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Diffstat (limited to 'kernel/locking/rtmutex.c')
-rw-r--r--kernel/locking/rtmutex.c55
1 files changed, 46 insertions, 9 deletions
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 7779ee8abc2a..010cf4e6d0b8 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -89,15 +89,31 @@ static inline int __ww_mutex_check_kill(struct rt_mutex *lock,
* set this bit before looking at the lock.
*/
-static __always_inline void
-rt_mutex_set_owner(struct rt_mutex_base *lock, struct task_struct *owner)
+static __always_inline struct task_struct *
+rt_mutex_owner_encode(struct rt_mutex_base *lock, struct task_struct *owner)
{
unsigned long val = (unsigned long)owner;
if (rt_mutex_has_waiters(lock))
val |= RT_MUTEX_HAS_WAITERS;
- WRITE_ONCE(lock->owner, (struct task_struct *)val);
+ return (struct task_struct *)val;
+}
+
+static __always_inline void
+rt_mutex_set_owner(struct rt_mutex_base *lock, struct task_struct *owner)
+{
+ /*
+ * lock->wait_lock is held but explicit acquire semantics are needed
+ * for a new lock owner so WRITE_ONCE is insufficient.
+ */
+ xchg_acquire(&lock->owner, rt_mutex_owner_encode(lock, owner));
+}
+
+static __always_inline void rt_mutex_clear_owner(struct rt_mutex_base *lock)
+{
+ /* lock->wait_lock is held so the unlock provides release semantics. */
+ WRITE_ONCE(lock->owner, rt_mutex_owner_encode(lock, NULL));
}
static __always_inline void clear_rt_mutex_waiters(struct rt_mutex_base *lock)
@@ -106,7 +122,8 @@ static __always_inline void clear_rt_mutex_waiters(struct rt_mutex_base *lock)
((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
}
-static __always_inline void fixup_rt_mutex_waiters(struct rt_mutex_base *lock)
+static __always_inline void
+fixup_rt_mutex_waiters(struct rt_mutex_base *lock, bool acquire_lock)
{
unsigned long owner, *p = (unsigned long *) &lock->owner;
@@ -172,8 +189,21 @@ static __always_inline void fixup_rt_mutex_waiters(struct rt_mutex_base *lock)
* still set.
*/
owner = READ_ONCE(*p);
- if (owner & RT_MUTEX_HAS_WAITERS)
- WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
+ if (owner & RT_MUTEX_HAS_WAITERS) {
+ /*
+ * See rt_mutex_set_owner() and rt_mutex_clear_owner() on
+ * why xchg_acquire() is used for updating owner for
+ * locking and WRITE_ONCE() for unlocking.
+ *
+ * WRITE_ONCE() would work for the acquire case too, but
+ * in case that the lock acquisition failed it might
+ * force other lockers into the slow path unnecessarily.
+ */
+ if (acquire_lock)
+ xchg_acquire(p, owner & ~RT_MUTEX_HAS_WAITERS);
+ else
+ WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
+ }
}
/*
@@ -208,6 +238,13 @@ static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
owner = *p;
} while (cmpxchg_relaxed(p, owner,
owner | RT_MUTEX_HAS_WAITERS) != owner);
+
+ /*
+ * The cmpxchg loop above is relaxed to avoid back-to-back ACQUIRE
+ * operations in the event of contention. Ensure the successful
+ * cmpxchg is visible.
+ */
+ smp_mb__after_atomic();
}
/*
@@ -1243,7 +1280,7 @@ static int __sched __rt_mutex_slowtrylock(struct rt_mutex_base *lock)
* try_to_take_rt_mutex() sets the lock waiters bit
* unconditionally. Clean this up.
*/
- fixup_rt_mutex_waiters(lock);
+ fixup_rt_mutex_waiters(lock, true);
return ret;
}
@@ -1604,7 +1641,7 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
* try_to_take_rt_mutex() sets the waiter bit
* unconditionally. We might have to fix that up.
*/
- fixup_rt_mutex_waiters(lock);
+ fixup_rt_mutex_waiters(lock, true);
trace_contention_end(lock, ret);
@@ -1719,7 +1756,7 @@ static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock)
* try_to_take_rt_mutex() sets the waiter bit unconditionally.
* We might have to fix that up:
*/
- fixup_rt_mutex_waiters(lock);
+ fixup_rt_mutex_waiters(lock, true);
debug_rt_mutex_free_waiter(&waiter);
trace_contention_end(lock, 0);