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
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@ -1268,7 +1268,6 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
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if (unlikely(ret)) {
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__set_current_state(TASK_RUNNING);
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if (rt_mutex_has_waiters(lock))
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remove_waiter(lock, &waiter);
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rt_mutex_handle_deadlock(ret, chwalk, &waiter);
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}
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@ -52,12 +52,13 @@ static inline int rt_mutex_has_waiters(struct rt_mutex *lock)
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static inline struct rt_mutex_waiter *
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rt_mutex_top_waiter(struct rt_mutex *lock)
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{
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struct rt_mutex_waiter *w;
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struct rb_node *leftmost = rb_first_cached(&lock->waiters);
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struct rt_mutex_waiter *w = NULL;
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w = rb_entry(lock->waiters.rb_leftmost,
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struct rt_mutex_waiter, tree_entry);
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if (leftmost) {
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w = rb_entry(leftmost, struct rt_mutex_waiter, tree_entry);
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BUG_ON(w->lock != lock);
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}
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return w;
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}
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