v4.19.13 snapshot.
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
new file mode 100644
index 0000000..3f8a351
--- /dev/null
+++ b/kernel/locking/mutex.c
@@ -0,0 +1,1445 @@
+/*
+ * kernel/locking/mutex.c
+ *
+ * Mutexes: blocking mutual exclusion locks
+ *
+ * Started by Ingo Molnar:
+ *
+ * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
+ *
+ * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
+ * David Howells for suggestions and improvements.
+ *
+ * - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline
+ * from the -rt tree, where it was originally implemented for rtmutexes
+ * by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale
+ * and Sven Dietrich.
+ *
+ * Also see Documentation/locking/mutex-design.txt.
+ */
+#include <linux/mutex.h>
+#include <linux/ww_mutex.h>
+#include <linux/sched/signal.h>
+#include <linux/sched/rt.h>
+#include <linux/sched/wake_q.h>
+#include <linux/sched/debug.h>
+#include <linux/export.h>
+#include <linux/spinlock.h>
+#include <linux/interrupt.h>
+#include <linux/debug_locks.h>
+#include <linux/osq_lock.h>
+
+#ifdef CONFIG_DEBUG_MUTEXES
+# include "mutex-debug.h"
+#else
+# include "mutex.h"
+#endif
+
+void
+__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
+{
+ atomic_long_set(&lock->owner, 0);
+ spin_lock_init(&lock->wait_lock);
+ INIT_LIST_HEAD(&lock->wait_list);
+#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
+ osq_lock_init(&lock->osq);
+#endif
+
+ debug_mutex_init(lock, name, key);
+}
+EXPORT_SYMBOL(__mutex_init);
+
+/*
+ * @owner: contains: 'struct task_struct *' to the current lock owner,
+ * NULL means not owned. Since task_struct pointers are aligned at
+ * at least L1_CACHE_BYTES, we have low bits to store extra state.
+ *
+ * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
+ * Bit1 indicates unlock needs to hand the lock to the top-waiter
+ * Bit2 indicates handoff has been done and we're waiting for pickup.
+ */
+#define MUTEX_FLAG_WAITERS 0x01
+#define MUTEX_FLAG_HANDOFF 0x02
+#define MUTEX_FLAG_PICKUP 0x04
+
+#define MUTEX_FLAGS 0x07
+
+static inline struct task_struct *__owner_task(unsigned long owner)
+{
+ return (struct task_struct *)(owner & ~MUTEX_FLAGS);
+}
+
+static inline unsigned long __owner_flags(unsigned long owner)
+{
+ return owner & MUTEX_FLAGS;
+}
+
+/*
+ * Trylock variant that retuns the owning task on failure.
+ */
+static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
+{
+ unsigned long owner, curr = (unsigned long)current;
+
+ owner = atomic_long_read(&lock->owner);
+ for (;;) { /* must loop, can race against a flag */
+ unsigned long old, flags = __owner_flags(owner);
+ unsigned long task = owner & ~MUTEX_FLAGS;
+
+ if (task) {
+ if (likely(task != curr))
+ break;
+
+ if (likely(!(flags & MUTEX_FLAG_PICKUP)))
+ break;
+
+ flags &= ~MUTEX_FLAG_PICKUP;
+ } else {
+#ifdef CONFIG_DEBUG_MUTEXES
+ DEBUG_LOCKS_WARN_ON(flags & MUTEX_FLAG_PICKUP);
+#endif
+ }
+
+ /*
+ * We set the HANDOFF bit, we must make sure it doesn't live
+ * past the point where we acquire it. This would be possible
+ * if we (accidentally) set the bit on an unlocked mutex.
+ */
+ flags &= ~MUTEX_FLAG_HANDOFF;
+
+ old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags);
+ if (old == owner)
+ return NULL;
+
+ owner = old;
+ }
+
+ return __owner_task(owner);
+}
+
+/*
+ * Actual trylock that will work on any unlocked state.
+ */
+static inline bool __mutex_trylock(struct mutex *lock)
+{
+ return !__mutex_trylock_or_owner(lock);
+}
+
+#ifndef CONFIG_DEBUG_LOCK_ALLOC
+/*
+ * Lockdep annotations are contained to the slow paths for simplicity.
+ * There is nothing that would stop spreading the lockdep annotations outwards
+ * except more code.
+ */
+
+/*
+ * Optimistic trylock that only works in the uncontended case. Make sure to
+ * follow with a __mutex_trylock() before failing.
