +0000
Subject: [PATCH] add new system file
---
kernel/kernel/locking/rwsem.c | 1621 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 1,569 insertions(+), 52 deletions(-)
diff --git a/kernel/kernel/locking/rwsem.c b/kernel/kernel/locking/rwsem.c
index 776308d..acd1fc7 100644
--- a/kernel/kernel/locking/rwsem.c
+++ b/kernel/kernel/locking/rwsem.c
@@ -3,17 +3,1542 @@
*
* Written by David Howells (dhowells@redhat.com).
* Derived from asm-i386/semaphore.h
+ *
+ * Writer lock-stealing by Alex Shi <alex.shi@intel.com>
+ * and Michel Lespinasse <walken@google.com>
+ *
+ * Optimistic spinning by Tim Chen <tim.c.chen@intel.com>
+ * and Davidlohr Bueso <davidlohr@hp.com>. Based on mutexes.
+ *
+ * Rwsem count bit fields re-definition and rwsem rearchitecture by
+ * Waiman Long <longman@redhat.com> and
+ * Peter Zijlstra <peterz@infradead.org>.
*/
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/sched.h>
+#include <linux/sched/rt.h>
+#include <linux/sched/task.h>
#include <linux/sched/debug.h>
+#include <linux/sched/wake_q.h>
+#include <linux/sched/signal.h>
+#include <linux/sched/clock.h>
#include <linux/export.h>
#include <linux/rwsem.h>
#include <linux/atomic.h>
-#include "rwsem.h"
+#include "lock_events.h"
+#include <trace/hooks/rwsem.h>
+#include <trace/hooks/dtask.h>
+
+/*
+ * The least significant 3 bits of the owner value has the following
+ * meanings when set.
+ * - Bit 0: RWSEM_READER_OWNED - The rwsem is owned by readers
+ * - Bit 1: RWSEM_RD_NONSPINNABLE - Readers cannot spin on this lock.
+ * - Bit 2: RWSEM_WR_NONSPINNABLE - Writers cannot spin on this lock.
+ *
+ * When the rwsem is either owned by an anonymous writer, or it is
+ * reader-owned, but a spinning writer has timed out, both nonspinnable
+ * bits will be set to disable optimistic spinning by readers and writers.
+ * In the later case, the last unlocking reader should then check the
+ * writer nonspinnable bit and clear it only to give writers preference
+ * to acquire the lock via optimistic spinning, but not readers. Similar
+ * action is also done in the reader slowpath.
+
+ * When a writer acquires a rwsem, it puts its task_struct pointer
+ * into the owner field. It is cleared after an unlock.
+ *
+ * When a reader acquires a rwsem, it will also puts its task_struct
+ * pointer into the owner field with the RWSEM_READER_OWNED bit set.
+ * On unlock, the owner field will largely be left untouched. So
+ * for a free or reader-owned rwsem, the owner value may contain
+ * information about the last reader that acquires the rwsem.
+ *
+ * That information may be helpful in debugging cases where the system
+ * seems to hang on a reader owned rwsem especially if only one reader
+ * is involved. Ideally we would like to track all the readers that own
+ * a rwsem, but the overhead is simply too big.
+ *
+ * Reader optimistic spinning is helpful when the reader critical section
+ * is short and there aren't that many readers around. It makes readers
+ * relatively more preferred than writers. When a writer times out spinning
+ * on a reader-owned lock and set the nospinnable bits, there are two main
+ * reasons for that.
+ *
+ * 1) The reader critical section is long, perhaps the task sleeps after
+ * acquiring the read lock.
+ * 2) There are just too many readers contending the lock causing it to
+ * take a while to service all of them.
+ *
+ * In the former case, long reader critical section will impede the progress
+ * of writers which is usually more important for system performance. In
+ * the later case, reader optimistic spinning tends to make the reader
+ * groups that contain readers that acquire the lock together smaller
+ * leading to more of them. That may hurt performance in some cases. In
+ * other words, the setting of nonspinnable bits indicates that reader
+ * optimistic spinning may not be helpful for those workloads that cause
+ * it.
