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| -rw-r--r-- | Documentation/locking/mutex-design.rst | 6 | ||||
| -rw-r--r-- | kernel/locking/mutex.c | 5 |
2 files changed, 11 insertions, 0 deletions
diff --git a/Documentation/locking/mutex-design.rst b/Documentation/locking/mutex-design.rst index 78540cd7f54b..7572339b2f12 100644 --- a/Documentation/locking/mutex-design.rst +++ b/Documentation/locking/mutex-design.rst @@ -101,6 +101,12 @@ features that make lock debugging easier and faster: - Detects multi-task circular deadlocks and prints out all affected locks and tasks (and only those tasks). +Releasing a mutex is not an atomic operation: Once a mutex release operation +has begun, another context may be able to acquire the mutex before the release +operation has fully completed. The mutex user must ensure that the mutex is not +destroyed while a release operation is still in progress - in other words, +callers of mutex_unlock() must ensure that the mutex stays alive until +mutex_unlock() has returned. Interfaces ---------- diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 2deeeca3e71b..cbae8c0b89ab 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -532,6 +532,11 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne * This function must not be used in interrupt context. Unlocking * of a not locked mutex is not allowed. * + * The caller must ensure that the mutex stays alive until this function has + * returned - mutex_unlock() can NOT directly be used to release an object such + * that another concurrent task can free it. + * Mutexes are different from spinlocks & refcounts in this aspect. + * * This function is similar to (but not equivalent to) up(). */ void __sched mutex_unlock(struct mutex *lock) |