// SPDX-License-Identifier: GPL-2.0-only
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/*
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* kernel/locking/mutex.c
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*
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* Mutexes: blocking mutual exclusion locks
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*
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* Started by Ingo Molnar:
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*
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* Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
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*
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* Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
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* David Howells for suggestions and improvements.
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*
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* - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline
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* from the -rt tree, where it was originally implemented for rtmutexes
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* by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale
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* and Sven Dietrich.
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*
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* Also see Documentation/locking/mutex-design.rst.
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*/
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#include <linux/mutex.h>
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#include <linux/ww_mutex.h>
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#include <linux/sched/signal.h>
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#include <linux/sched/rt.h>
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#include <linux/sched/wake_q.h>
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#include <linux/sched/debug.h>
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#include <linux/export.h>
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#include <linux/spinlock.h>
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#include <linux/interrupt.h>
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#include <linux/debug_locks.h>
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#include <linux/osq_lock.h>
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#ifdef CONFIG_DEBUG_MUTEXES
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# include "mutex-debug.h"
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#else
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# include "mutex.h"
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#endif
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#include <trace/hooks/dtask.h>
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void
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__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
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{
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atomic_long_set(&lock->owner, 0);
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spin_lock_init(&lock->wait_lock);
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INIT_LIST_HEAD(&lock->wait_list);
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#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
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osq_lock_init(&lock->osq);
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#endif
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debug_mutex_init(lock, name, key);
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}
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EXPORT_SYMBOL(__mutex_init);
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/*
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* @owner: contains: 'struct task_struct *' to the current lock owner,
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* NULL means not owned. Since task_struct pointers are aligned at
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* at least L1_CACHE_BYTES, we have low bits to store extra state.
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*
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* Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
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* Bit1 indicates unlock needs to hand the lock to the top-waiter
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* Bit2 indicates handoff has been done and we're waiting for pickup.
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*/
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#define MUTEX_FLAG_WAITERS 0x01
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#define MUTEX_FLAG_HANDOFF 0x02
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#define MUTEX_FLAG_PICKUP 0x04
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#define MUTEX_FLAGS 0x07
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/*
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* Internal helper function; C doesn't allow us to hide it :/
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*
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* DO NOT USE (outside of mutex code).
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*/
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static inline struct task_struct *__mutex_owner(struct mutex *lock)
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{
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return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
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}
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static inline struct task_struct *__owner_task(unsigned long owner)
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{
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return (struct task_struct *)(owner & ~MUTEX_FLAGS);
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}
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bool mutex_is_locked(struct mutex *lock)
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{
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return __mutex_owner(lock) != NULL;
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}
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EXPORT_SYMBOL(mutex_is_locked);
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__must_check enum mutex_trylock_recursive_enum
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mutex_trylock_recursive(struct mutex *lock)
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{
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if (unlikely(__mutex_owner(lock) == current))
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return MUTEX_TRYLOCK_RECURSIVE;
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return mutex_trylock(lock);
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}
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EXPORT_SYMBOL(mutex_trylock_recursive);
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static inline unsigned long __owner_flags(unsigned long owner)
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{
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return owner & MUTEX_FLAGS;
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}
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/*
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* Trylock variant that retuns the owning task on failure.
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*/
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static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
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{
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unsigned long owner, curr = (unsigned long)current;
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owner = atomic_long_read(&lock->owner);
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for (;;) { /* must loop, can race against a flag */
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unsigned long old, flags = __owner_flags(owner);
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unsigned long task = owner & ~MUTEX_FLAGS;
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if (task) {
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if (likely(task != curr))
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break;
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if (likely(!(flags & MUTEX_FLAG_PICKUP)))
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break;
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flags &= ~MUTEX_FLAG_PICKUP;
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} else {
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#ifdef CONFIG_DEBUG_MUTEXES
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DEBUG_LOCKS_WARN_ON(flags & MUTEX_FLAG_PICKUP);
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#endif
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}
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/*
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* We set the HANDOFF bit, we must make sure it doesn't live
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* past the point where we acquire it. This would be possible
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* if we (accidentally) set the bit on an unlocked mutex.
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*/
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flags &= ~MUTEX_FLAG_HANDOFF;
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old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags);
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if (old == owner)
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return NULL;
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owner = old;
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}
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return __owner_task(owner);
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}
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/*
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* Actual trylock that will work on any unlocked state.
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*/
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static inline bool __mutex_trylock(struct mutex *lock)
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{
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return !__mutex_trylock_or_owner(lock);
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}
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#ifndef CONFIG_DEBUG_LOCK_ALLOC
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/*
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* Lockdep annotations are contained to the slow paths for simplicity.
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* There is nothing that would stop spreading the lockdep annotations outwards
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* except more code.
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*/
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/*
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* Optimistic trylock that only works in the uncontended case. Make sure to
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* follow with a __mutex_trylock() before failing.
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*/
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static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
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{
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unsigned long curr = (unsigned long)current;
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unsigned long zero = 0UL;
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if (atomic_long_try_cmpxchg_acquire(&lock->owner, &zero, curr)) {
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trace_android_vh_record_mutex_lock_starttime(current, jiffies);
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return true;
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}
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return false;
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}
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static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
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{
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unsigned long curr = (unsigned long)current;
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if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr)
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return true;
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return false;
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}
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#endif
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static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
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{
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atomic_long_or(flag, &lock->owner);
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}
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static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag)
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{
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atomic_long_andnot(flag, &lock->owner);
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}
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static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter)
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{
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return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
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}
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/*
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* Add @waiter to a given location in the lock wait_list and set the
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* FLAG_WAITERS flag if it's the first waiter.