+ *
+ * Therefore, any writers that had observed the setting of the writer
+ * nonspinnable bit for a given rwsem after they fail to acquire the lock
+ * via optimistic spinning will set the reader nonspinnable bit once they
+ * acquire the write lock. Similarly, readers that observe the setting
+ * of reader nonspinnable bit at slowpath entry will set the reader
+ * nonspinnable bits when they acquire the read lock via the wakeup path.
+ *
+ * Once the reader nonspinnable bit is on, it will only be reset when
+ * a writer is able to acquire the rwsem in the fast path or somehow a
+ * reader or writer in the slowpath doesn't observe the nonspinable bit.
+ *
+ * This is to discourage reader optmistic spinning on that particular
+ * rwsem and make writers more preferred. This adaptive disabling of reader
+ * optimistic spinning will alleviate the negative side effect of this
+ * feature.
+ */
+#define RWSEM_READER_OWNED (1UL << 0)
+#define RWSEM_RD_NONSPINNABLE (1UL << 1)
+#define RWSEM_WR_NONSPINNABLE (1UL << 2)
+#define RWSEM_NONSPINNABLE (RWSEM_RD_NONSPINNABLE | RWSEM_WR_NONSPINNABLE)
+#define RWSEM_OWNER_FLAGS_MASK (RWSEM_READER_OWNED | RWSEM_NONSPINNABLE)
+
+#ifdef CONFIG_DEBUG_RWSEMS
+# define DEBUG_RWSEMS_WARN_ON(c, sem) do { \
+ if (!debug_locks_silent && \
+ WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, magic = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
+ #c, atomic_long_read(&(sem)->count), \
+ (unsigned long) sem->magic, \
+ atomic_long_read(&(sem)->owner), (long)current, \
+ list_empty(&(sem)->wait_list) ? "" : "not ")) \
+ debug_locks_off(); \
+ } while (0)
+#else
+# define DEBUG_RWSEMS_WARN_ON(c, sem)
+#endif
+
+/*
+ * On 64-bit architectures, the bit definitions of the count are:
+ *
+ * Bit 0 - writer locked bit
+ * Bit 1 - waiters present bit
+ * Bit 2 - lock handoff bit
+ * Bits 3-7 - reserved
+ * Bits 8-62 - 55-bit reader count
+ * Bit 63 - read fail bit
+ *
+ * On 32-bit architectures, the bit definitions of the count are:
+ *
+ * Bit 0 - writer locked bit
+ * Bit 1 - waiters present bit
+ * Bit 2 - lock handoff bit
+ * Bits 3-7 - reserved
+ * Bits 8-30 - 23-bit reader count
+ * Bit 31 - read fail bit
+ *
+ * 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.
+ *
+ * atomic_long_fetch_add() is used to obtain reader lock, whereas
+ * atomic_long_cmpxchg() will be used to obtain writer lock.
+ *
+ * There are three places where the lock handoff bit may be set or cleared.
+ * 1) rwsem_mark_wake() for readers.
+ * 2) rwsem_try_write_lock() for writers.
+ * 3) Error path of rwsem_down_write_slowpath().
+ *
+ * For all the above cases, wait_lock will be held. A writer must also
+ * 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.