+ */
+static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
+{
+ unsigned long curr = (unsigned long)current;
+ unsigned long zero = 0UL;
+
+ if (atomic_long_try_cmpxchg_acquire(&lock->owner, &zero, curr))
+ return true;
+
+ return false;
+}
+
+static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
+{
+ unsigned long curr = (unsigned long)current;
+
+ if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr)
+ return true;
+
+ return false;
+}
+#endif
+
+static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
+{
+ atomic_long_or(flag, &lock->owner);
+}
+
+static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag)
+{
+ atomic_long_andnot(flag, &lock->owner);
+}
+
+static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter)
+{
+ return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
+}
+
+/*
+ * Add @waiter to a given location in the lock wait_list and set the
+ * FLAG_WAITERS flag if it's the first waiter.
+ */
+static void __sched
+__mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
+ struct list_head *list)
+{
+ debug_mutex_add_waiter(lock, waiter, current);
+
+ list_add_tail(&waiter->list, list);
+ if (__mutex_waiter_is_first(lock, waiter))
+ __mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
+}
+
+/*
+ * Give up ownership to a specific task, when @task = NULL, this is equivalent
+ * to a regular unlock. Sets PICKUP on a handoff, clears HANDOF, preserves
+ * WAITERS. Provides RELEASE semantics like a regular unlock, the
+ * __mutex_trylock() provides a matching ACQUIRE semantics for the handoff.
+ */
+static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
+{
+ unsigned long owner = atomic_long_read(&lock->owner);
+
+ for (;;) {
+ unsigned long old, new;
+
+#ifdef CONFIG_DEBUG_MUTEXES
+ DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
+ DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
+#endif
+
+ new = (owner & MUTEX_FLAG_WAITERS);
+ new |= (unsigned long)task;
+ if (task)
+ new |= MUTEX_FLAG_PICKUP;
+
+ old = atomic_long_cmpxchg_release(&lock->owner, owner, new);
+ if (old == owner)
+ break;
+
+ owner = old;
+ }
+}
+
+#ifndef CONFIG_DEBUG_LOCK_ALLOC
+/*
+ * We split the mutex lock/unlock logic into separate fastpath and
+ * slowpath functions, to reduce the register pressure on the fastpath.
+ * We also put the fastpath first in the kernel image, to make sure the
+ * branch is predicted by the CPU as default-untaken.
+ */
+static void __sched __mutex_lock_slowpath(struct mutex *lock);
+
+/**
+ * mutex_lock - acquire the mutex
+ * @lock: the mutex to be acquired
+ *
+ * Lock the mutex exclusively for this task. If the mutex is not
+ * available right now, it will sleep until it can get it.
+ *
+ * The mutex must later on be released by the same task that
+ * acquired it. Recursive locking is not allowed. The task
+ * may not exit without first unlocking the mutex. Also, kernel
+ * memory where the mutex resides must not be freed with
+ * the mutex still locked. The mutex must first be initialized
+ * (or statically defined) before it can be locked. memset()-ing
+ * the mutex to 0 is not allowed.
+ *
+ * (The CONFIG_DEBUG_MUTEXES .config option turns on debugging
+ * checks that will enforce the restrictions and will also do
+ * deadlock debugging)
+ *
+ * This function is similar to (but not equivalent to) down().
+ */
+void __sched mutex_lock(struct mutex *lock)
+{
+ might_sleep();
+
+ if (!__mutex_trylock_fast(lock))
+ __mutex_lock_slowpath(lock);
+}
+EXPORT_SYMBOL(mutex_lock);
+#endif
+
+/*
+ * Wait-Die:
+ * The newer transactions are killed when:
+ * It (the new transaction) makes a request for a lock being held
+ * by an older transaction.
+ *
+ * Wound-Wait:
+ * The newer transactions are wounded when:
+ * An older transaction makes a request for a lock being held by
+ * the newer transaction.
+ */
+
+/*
+ * Associate the ww_mutex @ww with the context @ww_ctx under which we acquired
+ * it.
+ */
+static __always_inline void
+ww_mutex_lock_acquired(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
+{
+#ifdef CONFIG_DEBUG_MUTEXES
+ /*
+ * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
+ * but released with a normal mutex_unlock in this call.
+ *
+ * This should never happen, always use ww_mutex_unlock.