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*/
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static void
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__mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
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struct list_head *list)
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{
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bool already_on_list = false;
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debug_mutex_add_waiter(lock, waiter, current);
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trace_android_vh_alter_mutex_list_add(lock, waiter, list, &already_on_list);
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if (!already_on_list)
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list_add_tail(&waiter->list, list);
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if (__mutex_waiter_is_first(lock, waiter))
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__mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
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}
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static void
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__mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter)
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{
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list_del(&waiter->list);
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if (likely(list_empty(&lock->wait_list)))
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__mutex_clear_flag(lock, MUTEX_FLAGS);
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debug_mutex_remove_waiter(lock, waiter, current);
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}
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/*
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* Give up ownership to a specific task, when @task = NULL, this is equivalent
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* to a regular unlock. Sets PICKUP on a handoff, clears HANDOF, preserves
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* WAITERS. Provides RELEASE semantics like a regular unlock, the
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* __mutex_trylock() provides a matching ACQUIRE semantics for the handoff.
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*/
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static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
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{
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unsigned long owner = atomic_long_read(&lock->owner);
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for (;;) {
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unsigned long old, new;
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#ifdef CONFIG_DEBUG_MUTEXES
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DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
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DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
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#endif
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new = (owner & MUTEX_FLAG_WAITERS);
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new |= (unsigned long)task;
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if (task)
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new |= MUTEX_FLAG_PICKUP;
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old = atomic_long_cmpxchg_release(&lock->owner, owner, new);
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if (old == owner)
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break;
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owner = old;
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}
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}
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#ifndef CONFIG_DEBUG_LOCK_ALLOC
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/*
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* We split the mutex lock/unlock logic into separate fastpath and
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* slowpath functions, to reduce the register pressure on the fastpath.
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* We also put the fastpath first in the kernel image, to make sure the
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* branch is predicted by the CPU as default-untaken.
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*/
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static void __sched __mutex_lock_slowpath(struct mutex *lock);
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/**
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* mutex_lock - acquire the mutex
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* @lock: the mutex to be acquired
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*
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* Lock the mutex exclusively for this task. If the mutex is not
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* available right now, it will sleep until it can get it.
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*
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* The mutex must later on be released by the same task that
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* acquired it. Recursive locking is not allowed. The task
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* may not exit without first unlocking the mutex. Also, kernel
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* memory where the mutex resides must not be freed with
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* the mutex still locked. The mutex must first be initialized
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* (or statically defined) before it can be locked. memset()-ing
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* the mutex to 0 is not allowed.
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*
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* (The CONFIG_DEBUG_MUTEXES .config option turns on debugging
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* checks that will enforce the restrictions and will also do
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* deadlock debugging)
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*
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* This function is similar to (but not equivalent to) down().
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*/
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void __sched mutex_lock(struct mutex *lock)
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{
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might_sleep();
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if (!__mutex_trylock_fast(lock))
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__mutex_lock_slowpath(lock);
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}
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EXPORT_SYMBOL(mutex_lock);
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#endif
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/*
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* Wait-Die:
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* The newer transactions are killed when:
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* It (the new transaction) makes a request for a lock being held
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* by an older transaction.
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*
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* Wound-Wait:
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* The newer transactions are wounded when:
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* An older transaction makes a request for a lock being held by
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* the newer transaction.
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*/
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/*
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* Associate the ww_mutex @ww with the context @ww_ctx under which we acquired
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* it.
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*/
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static __always_inline void
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ww_mutex_lock_acquired(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
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{
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#ifdef CONFIG_DEBUG_MUTEXES
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/*
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* If this WARN_ON triggers, you used ww_mutex_lock to acquire,
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* but released with a normal mutex_unlock in this call.
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*
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* This should never happen, always use ww_mutex_unlock.
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*/
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DEBUG_LOCKS_WARN_ON(ww->ctx);
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/*
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* Not quite done after calling ww_acquire_done() ?
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*/
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DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
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if (ww_ctx->contending_lock) {
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/*
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* After -EDEADLK you tried to
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* acquire a different ww_mutex? Bad!
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*/
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DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
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/*
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* You called ww_mutex_lock after receiving -EDEADLK,
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* but 'forgot' to unlock everything else first?
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*/
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DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
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ww_ctx->contending_lock = NULL;
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}
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/*
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* Naughty, using a different class will lead to undefined behavior!
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*/
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DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
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#endif
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ww_ctx->acquired++;
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ww->ctx = ww_ctx;
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}
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/*
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* Determine if context @a is 'after' context @b. IOW, @a is a younger
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* transaction than @b and depending on algorithm either needs to wait for
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* @b or die.
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*/
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static inline bool __sched
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__ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
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{
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return (signed long)(a->stamp - b->stamp) > 0;
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}
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/*
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* Wait-Die; wake a younger waiter context (when locks held) such that it can
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* die.
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*
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* Among waiters with context, only the first one can have other locks acquired
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* already (ctx->acquired > 0), because __ww_mutex_add_waiter() and
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* __ww_mutex_check_kill() wake any but the earliest context.
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*/
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static bool __sched
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__ww_mutex_die(struct mutex *lock, struct mutex_waiter *waiter,
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struct ww_acquire_ctx *ww_ctx)
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{
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if (!ww_ctx->is_wait_die)
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return false;
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if (waiter->ww_ctx->acquired > 0 &&
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__ww_ctx_stamp_after(waiter->ww_ctx, ww_ctx)) {
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debug_mutex_wake_waiter(lock, waiter);
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wake_up_process(waiter->task);
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}
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return true;
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}
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/*
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* Wound-Wait; wound a younger @hold_ctx if it holds the lock.