+ */
+#define RWSEM_WRITER_LOCKED (1UL << 0)
+#define RWSEM_FLAG_WAITERS (1UL << 1)
+#define RWSEM_FLAG_HANDOFF (1UL << 2)
+#define RWSEM_FLAG_READFAIL (1UL << (BITS_PER_LONG - 1))
+
+#define RWSEM_READER_SHIFT 8
+#define RWSEM_READER_BIAS (1UL << RWSEM_READER_SHIFT)
+#define RWSEM_READER_MASK (~(RWSEM_READER_BIAS - 1))
+#define RWSEM_WRITER_MASK RWSEM_WRITER_LOCKED
+#define RWSEM_LOCK_MASK (RWSEM_WRITER_MASK|RWSEM_READER_MASK)
+#define RWSEM_READ_FAILED_MASK (RWSEM_WRITER_MASK|RWSEM_FLAG_WAITERS|\
+ RWSEM_FLAG_HANDOFF|RWSEM_FLAG_READFAIL)
+
+/*
+ * All writes to owner are protected by WRITE_ONCE() to make sure that
+ * store tearing can't happen as optimistic spinners may read and use
+ * the owner value concurrently without lock. Read from owner, however,
+ * may not need READ_ONCE() as long as the pointer value is only used
+ * for comparison and isn't being dereferenced.
+ */
+static inline void rwsem_set_owner(struct rw_semaphore *sem)
+{
+ atomic_long_set(&sem->owner, (long)current);
+ trace_android_vh_rwsem_set_owner(sem);
+}
+
+static inline void rwsem_clear_owner(struct rw_semaphore *sem)
+{
+ atomic_long_set(&sem->owner, 0);
+}
+
+/*
+ * Test the flags in the owner field.
+ */
+static inline bool rwsem_test_oflags(struct rw_semaphore *sem, long flags)
+{
+ return atomic_long_read(&sem->owner) & flags;
+}
+
+/*
+ * The task_struct pointer of the last owning reader will be left in
+ * the owner field.
+ *
+ * Note that the owner value just indicates the task has owned the rwsem
+ * previously, it may not be the real owner or one of the real owners
+ * anymore when that field is examined, so take it with a grain of salt.
+ *
+ * The reader non-spinnable bit is preserved.
+ */
+static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
+ struct task_struct *owner)
+{
+ unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED |
+ (atomic_long_read(&sem->owner) & RWSEM_RD_NONSPINNABLE);
+
+ atomic_long_set(&sem->owner, val);
+}
+
+static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
+{
+ __rwsem_set_reader_owned(sem, current);
+ trace_android_vh_rwsem_set_reader_owned(sem);
+}
+
+/*
+ * Return true if the rwsem is owned by a reader.
+ */
+static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
+{
+#ifdef CONFIG_DEBUG_RWSEMS
+ /*
+ * Check the count to see if it is write-locked.
+ */
+ long count = atomic_long_read(&sem->count);
+
+ if (count & RWSEM_WRITER_MASK)
+ return false;
+#endif
+ return rwsem_test_oflags(sem, RWSEM_READER_OWNED);
+}
+
+#ifdef CONFIG_DEBUG_RWSEMS
+/*
+ * With CONFIG_DEBUG_RWSEMS configured, it will make sure that if there
+ * is a task pointer in owner of a reader-owned rwsem, it will be the
+ * real owner or one of the real owners. The only exception is when the
+ * unlock is done by up_read_non_owner().
+ */
+static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
+{
+ unsigned long val = atomic_long_read(&sem->owner);
+
+ while ((val & ~RWSEM_OWNER_FLAGS_MASK) == (unsigned long)current) {
+ if (atomic_long_try_cmpxchg(&sem->owner, &val,
+ val & RWSEM_OWNER_FLAGS_MASK))
+ return;
+ }
+}
+#else
+static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
+{
+}
+#endif
+
+/*
+ * Set the RWSEM_NONSPINNABLE bits if the RWSEM_READER_OWNED flag
+ * remains set. Otherwise, the operation will be aborted.