+ */
+ DEBUG_LOCKS_WARN_ON(ww->ctx);
+
+ /*
+ * Not quite done after calling ww_acquire_done() ?
+ */
+ DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
+
+ if (ww_ctx->contending_lock) {
+ /*
+ * After -EDEADLK you tried to
+ * acquire a different ww_mutex? Bad!
+ */
+ DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
+
+ /*
+ * You called ww_mutex_lock after receiving -EDEADLK,
+ * but 'forgot' to unlock everything else first?
+ */
+ DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
+ ww_ctx->contending_lock = NULL;
+ }
+
+ /*
+ * Naughty, using a different class will lead to undefined behavior!
+ */
+ DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
+#endif
+ ww_ctx->acquired++;
+ ww->ctx = ww_ctx;
+}
+
+/*
+ * Determine if context @a is 'after' context @b. IOW, @a is a younger
+ * transaction than @b and depending on algorithm either needs to wait for
+ * @b or die.
+ */
+static inline bool __sched
+__ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
+{
+
+ return (signed long)(a->stamp - b->stamp) > 0;
+}
+
+/*
+ * Wait-Die; wake a younger waiter context (when locks held) such that it can
+ * die.
+ *
+ * Among waiters with context, only the first one can have other locks acquired
+ * already (ctx->acquired > 0), because __ww_mutex_add_waiter() and
+ * __ww_mutex_check_kill() wake any but the earliest context.
+ */
+static bool __sched
+__ww_mutex_die(struct mutex *lock, struct mutex_waiter *waiter,
+ struct ww_acquire_ctx *ww_ctx)
+{
+ if (!ww_ctx->is_wait_die)
+ return false;
+
+ if (waiter->ww_ctx->acquired > 0 &&
+ __ww_ctx_stamp_after(waiter->ww_ctx, ww_ctx)) {
+ debug_mutex_wake_waiter(lock, waiter);
+ wake_up_process(waiter->task);
+ }
+
+ return true;
+}
+
+/*
+ * Wound-Wait; wound a younger @hold_ctx if it holds the lock.
+ *
+ * Wound the lock holder if there are waiters with older transactions than
+ * the lock holders. Even if multiple waiters may wound the lock holder,
+ * it's sufficient that only one does.
+ */
+static bool __ww_mutex_wound(struct mutex *lock,
+ struct ww_acquire_ctx *ww_ctx,
+ struct ww_acquire_ctx *hold_ctx)
+{
+ struct task_struct *owner = __mutex_owner(lock);
+
+ lockdep_assert_held(&lock->wait_lock);
+
+ /*
+ * Possible through __ww_mutex_add_waiter() when we race with
+ * ww_mutex_set_context_fastpath(). In that case we'll get here again
+ * through __ww_mutex_check_waiters().
+ */
+ if (!hold_ctx)
+ return false;
+
+ /*
+ * Can have !owner because of __mutex_unlock_slowpath(), but if owner,
+ * it cannot go away because we'll have FLAG_WAITERS set and hold
+ * wait_lock.
+ */
+ if (!owner)
+ return false;
+
+ if (ww_ctx->acquired > 0 && __ww_ctx_stamp_after(hold_ctx, ww_ctx)) {
+ hold_ctx->wounded = 1;
+
+ /*
+ * wake_up_process() paired with set_current_state()
+ * inserts sufficient barriers to make sure @owner either sees
+ * it's wounded in __ww_mutex_check_kill() or has a
+ * wakeup pending to re-read the wounded state.
+ */
+ if (owner != current)
+ wake_up_process(owner);
+
+ return true;
+ }
+
+ return false;
+}
+
+/*
+ * We just acquired @lock under @ww_ctx, if there are later contexts waiting
+ * behind us on the wait-list, check if they need to die, or wound us.
+ *
+ * See __ww_mutex_add_waiter() for the list-order construction; basically the
+ * list is ordered by stamp, smallest (oldest) first.
+ *
+ * This relies on never mixing wait-die/wound-wait on the same wait-list;
+ * which is currently ensured by that being a ww_class property.
+ *
+ * The current task must not be on the wait list.