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*
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* Wound the lock holder if there are waiters with older transactions than
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* the lock holders. Even if multiple waiters may wound the lock holder,
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* it's sufficient that only one does.
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*/
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static bool __ww_mutex_wound(struct mutex *lock,
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struct ww_acquire_ctx *ww_ctx,
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struct ww_acquire_ctx *hold_ctx)
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{
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struct task_struct *owner = __mutex_owner(lock);
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lockdep_assert_held(&lock->wait_lock);
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/*
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* Possible through __ww_mutex_add_waiter() when we race with
|
* ww_mutex_set_context_fastpath(). In that case we'll get here again
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* through __ww_mutex_check_waiters().
|
*/
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if (!hold_ctx)
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return false;
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/*
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* Can have !owner because of __mutex_unlock_slowpath(), but if owner,
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* it cannot go away because we'll have FLAG_WAITERS set and hold
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* wait_lock.
|
*/
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if (!owner)
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return false;
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if (ww_ctx->acquired > 0 && __ww_ctx_stamp_after(hold_ctx, ww_ctx)) {
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hold_ctx->wounded = 1;
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/*
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* wake_up_process() paired with set_current_state()
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* inserts sufficient barriers to make sure @owner either sees
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* it's wounded in __ww_mutex_check_kill() or has a
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* wakeup pending to re-read the wounded state.
|
*/
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if (owner != current)
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wake_up_process(owner);
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return true;
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}
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|
return false;
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}
|
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/*
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* We just acquired @lock under @ww_ctx, if there are later contexts waiting
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* behind us on the wait-list, check if they need to die, or wound us.
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*
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* See __ww_mutex_add_waiter() for the list-order construction; basically the
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* list is ordered by stamp, smallest (oldest) first.
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*
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* This relies on never mixing wait-die/wound-wait on the same wait-list;
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* which is currently ensured by that being a ww_class property.
|
*
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* The current task must not be on the wait list.
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*/
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static void __sched
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__ww_mutex_check_waiters(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
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{
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struct mutex_waiter *cur;
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lockdep_assert_held(&lock->wait_lock);
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list_for_each_entry(cur, &lock->wait_list, list) {
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if (!cur->ww_ctx)
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continue;
|
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if (__ww_mutex_die(lock, cur, ww_ctx) ||
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__ww_mutex_wound(lock, cur->ww_ctx, ww_ctx))
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break;
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}
|
}
|
|
/*
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* After acquiring lock with fastpath, where we do not hold wait_lock, set ctx
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* and wake up any waiters so they can recheck.
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*/
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static __always_inline void
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ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
|
{
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ww_mutex_lock_acquired(lock, ctx);
|
|
/*
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* The lock->ctx update should be visible on all cores before
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* the WAITERS check is done, otherwise contended waiters might be
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* missed. The contended waiters will either see ww_ctx == NULL
|
* and keep spinning, or it will acquire wait_lock, add itself
|
* to waiter list and sleep.
|
*/
|
smp_mb(); /* See comments above and below. */
|
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/*
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* [W] ww->ctx = ctx [W] MUTEX_FLAG_WAITERS
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* MB MB
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* [R] MUTEX_FLAG_WAITERS [R] ww->ctx
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*
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* The memory barrier above pairs with the memory barrier in
|
* __ww_mutex_add_waiter() and makes sure we either observe ww->ctx
|
* and/or !empty list.
|
*/
|
if (likely(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS)))
|
return;
|
|
/*
|
* Uh oh, we raced in fastpath, check if any of the waiters need to
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* die or wound us.
|
*/
|
spin_lock(&lock->base.wait_lock);
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__ww_mutex_check_waiters(&lock->base, ctx);
|
spin_unlock(&lock->base.wait_lock);
|
}
|
|
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
|
|
static inline
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bool ww_mutex_spin_on_owner(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
|
struct mutex_waiter *waiter)
|
{
|
struct ww_mutex *ww;
|
|
ww = container_of(lock, struct ww_mutex, base);
|
|
/*
|
* If ww->ctx is set the contents are undefined, only
|
* by acquiring wait_lock there is a guarantee that
|
* they are not invalid when reading.
|
*
|
* As such, when deadlock detection needs to be
|
* performed the optimistic spinning cannot be done.
|
*
|
* Check this in every inner iteration because we may
|
* be racing against another thread's ww_mutex_lock.
|
*/
|
if (ww_ctx->acquired > 0 && READ_ONCE(ww->ctx))
|
return false;
|
|
/*
|
* If we aren't on the wait list yet, cancel the spin
|
* if there are waiters. We want to avoid stealing the
|
* lock from a waiter with an earlier stamp, since the
|
* other thread may already own a lock that we also
|
* need.
|
*/
|
if (!waiter && (atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS))
|
return false;
|
|
/*
|
* Similarly, stop spinning if we are no longer the
|
* first waiter.
|
*/
|
if (waiter && !__mutex_waiter_is_first(lock, waiter))
|
return false;
|
|
return true;
|
}
|
|
/*
|
* Look out! "owner" is an entirely speculative pointer access and not
|
* reliable.
|
*
|
* "noinline" so that this function shows up on perf profiles.