+ */
+static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
+{
+ unsigned long owner = atomic_long_read(&sem->owner);
+
+ do {
+ if (!(owner & RWSEM_READER_OWNED))
+ break;
+ if (owner & RWSEM_NONSPINNABLE)
+ break;
+ } while (!atomic_long_try_cmpxchg(&sem->owner, &owner,
+ owner | RWSEM_NONSPINNABLE));
+}
+
+static inline bool rwsem_read_trylock(struct rw_semaphore *sem)
+{
+ long cnt = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
+ if (WARN_ON_ONCE(cnt < 0))
+ rwsem_set_nonspinnable(sem);
+
+ if ((cnt & RWSEM_READ_FAILED_MASK) == 0)
+ trace_android_vh_record_rwsem_lock_starttime(current, jiffies);
+
+ return !(cnt & RWSEM_READ_FAILED_MASK);
+}
+
+/*
+ * Return just the real task structure pointer of the owner
+ */
+static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
+{
+ return (struct task_struct *)
+ (atomic_long_read(&sem->owner) & ~RWSEM_OWNER_FLAGS_MASK);
+}
+
+/*
+ * Return the real task structure pointer of the owner and the embedded
+ * flags in the owner. pflags must be non-NULL.
+ */
+static inline struct task_struct *
+rwsem_owner_flags(struct rw_semaphore *sem, unsigned long *pflags)
+{
+ unsigned long owner = atomic_long_read(&sem->owner);
+
+ *pflags = owner & RWSEM_OWNER_FLAGS_MASK;
+ return (struct task_struct *)(owner & ~RWSEM_OWNER_FLAGS_MASK);
+}
+
+/*
+ * Guide to the rw_semaphore's count field.
+ *
+ * When the RWSEM_WRITER_LOCKED bit in count is set, the lock is owned
+ * by a writer.
+ *
+ * The lock is owned by readers when
+ * (1) the RWSEM_WRITER_LOCKED isn't set in count,
+ * (2) some of the reader bits are set in count, and
+ * (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
+ * and a writer has just released the lock. So another writer may steal
+ * the lock immediately after that.
+ */
+
+/*
+ * Initialize an rwsem:
+ */
+void __init_rwsem(struct rw_semaphore *sem, const char *name,
+ struct lock_class_key *key)
+{
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+ /*
+ * 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
+#ifdef CONFIG_DEBUG_RWSEMS
+ sem->magic = sem;
+#endif
+ atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
+ 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);
+
+#define rwsem_first_waiter(sem) \
+ list_first_entry(&sem->wait_list, struct rwsem_waiter, list)
+
+enum rwsem_wake_type {
+ RWSEM_WAKE_ANY, /* Wake whatever's at head of wait list */
+ RWSEM_WAKE_READERS, /* Wake readers only */
+ RWSEM_WAKE_READ_OWNED /* Waker thread holds the read lock */
+};
+
+enum writer_wait_state {
+ WRITER_NOT_FIRST, /* Writer is not first in wait list */
+ 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();
+ trace_android_vh_rwsem_can_spin_on_owner(sem, &ret, nonspinnable == RWSEM_WR_NONSPINNABLE);
+
+ 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;
+ int cnt = 0;
+ bool time_out = false;
+
+ owner = rwsem_owner_flags(sem, &flags);
+ state = rwsem_owner_state(owner, flags, nonspinnable);
+ if (state != OWNER_WRITER)
+ return state;
+
+ rcu_read_lock();
+ for (;;) {
+ trace_android_vh_rwsem_opt_spin_start(sem, &time_out, &cnt, true);
+ if (time_out)
+ break;
+ /*
+ * 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;
+ int cnt = 0;
+ bool time_out = false;
+ 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;
+
+ trace_android_vh_rwsem_opt_spin_start(sem, &time_out, &cnt, false);
+ if (time_out)
+ break;
+
+ 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);
+ trace_android_vh_rwsem_opt_spin_finish(sem, taken, wlock);
+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);
+ trace_android_vh_record_rwsem_lock_starttime(
+ current, jiffies);
