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authorPeter Zijlstra <peterz@infradead.org>2018-03-27 14:14:38 +0200
committerThomas Gleixner <tglx@linutronix.de>2018-03-28 23:01:30 +0200
commitc28d62cf52d791ba5f6db7ce525ed06b86291c82 (patch)
tree683f0b9f5b8faa613a46da023b1b7a4bd204c33e /kernel/locking
parentac605bee0bfab40fd5d11964705e907d2d5a32de (diff)
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.c3
-rw-r--r--kernel/locking/rtmutex_common.h11
2 files changed, 7 insertions, 7 deletions
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 940633c63254..4f014be7a4b8 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 68686b3ec3c1..d1d62f942be2 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;
}