|
*/
|
static noinline
|
bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner,
|
struct ww_acquire_ctx *ww_ctx, struct mutex_waiter *waiter)
|
{
|
bool ret = true;
|
|
rcu_read_lock();
|
while (__mutex_owner(lock) == owner) {
|
/*
|
* Ensure we emit the owner->on_cpu, dereference _after_
|
* checking lock->owner still matches owner. If that fails,
|
* owner might point to freed memory. If it still matches,
|
* the rcu_read_lock() ensures the memory stays valid.
|
*/
|
barrier();
|
|
/*
|
* Use vcpu_is_preempted to detect lock holder preemption issue.
|
*/
|
if (!owner->on_cpu || need_resched() ||
|
vcpu_is_preempted(task_cpu(owner))) {
|
ret = false;
|
break;
|
}
|
|
if (ww_ctx && !ww_mutex_spin_on_owner(lock, ww_ctx, waiter)) {
|
ret = false;
|
break;
|
}
|
|
cpu_relax();
|
}
|
rcu_read_unlock();
|
|
return ret;
|
}
|
|
/*
|
* Initial check for entering the mutex spinning loop
|
*/
|
static inline int mutex_can_spin_on_owner(struct mutex *lock)
|
{
|
struct task_struct *owner;
|
int retval = 1;
|
|
if (need_resched())
|
return 0;
|
|
rcu_read_lock();
|
owner = __mutex_owner(lock);
|
|
/*
|
* As lock holder preemption issue, we both skip spinning if task is not
|
* on cpu or its cpu is preempted
|
*/
|
if (owner)
|
retval = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
|
rcu_read_unlock();
|
|
/*
|
* If lock->owner is not set, the mutex has been released. Return true
|
* such that we'll trylock in the spin path, which is a faster option
|
* than the blocking slow path.
|
*/
|
return retval;
|
}
|
|
/*
|
* Optimistic spinning.
|
*
|
* We try to spin for acquisition when we find that the lock owner
|
* is currently running on a (different) CPU and while we don't
|
* need to reschedule. The rationale is that if the lock owner is
|
* running, it is likely to release the lock soon.
|
*
|
* The mutex spinners are queued up using MCS lock so that only one
|
* spinner can compete for the mutex. However, if mutex spinning isn't
|
* going to happen, there is no point in going through the lock/unlock
|
* overhead.
|
*
|
* Returns true when the lock was taken, otherwise false, indicating
|
* that we need to jump to the slowpath and sleep.
|
*
|
* The waiter flag is set to true if the spinner is a waiter in the wait
|
* queue. The waiter-spinner will spin on the lock directly and concurrently
|
* with the spinner at the head of the OSQ, if present, until the owner is
|
* changed to itself.
|
*/
|
static __always_inline bool
|
mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
|
struct mutex_waiter *waiter)
|
{
|
if (!waiter) {
|
/*
|
* The purpose of the mutex_can_spin_on_owner() function is
|
* to eliminate the overhead of osq_lock() and osq_unlock()
|
* in case spinning isn't possible. As a waiter-spinner
|
* is not going to take OSQ lock anyway, there is no need
|
* to call mutex_can_spin_on_owner().
|
*/
|
if (!mutex_can_spin_on_owner(lock))
|
goto fail;
|
|
/*
|
* In order to avoid a stampede of mutex spinners trying to
|
* acquire the mutex all at once, the spinners need to take a
|
* MCS (queued) lock first before spinning on the owner field.
|
*/
|
if (!osq_lock(&lock->osq))
|
goto fail;
|
}
|
|
for (;;) {
|
struct task_struct *owner;
|
|
/* Try to acquire the mutex... */
|
owner = __mutex_trylock_or_owner(lock);
|
if (!owner)
|
break;
|
|
/*
|
* There's an owner, wait for it to either
|
* release the lock or go to sleep.
|
*/
|
if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter))
|
goto fail_unlock;
|
|
/*
|
* 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();
|
}
|
|
if (!waiter)
|
osq_unlock(&lock->osq);
|
|
return true;
|
|
|
fail_unlock:
|
if (!waiter)
|
osq_unlock(&lock->osq);
|
|
fail:
|
/*
|
* If we fell out of the spin path because of need_resched(),
|
* reschedule now, before we try-lock the mutex. This avoids getting
|
* scheduled out right after we obtained the mutex.
|
*/
|
if (need_resched()) {
|
/*
|
* We _should_ have TASK_RUNNING here, but just in case
|
* we do not, make it so, otherwise we might get stuck.
|
*/
|
__set_current_state(TASK_RUNNING);
|
schedule_preempt_disabled();
|
}
|
|
return false;
|
}
|
#else
|
static __always_inline bool
|
mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
|
struct mutex_waiter *waiter)
|
{
|
return false;
|
}
|
#endif
|
|
static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip);
|
|
/**
|
* mutex_unlock - release the mutex
|
* @lock: the mutex to be released
|
*
|
* Unlock a mutex that has been locked by this task previously.
|
*
|
* This function must not be used in interrupt context. Unlocking
|
* of a not locked mutex is not allowed.
|
*
|
* This function is similar to (but not equivalent to) up().
|
*/
|
void __sched mutex_unlock(struct mutex *lock)
|
{
|
trace_android_vh_record_mutex_lock_starttime(current, 0);
|
#ifndef CONFIG_DEBUG_LOCK_ALLOC
|
if (__mutex_unlock_fast(lock))
|
return;
|
#endif
|
__mutex_unlock_slowpath(lock, _RET_IP_);
|
}
|
EXPORT_SYMBOL(mutex_unlock);
|
|
/**
|
* ww_mutex_unlock - release the w/w mutex
|
* @lock: the mutex to be released
|
*
|
* Unlock a mutex that has been locked by this task previously with any of the
|
* ww_mutex_lock* functions (with or without an acquire context). It is
|
* forbidden to release the locks after releasing the acquire context.