+ 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);
+}
/*
* lock for reading
@@ -24,10 +1549,22 @@
rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
- rwsem_set_reader_owned(sem);
}
-
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)
{
@@ -35,14 +1572,12 @@
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, 1, _RET_IP_);
+ rwsem_release(&sem->dep_map, _RET_IP_);
return -EINTR;
}
- rwsem_set_reader_owned(sem);
return 0;
}
-
EXPORT_SYMBOL(down_read_killable);
/*
@@ -52,13 +1587,10 @@
{
int ret = __down_read_trylock(sem);
- if (ret == 1) {
+ if (ret == 1)
rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
- rwsem_set_reader_owned(sem);
- }
return ret;
}
-
EXPORT_SYMBOL(down_read_trylock);
/*
@@ -68,11 +1600,8 @@
{
might_sleep();
rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
-
LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
- rwsem_set_owner(sem);
}
-
EXPORT_SYMBOL(down_write);
/*
@@ -83,15 +1612,14 @@
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, 1, _RET_IP_);
+ if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
+ __down_write_killable)) {
+ rwsem_release(&sem->dep_map, _RET_IP_);
return -EINTR;
}
- rwsem_set_owner(sem);
return 0;
}
-
EXPORT_SYMBOL(down_write_killable);
/*
@@ -101,14 +1629,11 @@
{
int ret = __down_write_trylock(sem);
- if (ret == 1) {
+ if (ret == 1)
rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
- rwsem_set_owner(sem);
- }
return ret;
}
-
EXPORT_SYMBOL(down_write_trylock);
/*
@@ -116,12 +1641,9 @@
*/
void up_read(struct rw_semaphore *sem)
{
- rwsem_release(&sem->dep_map, 1, _RET_IP_);
- DEBUG_RWSEMS_WARN_ON(sem->owner != RWSEM_READER_OWNED);
-
+ rwsem_release(&sem->dep_map, _RET_IP_);
__up_read(sem);
}
-
EXPORT_SYMBOL(up_read);
/*
@@ -129,13 +1651,10 @@
*/
void up_write(struct rw_semaphore *sem)
{
- rwsem_release(&sem->dep_map, 1, _RET_IP_);
- DEBUG_RWSEMS_WARN_ON(sem->owner != current);
-
- rwsem_clear_owner(sem);
+ rwsem_release(&sem->dep_map, _RET_IP_);
+ trace_android_vh_rwsem_write_finished(sem);
__up_write(sem);
}
-
EXPORT_SYMBOL(up_write);
/*
@@ -144,12 +1663,9 @@
void downgrade_write(struct rw_semaphore *sem)
{
lock_downgrade(&sem->dep_map, _RET_IP_);
- DEBUG_RWSEMS_WARN_ON(sem->owner != current);
-
- rwsem_set_reader_owned(sem);
+ trace_android_vh_rwsem_write_finished(sem);
__downgrade_write(sem);
}
-
EXPORT_SYMBOL(downgrade_write);
#ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -158,43 +1674,46 @@
{
might_sleep();
rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
-
LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
- rwsem_set_reader_owned(sem);
}
-
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);
- rwsem_set_owner(sem);
}
-
EXPORT_SYMBOL(_down_write_nest_lock);
void down_read_non_owner(struct rw_semaphore *sem)
{
might_sleep();
-
__down_read(sem);
- rwsem_set_reader_owned(sem);
+ __rwsem_set_reader_owned(sem, NULL);
}
-
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);
- rwsem_set_owner(sem);
}
-
EXPORT_SYMBOL(down_write_nested);
int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
@@ -202,23 +1721,21 @@
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, 1, _RET_IP_);
+ if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
+ __down_write_killable)) {
+ rwsem_release(&sem->dep_map, _RET_IP_);
return -EINTR;
}
- rwsem_set_owner(sem);
return 0;
}
-
EXPORT_SYMBOL(down_write_killable_nested);
void up_read_non_owner(struct rw_semaphore *sem)
{
- DEBUG_RWSEMS_WARN_ON(sem->owner != RWSEM_READER_OWNED);
+ DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
__up_read(sem);
}
-
EXPORT_SYMBOL(up_read_non_owner);
#endif
--
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