diff options
author | Peter Zijlstra <peterz@infradead.org> | 2017-03-22 11:35:58 +0100 |
---|---|---|
committer | Thomas Gleixner <tglx@linutronix.de> | 2017-03-23 19:10:09 +0100 |
commit | cfafcd117da0216520568c195cb2f6cd1980c4bb (patch) | |
tree | cce98f12a6bfa27515fb1cabc5bbd6fd55a8459f /kernel/locking/rtmutex.c | |
parent | 38d589f2fd08f1296aea3ce62bebd185125c6d81 (diff) | |
download | linux-cfafcd117da0216520568c195cb2f6cd1980c4bb.tar.bz2 |
futex: Rework futex_lock_pi() to use rt_mutex_*_proxy_lock()
By changing futex_lock_pi() to use rt_mutex_*_proxy_lock() all wait_list
modifications are done under both hb->lock and wait_lock.
This closes the obvious interleave pattern between futex_lock_pi() and
futex_unlock_pi(), but not entirely so. See below:
Before:
futex_lock_pi() futex_unlock_pi()
unlock hb->lock
lock hb->lock
unlock hb->lock
lock rt_mutex->wait_lock
unlock rt_mutex_wait_lock
-EAGAIN
lock rt_mutex->wait_lock
list_add
unlock rt_mutex->wait_lock
schedule()
lock rt_mutex->wait_lock
list_del
unlock rt_mutex->wait_lock
<idem>
-EAGAIN
lock hb->lock
After:
futex_lock_pi() futex_unlock_pi()
lock hb->lock
lock rt_mutex->wait_lock
list_add
unlock rt_mutex->wait_lock
unlock hb->lock
schedule()
lock hb->lock
unlock hb->lock
lock hb->lock
lock rt_mutex->wait_lock
list_del
unlock rt_mutex->wait_lock
lock rt_mutex->wait_lock
unlock rt_mutex_wait_lock
-EAGAIN
unlock hb->lock
It does however solve the earlier starvation/live-lock scenario which got
introduced with the -EAGAIN since unlike the before scenario; where the
-EAGAIN happens while futex_unlock_pi() doesn't hold any locks; in the
after scenario it happens while futex_unlock_pi() actually holds a lock,
and then it is serialized on that lock.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104152.062785528@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/locking/rtmutex.c')
-rw-r--r-- | kernel/locking/rtmutex.c | 26 |
1 files changed, 7 insertions, 19 deletions
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 1e8368db276e..48418a1733b8 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1493,19 +1493,6 @@ int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock) EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible); /* - * Futex variant with full deadlock detection. - * Futex variants must not use the fast-path, see __rt_mutex_futex_unlock(). - */ -int __sched rt_mutex_timed_futex_lock(struct rt_mutex *lock, - struct hrtimer_sleeper *timeout) -{ - might_sleep(); - - return rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, - timeout, RT_MUTEX_FULL_CHAINWALK); -} - -/* * Futex variant, must not use fastpath. */ int __sched rt_mutex_futex_trylock(struct rt_mutex *lock) @@ -1782,12 +1769,6 @@ int rt_mutex_wait_proxy_lock(struct rt_mutex *lock, /* sleep on the mutex */ ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter); - /* - * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might - * have to fix that up. - */ - fixup_rt_mutex_waiters(lock); - raw_spin_unlock_irq(&lock->wait_lock); return ret; @@ -1827,6 +1808,13 @@ bool rt_mutex_cleanup_proxy_lock(struct rt_mutex *lock, fixup_rt_mutex_waiters(lock); cleanup = true; } + + /* + * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might + * have to fix that up. + */ + fixup_rt_mutex_waiters(lock); + raw_spin_unlock_irq(&lock->wait_lock); return cleanup; |