|
*
|
* This function must not be used in interrupt context. Unlocking
|
* of a unlocked mutex is not allowed.
|
*/
|
void __sched ww_mutex_unlock(struct ww_mutex *lock)
|
{
|
/*
|
* The unlocking fastpath is the 0->1 transition from 'locked'
|
* into 'unlocked' state:
|
*/
|
if (lock->ctx) {
|
#ifdef CONFIG_DEBUG_MUTEXES
|
DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
|
#endif
|
if (lock->ctx->acquired > 0)
|
lock->ctx->acquired--;
|
lock->ctx = NULL;
|
}
|
|
mutex_unlock(&lock->base);
|
}
|
EXPORT_SYMBOL(ww_mutex_unlock);
|
|
|
static __always_inline int __sched
|
__ww_mutex_kill(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
|
{
|
if (ww_ctx->acquired > 0) {
|
#ifdef CONFIG_DEBUG_MUTEXES
|
struct ww_mutex *ww;
|
|
ww = container_of(lock, struct ww_mutex, base);
|
DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
|
ww_ctx->contending_lock = ww;
|
#endif
|
return -EDEADLK;
|
}
|
|
return 0;
|
}
|
|
|
/*
|
* Check the wound condition for the current lock acquire.
|
*
|
* Wound-Wait: If we're wounded, kill ourself.
|
*
|
* Wait-Die: If we're trying to acquire a lock already held by an older
|
* context, kill ourselves.
|
*
|
* Since __ww_mutex_add_waiter() orders the wait-list on stamp, we only have to
|
* look at waiters before us in the wait-list.
|
*/
|
static inline int __sched
|
__ww_mutex_check_kill(struct mutex *lock, struct mutex_waiter *waiter,
|
struct ww_acquire_ctx *ctx)
|
{
|
struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
|
struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
|
struct mutex_waiter *cur;
|
|
if (ctx->acquired == 0)
|
return 0;
|
|
if (!ctx->is_wait_die) {
|
if (ctx->wounded)
|
return __ww_mutex_kill(lock, ctx);
|
|
return 0;
|
}
|
|
if (hold_ctx && __ww_ctx_stamp_after(ctx, hold_ctx))
|
return __ww_mutex_kill(lock, ctx);
|
|
/*
|
* If there is a waiter in front of us that has a context, then its
|
* stamp is earlier than ours and we must kill ourself.
|
*/
|
cur = waiter;
|
list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) {
|
if (!cur->ww_ctx)
|
continue;
|
|
return __ww_mutex_kill(lock, ctx);
|
}
|
|
return 0;
|
}
|
|
/*
|
* Add @waiter to the wait-list, keep the wait-list ordered by stamp, smallest
|
* first. Such that older contexts are preferred to acquire the lock over
|
* younger contexts.
|
*
|
* Waiters without context are interspersed in FIFO order.
|
*
|
* Furthermore, for Wait-Die kill ourself immediately when possible (there are
|
* older contexts already waiting) to avoid unnecessary waiting and for
|
* Wound-Wait ensure we wound the owning context when it is younger.
|
*/
|
static inline int __sched
|
__ww_mutex_add_waiter(struct mutex_waiter *waiter,
|
struct mutex *lock,
|
struct ww_acquire_ctx *ww_ctx)
|
{
|
struct mutex_waiter *cur;
|
struct list_head *pos;
|
bool is_wait_die;
|
|
if (!ww_ctx) {
|
__mutex_add_waiter(lock, waiter, &lock->wait_list);
|
return 0;
|
}
|
|
is_wait_die = ww_ctx->is_wait_die;
|
|
/*
|
* Add the waiter before the first waiter with a higher stamp.
|
* Waiters without a context are skipped to avoid starving
|
* them. Wait-Die waiters may die here. Wound-Wait waiters
|
* never die here, but they are sorted in stamp order and
|
* may wound the lock holder.
|
*/
|
pos = &lock->wait_list;
|
list_for_each_entry_reverse(cur, &lock->wait_list, list) {
|
if (!cur->ww_ctx)
|
continue;
|
|
if (__ww_ctx_stamp_after(ww_ctx, cur->ww_ctx)) {
|
/*
|
* Wait-Die: if we find an older context waiting, there
|
* is no point in queueing behind it, as we'd have to
|
* die the moment it would acquire the lock.
|
*/
|
if (is_wait_die) {
|
int ret = __ww_mutex_kill(lock, ww_ctx);
|
|
if (ret)
|
return ret;
|
}
|
|
break;
|
}
|
|
pos = &cur->list;
|
|
/* Wait-Die: ensure younger waiters die. */
|
__ww_mutex_die(lock, cur, ww_ctx);
|
}
|
|
__mutex_add_waiter(lock, waiter, pos);
|
|
/*
|
* Wound-Wait: if we're blocking on a mutex owned by a younger context,
|
* wound that such that we might proceed.
|
*/
|
if (!is_wait_die) {
|
struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
|
|
/*
|
* See ww_mutex_set_context_fastpath(). Orders setting
|
* MUTEX_FLAG_WAITERS vs the ww->ctx load,
|
* such that either we or the fastpath will wound @ww->ctx.
