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| author | Peter Zijlstra <peterz@infradead.org> | 2018-03-27 14:14:38 +0200 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2018-03-28 23:01:30 +0200 |
| commit | c28d62cf52d791ba5f6db7ce525ed06b86291c82 (patch) | |
| tree | 683f0b9f5b8faa613a46da023b1b7a4bd204c33e /kernel/locking | |
| parent | ac605bee0bfab40fd5d11964705e907d2d5a32de (diff) | |
| download | linux-0-day-c28d62cf52d791ba5f6db7ce525ed06b86291c82.tar.gz linux-0-day-c28d62cf52d791ba5f6db7ce525ed06b86291c82.tar.xz | |
locking/rtmutex: Handle non enqueued waiters gracefully in remove_waiter()
In -RT task_blocks_on_rt_mutex() may return with -EAGAIN due to
(->pi_blocked_on == PI_WAKEUP_INPROGRESS) before it added itself as a
waiter. In such a case remove_waiter() must not be called because without a
waiter it will trigger the BUG_ON() statement.
This was initially reported by Yimin Deng. Thomas Gleixner fixed it then
with an explicit check for waiters before calling remove_waiter().
Instead of an explicit NULL check before calling rt_mutex_top_waiter() make
the function return NULL if there are no waiters. With that fixed the now
pointless NULL check is removed from rt_mutex_slowlock().
Reported-and-debugged-by: Yimin Deng <yimin11.deng@gmail.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/CAAh1qt=DCL9aUXNxanP5BKtiPp3m+qj4yB+gDohhXPVFCxWwzg@mail.gmail.com
Link: https://lkml.kernel.org/r/20180327121438.sss7hxg3crqy4ecd@linutronix.de
Diffstat (limited to 'kernel/locking')
| -rw-r--r-- | kernel/locking/rtmutex.c | 3 | ||||
| -rw-r--r-- | kernel/locking/rtmutex_common.h | 11 |
2 files changed, 7 insertions, 7 deletions
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 940633c632541..4f014be7a4b8b 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1268,8 +1268,7 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state, if (unlikely(ret)) { __set_current_state(TASK_RUNNING); - if (rt_mutex_has_waiters(lock)) - remove_waiter(lock, &waiter); + remove_waiter(lock, &waiter); rt_mutex_handle_deadlock(ret, chwalk, &waiter); } diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h index 68686b3ec3c17..d1d62f942be22 100644 --- a/kernel/locking/rtmutex_common.h +++ b/kernel/locking/rtmutex_common.h @@ -52,12 +52,13 @@ static inline int rt_mutex_has_waiters(struct rt_mutex *lock) static inline struct rt_mutex_waiter * rt_mutex_top_waiter(struct rt_mutex *lock) { - struct rt_mutex_waiter *w; - - w = rb_entry(lock->waiters.rb_leftmost, - struct rt_mutex_waiter, tree_entry); - BUG_ON(w->lock != lock); + struct rb_node *leftmost = rb_first_cached(&lock->waiters); + struct rt_mutex_waiter *w = NULL; + if (leftmost) { + w = rb_entry(leftmost, struct rt_mutex_waiter, tree_entry); + BUG_ON(w->lock != lock); + } return w; } |