+ */
+static void __sched
+__ww_mutex_check_waiters(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
+{
+ struct mutex_waiter *cur;
+
+ lockdep_assert_held(&lock->wait_lock);
+
+ list_for_each_entry(cur, &lock->wait_list, list) {
+ if (!cur->ww_ctx)
+ continue;
+
+ if (__ww_mutex_die(lock, cur, ww_ctx) ||
+ __ww_mutex_wound(lock, cur->ww_ctx, ww_ctx))
+ break;
+ }
+}
+
+/*
+ * After acquiring lock with fastpath, where we do not hold wait_lock, set ctx
+ * and wake up any waiters so they can recheck.
+ */
+static __always_inline void
+ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
+{
+ ww_mutex_lock_acquired(lock, ctx);
+
+ /*
+ * The lock->ctx update should be visible on all cores before
+ * the WAITERS check is done, otherwise contended waiters might be
+ * 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. */
+
+ /*
+ * [W] ww->ctx = ctx [W] MUTEX_FLAG_WAITERS
+ * MB MB
+ * [R] MUTEX_FLAG_WAITERS [R] ww->ctx
+ *
+ * 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
+ * die or wound us.
+ */
+ spin_lock(&lock->base.wait_lock);
+ __ww_mutex_check_waiters(&lock->base, ctx);
+ spin_unlock(&lock->base.wait_lock);
+}
+
+#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
+
+static inline
+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,
+ const bool use_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,
+ const bool use_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)
+{
+#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;
+ bool first = false;
+ struct ww_mutex *ww;
+ int ret;
+
+ might_sleep();
+
+ ww = container_of(lock, struct ww_mutex, base);
+ if (use_ww_ctx && 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, use_ww_ctx, NULL)) {
+ /* got the lock, yay! */
+ lock_acquired(&lock->dep_map, ip);
+ if (use_ww_ctx && ww_ctx)
+ ww_mutex_set_context_fastpath(ww, ww_ctx);
+ preempt_enable();
+ return 0;
+ }
+
+ spin_lock(&lock->wait_lock);
+ /*
+ * After waiting to acquire the wait_lock, try again.
+ */
+ if (__mutex_trylock(lock)) {
+ if (use_ww_ctx && 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;
+
+ set_current_state(state);
+ for (;;) {
+ /*
+ * 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 (unlikely(signal_pending_state(state, current))) {
+ ret = -EINTR;
+ goto err;
+ }
+
+ if (use_ww_ctx && ww_ctx) {
+ ret = __ww_mutex_check_kill(lock, &waiter, ww_ctx);
+ if (ret)
+ goto err;
+ }
+
+ spin_unlock(&lock->wait_lock);
+ schedule_preempt_disabled();
+
+ /*
+ * ww_mutex needs to always recheck its position since its waiter
+ * list is not FIFO ordered.
+ */
+ if ((use_ww_ctx && ww_ctx) || !first) {
+ 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, use_ww_ctx, &waiter)))
+ break;
+
+ spin_lock(&lock->wait_lock);
+ }
+ spin_lock(&lock->wait_lock);
+acquired:
+ __set_current_state(TASK_RUNNING);
+
+ if (use_ww_ctx && 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, current);
+ if (likely(list_empty(&lock->wait_list)))
+ __mutex_clear_flag(lock, MUTEX_FLAGS);
+
+ debug_mutex_free_waiter(&waiter);
+
+skip_wait:
+ /* got the lock - cleanup and rejoice! */
+ lock_acquired(&lock->dep_map, ip);
+
+ if (use_ww_ctx && ww_ctx)
+ ww_mutex_lock_acquired(ww, ww_ctx);
+
+ spin_unlock(&lock->wait_lock);
+ preempt_enable();
+ return 0;
+
+err:
+ __set_current_state(TASK_RUNNING);
+ mutex_remove_waiter(lock, &waiter, current);
+err_early_kill:
+ spin_unlock(&lock->wait_lock);
+ debug_mutex_free_waiter(&waiter);
+ mutex_release(&lock->dep_map, 1, 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, 1, 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);
+
+ spin_unlock(&lock->wait_lock);
+
+ wake_up_q(&wake_q);
+}
+
+#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.
+ *
+ * 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.
+ *
+ * Context: Process context.
+ * Return: 0 if the lock was successfully acquired or %-EINTR if a
+ * fatal signal arrived.
+ */
+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.
+ *
+ * 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.
+ */
+void __sched mutex_lock_io(struct mutex *lock)
+{
+ int token;
+
+ token = io_schedule_prepare();
+ mutex_lock(lock);
+ io_schedule_finish(token);
+}
+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 = __mutex_trylock(lock);
+
+ if (locked)
+ 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);