|
*/
|
smp_mb();
|
__ww_mutex_wound(lock, ww_ctx, ww->ctx);
|
}
|
|
return 0;
|
}
|
|
/*
|
* Lock a mutex (possibly interruptible), slowpath:
|
*/
|
static __always_inline int __sched
|
__mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
|
struct lockdep_map *nest_lock, unsigned long ip,
|
struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
|
{
|
struct mutex_waiter waiter;
|
struct ww_mutex *ww;
|
int ret;
|
|
if (!use_ww_ctx)
|
ww_ctx = NULL;
|
|
might_sleep();
|
|
#ifdef CONFIG_DEBUG_MUTEXES
|
DEBUG_LOCKS_WARN_ON(lock->magic != lock);
|
#endif
|
|
ww = container_of(lock, struct ww_mutex, base);
|
if (ww_ctx) {
|
if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
|
return -EALREADY;
|
|
/*
|
* Reset the wounded flag after a kill. No other process can
|
* race and wound us here since they can't have a valid owner
|
* pointer if we don't have any locks held.
|
*/
|
if (ww_ctx->acquired == 0)
|
ww_ctx->wounded = 0;
|
}
|
|
preempt_disable();
|
mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
|
|
if (__mutex_trylock(lock) ||
|
mutex_optimistic_spin(lock, ww_ctx, NULL)) {
|
/* got the lock, yay! */
|
lock_acquired(&lock->dep_map, ip);
|
if (ww_ctx)
|
ww_mutex_set_context_fastpath(ww, ww_ctx);
|
trace_android_vh_record_mutex_lock_starttime(current, jiffies);
|
preempt_enable();
|
return 0;
|
}
|
|
spin_lock(&lock->wait_lock);
|
/*
|
* After waiting to acquire the wait_lock, try again.
|
*/
|
if (__mutex_trylock(lock)) {
|
if (ww_ctx)
|
__ww_mutex_check_waiters(lock, ww_ctx);
|
|
goto skip_wait;
|
}
|
|
debug_mutex_lock_common(lock, &waiter);
|
|
lock_contended(&lock->dep_map, ip);
|
|
if (!use_ww_ctx) {
|
/* add waiting tasks to the end of the waitqueue (FIFO): */
|
__mutex_add_waiter(lock, &waiter, &lock->wait_list);
|
|
|
#ifdef CONFIG_DEBUG_MUTEXES
|
waiter.ww_ctx = MUTEX_POISON_WW_CTX;
|
#endif
|
} else {
|
/*
|
* Add in stamp order, waking up waiters that must kill
|
* themselves.
|
*/
|
ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
|
if (ret)
|
goto err_early_kill;
|
|
waiter.ww_ctx = ww_ctx;
|
}
|
|
waiter.task = current;
|
|
trace_android_vh_mutex_wait_start(lock);
|
set_current_state(state);
|
for (;;) {
|
bool first;
|
|
/*
|
* Once we hold wait_lock, we're serialized against
|
* mutex_unlock() handing the lock off to us, do a trylock
|
* before testing the error conditions to make sure we pick up
|
* the handoff.
|
*/
|
if (__mutex_trylock(lock))
|
goto acquired;
|
|
/*
|
* Check for signals and kill conditions while holding
|
* wait_lock. This ensures the lock cancellation is ordered
|
* against mutex_unlock() and wake-ups do not go missing.
|
*/
|
if (signal_pending_state(state, current)) {
|
ret = -EINTR;
|
goto err;
|
}
|
|
if (ww_ctx) {
|
ret = __ww_mutex_check_kill(lock, &waiter, ww_ctx);
|
if (ret)
|
goto err;
|
}
|
|
spin_unlock(&lock->wait_lock);
|
schedule_preempt_disabled();
|
|
first = __mutex_waiter_is_first(lock, &waiter);
|
if (first)
|
__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
|
|
set_current_state(state);
|
/*
|
* Here we order against unlock; we must either see it change
|
* state back to RUNNING and fall through the next schedule(),
|
* or we must see its unlock and acquire.
|
*/
|
if (__mutex_trylock(lock) ||
|
(first && mutex_optimistic_spin(lock, ww_ctx, &waiter)))
|
break;
|
|
spin_lock(&lock->wait_lock);
|
}
|
spin_lock(&lock->wait_lock);
|
acquired:
|
__set_current_state(TASK_RUNNING);
|
trace_android_vh_mutex_wait_finish(lock);
|
|
if (ww_ctx) {
|
/*
|
* Wound-Wait; we stole the lock (!first_waiter), check the
|
* waiters as anyone might want to wound us.
|
*/
|
if (!ww_ctx->is_wait_die &&
|
!__mutex_waiter_is_first(lock, &waiter))
|
__ww_mutex_check_waiters(lock, ww_ctx);
|
}
|
|
__mutex_remove_waiter(lock, &waiter);
|
|
debug_mutex_free_waiter(&waiter);
|
|
skip_wait:
|
/* got the lock - cleanup and rejoice! */
|
lock_acquired(&lock->dep_map, ip);
|
|
if (ww_ctx)
|
ww_mutex_lock_acquired(ww, ww_ctx);
|
|
spin_unlock(&lock->wait_lock);
|
preempt_enable();
|
trace_android_vh_record_mutex_lock_starttime(current, jiffies);
|
return 0;
|
|
err:
|
__set_current_state(TASK_RUNNING);
|
trace_android_vh_mutex_wait_finish(lock);
|
__mutex_remove_waiter(lock, &waiter);
|
err_early_kill:
|
spin_unlock(&lock->wait_lock);
|
debug_mutex_free_waiter(&waiter);
|
mutex_release(&lock->dep_map, ip);
|
preempt_enable();
|
return ret;
|
}
|
|
static int __sched
|
__mutex_lock(struct mutex *lock, long state, unsigned int subclass,
|
struct lockdep_map *nest_lock, unsigned long ip)
|
{
|
return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false);
|
}
|
|
static int __sched
|
__ww_mutex_lock(struct mutex *lock, long state, unsigned int subclass,
|
struct lockdep_map *nest_lock, unsigned long ip,
|
struct ww_acquire_ctx *ww_ctx)
|
{
|
return __mutex_lock_common(lock, state, subclass, nest_lock, ip, ww_ctx, true);
|
}
|
|
#ifdef CONFIG_DEBUG_LOCK_ALLOC
|
void __sched
|
mutex_lock_nested(struct mutex *lock, unsigned int subclass)
|
{
|
__mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
|
}
|
|
EXPORT_SYMBOL_GPL(mutex_lock_nested);
|
|
void __sched
|
_mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
|
{
|
__mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_);
|
}
|
EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
|
|
int __sched
|
mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
|
{
|
return __mutex_lock(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_);
|
}
|
EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
|
|
int __sched
|
mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
|
{
|
return __mutex_lock(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_);
|
}
|
EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
|
|
void __sched
|
mutex_lock_io_nested(struct mutex *lock, unsigned int subclass)
|
{
|
int token;
|
|
might_sleep();
|
|
token = io_schedule_prepare();
|
__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
|
subclass, NULL, _RET_IP_, NULL, 0);
|
io_schedule_finish(token);
|
}
|
EXPORT_SYMBOL_GPL(mutex_lock_io_nested);
|
|
static inline int
|
ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
|
{
|
#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
|
unsigned tmp;
|
|
if (ctx->deadlock_inject_countdown-- == 0) {
|
tmp = ctx->deadlock_inject_interval;
|
if (tmp > UINT_MAX/4)
|
tmp = UINT_MAX;
|
else
|
tmp = tmp*2 + tmp + tmp/2;
|
|
ctx->deadlock_inject_interval = tmp;
|
ctx->deadlock_inject_countdown = tmp;
|
ctx->contending_lock = lock;
|
|
ww_mutex_unlock(lock);
|
|
return -EDEADLK;
|
}
|
#endif
|
|
return 0;
|
}
|
|
int __sched
|
ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
|
{
|
int ret;
|
|
might_sleep();
|
ret = __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE,
|
0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
|
ctx);
|
if (!ret && ctx && ctx->acquired > 1)
|
return ww_mutex_deadlock_injection(lock, ctx);
|
|
return ret;
|
}
|
EXPORT_SYMBOL_GPL(ww_mutex_lock);
|
|
int __sched
|
ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
|
{
|
int ret;
|
|
might_sleep();
|
ret = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE,
|
0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
|
ctx);
|
|
if (!ret && ctx && ctx->acquired > 1)
|
return ww_mutex_deadlock_injection(lock, ctx);
|
|
return ret;
|
}
|
EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);
|
|
#endif
|
|
/*
|
* Release the lock, slowpath:
|
*/
|
static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
|
{
|
struct task_struct *next = NULL;
|
DEFINE_WAKE_Q(wake_q);
|
unsigned long owner;
|
|
mutex_release(&lock->dep_map, ip);
|
|
/*
|
* Release the lock before (potentially) taking the spinlock such that
|
* other contenders can get on with things ASAP.
|
*
|
* Except when HANDOFF, in that case we must not clear the owner field,
|
* but instead set it to the top waiter.
|
*/
|
owner = atomic_long_read(&lock->owner);
|
for (;;) {
|
unsigned long old;
|
|
#ifdef CONFIG_DEBUG_MUTEXES
|
DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
|
DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
|
#endif
|
|
if (owner & MUTEX_FLAG_HANDOFF)
|
break;
|
|
old = atomic_long_cmpxchg_release(&lock->owner, owner,
|
__owner_flags(owner));
|
if (old == owner) {
|
if (owner & MUTEX_FLAG_WAITERS)
|
break;
|
|
return;
|
}
|
|
owner = old;
|
}
|
|
spin_lock(&lock->wait_lock);
|
debug_mutex_unlock(lock);
|
if (!list_empty(&lock->wait_list)) {
|
/* get the first entry from the wait-list: */
|
struct mutex_waiter *waiter =
|
list_first_entry(&lock->wait_list,
|
struct mutex_waiter, list);
|
|
next = waiter->task;
|
|
debug_mutex_wake_waiter(lock, waiter);
|
wake_q_add(&wake_q, next);
|
}
|
|
if (owner & MUTEX_FLAG_HANDOFF)
|
__mutex_handoff(lock, next);
|
|
trace_android_vh_mutex_unlock_slowpath(lock);
|
spin_unlock(&lock->wait_lock);
|
|
wake_up_q(&wake_q);
|
trace_android_vh_mutex_unlock_slowpath_end(lock, next);
|
}
|
|
#ifndef CONFIG_DEBUG_LOCK_ALLOC
|
/*
|
* Here come the less common (and hence less performance-critical) APIs:
|
* mutex_lock_interruptible() and mutex_trylock().
|
*/
|
static noinline int __sched
|
__mutex_lock_killable_slowpath(struct mutex *lock);
|
|
static noinline int __sched
|
__mutex_lock_interruptible_slowpath(struct mutex *lock);
|
|
/**
|
* mutex_lock_interruptible() - Acquire the mutex, interruptible by signals.
|
* @lock: The mutex to be acquired.
|
*
|
* Lock the mutex like mutex_lock(). If a signal is delivered while the
|
* process is sleeping, this function will return without acquiring the
|
* mutex.
|
*
|
* Context: Process context.
|
* Return: 0 if the lock was successfully acquired or %-EINTR if a
|
* signal arrived.
|
*/
|
int __sched mutex_lock_interruptible(struct mutex *lock)
|
{
|
might_sleep();
|
|
if (__mutex_trylock_fast(lock))
|
return 0;
|
|
return __mutex_lock_interruptible_slowpath(lock);
|
}
|
|
EXPORT_SYMBOL(mutex_lock_interruptible);
|
|
/**
|
* mutex_lock_killable() - Acquire the mutex, interruptible by fatal signals.
|
* @lock: The mutex to be acquired.
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*
|
* Lock the mutex like mutex_lock(). If a signal which will be fatal to
|
* the current process is delivered while the process is sleeping, this
|
* function will return without acquiring the mutex.
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*
|
* Context: Process context.
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* Return: 0 if the lock was successfully acquired or %-EINTR if a
|
* fatal signal arrived.
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*/
|
int __sched mutex_lock_killable(struct mutex *lock)
|
{
|
might_sleep();
|
|
if (__mutex_trylock_fast(lock))
|
return 0;
|
|
return __mutex_lock_killable_slowpath(lock);
|
}
|
EXPORT_SYMBOL(mutex_lock_killable);
|
|
/**
|
* mutex_lock_io() - Acquire the mutex and mark the process as waiting for I/O
|
* @lock: The mutex to be acquired.
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*
|
* Lock the mutex like mutex_lock(). While the task is waiting for this
|
* mutex, it will be accounted as being in the IO wait state by the
|
* scheduler.
|
*
|
* Context: Process context.
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*/
|
void __sched mutex_lock_io(struct mutex *lock)
|
{
|
int token;
|
|
token = io_schedule_prepare();
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mutex_lock(lock);
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io_schedule_finish(token);
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}
|
EXPORT_SYMBOL_GPL(mutex_lock_io);
|
|
static noinline void __sched
|
__mutex_lock_slowpath(struct mutex *lock)
|
{
|
__mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
|
}
|
|
static noinline int __sched
|
__mutex_lock_killable_slowpath(struct mutex *lock)
|
{
|
return __mutex_lock(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);
|
}
|
|
static noinline int __sched
|
__mutex_lock_interruptible_slowpath(struct mutex *lock)
|
{
|
return __mutex_lock(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);
|
}
|
|
static noinline int __sched
|
__ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
|
{
|
return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0, NULL,
|
_RET_IP_, ctx);
|
}
|
|
static noinline int __sched
|
__ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
|
struct ww_acquire_ctx *ctx)
|
{
|
return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0, NULL,
|
_RET_IP_, ctx);
|
}
|
|
#endif
|
|
/**
|
* mutex_trylock - try to acquire the mutex, without waiting
|
* @lock: the mutex to be acquired
|
*
|
* Try to acquire the mutex atomically. Returns 1 if the mutex
|
* has been acquired successfully, and 0 on contention.
|
*
|
* NOTE: this function follows the spin_trylock() convention, so
|
* it is negated from the down_trylock() return values! Be careful
|
* about this when converting semaphore users to mutexes.
|
*
|
* This function must not be used in interrupt context. The
|
* mutex must be released by the same task that acquired it.
|
*/
|
int __sched mutex_trylock(struct mutex *lock)
|
{
|
bool locked;
|
|
#ifdef CONFIG_DEBUG_MUTEXES
|
DEBUG_LOCKS_WARN_ON(lock->magic != lock);
|
#endif
|
|
locked = __mutex_trylock(lock);
|
if (locked) {
|
trace_android_vh_record_mutex_lock_starttime(current, jiffies);
|
mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
|
}
|
|
return locked;
|
}
|
EXPORT_SYMBOL(mutex_trylock);
|
|
#ifndef CONFIG_DEBUG_LOCK_ALLOC
|
int __sched
|
ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
|
{
|
might_sleep();
|
|
if (__mutex_trylock_fast(&lock->base)) {
|
if (ctx)
|
ww_mutex_set_context_fastpath(lock, ctx);
|
return 0;
|
}
|
|
return __ww_mutex_lock_slowpath(lock, ctx);
|
}
|
EXPORT_SYMBOL(ww_mutex_lock);
|
|
int __sched
|
ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
|
{
|
might_sleep();
|
|
if (__mutex_trylock_fast(&lock->base)) {
|
if (ctx)
|
ww_mutex_set_context_fastpath(lock, ctx);
|
return 0;
|
}
|
|
return __ww_mutex_lock_interruptible_slowpath(lock, ctx);
|
}
|
EXPORT_SYMBOL(ww_mutex_lock_interruptible);
|
|
#endif
|
|
/**
|
* atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
|
* @cnt: the atomic which we are to dec
|
* @lock: the mutex to return holding if we dec to 0
|
*
|
* return true and hold lock if we dec to 0, return false otherwise
|
*/
|
int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
|
{
|
/* dec if we can't possibly hit 0 */
|
if (atomic_add_unless(cnt, -1, 1))
|
return 0;
|
/* we might hit 0, so take the lock */
|
mutex_lock(lock);
|
if (!atomic_dec_and_test(cnt)) {
|
/* when we actually did the dec, we didn't hit 0 */
|
mutex_unlock(lock);
|
return 0;
|
}
|
/* we hit 0, and we hold the lock */
|
return 1;
|
}
|
EXPORT_SYMBOL(atomic_dec_and_mutex_lock);
|
