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| author | Peter Zijlstra <peterz@infradead.org> | 2021-09-01 11:44:11 +0200 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2021-09-09 10:31:22 +0200 |
| commit | e5480572706da1b2c2dc2c6484eab64f92b9263b (patch) | |
| tree | 2d686fdbd3bc32ed3aeff1daa4f90150c22169c6 | |
| parent | d66e3edee7af87fe212df611ab9846b987a5070f (diff) | |
| download | linux-e5480572706da1b2c2dc2c6484eab64f92b9263b.tar.bz2 | |
locking/rtmutex: Fix ww_mutex deadlock check
Dan reported that rt_mutex_adjust_prio_chain() can be called with
.orig_waiter == NULL however commit a055fcc132d4 ("locking/rtmutex: Return
success on deadlock for ww_mutex waiters") unconditionally dereferences it.
Since both call-sites that have .orig_waiter == NULL don't care for the
return value, simply disable the deadlock squash by adding the NULL check.
Notably, both callers use the deadlock condition as a termination condition
for the iteration; once detected, it is sure that (de)boosting is done.
Arguably step [3] would be a more natural termination point, but it's
dubious whether adding a third deadlock detection state would improve the
code.
Fixes: a055fcc132d4 ("locking/rtmutex: Return success on deadlock for ww_mutex waiters")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/YS9La56fHMiCCo75@hirez.programming.kicks-ass.net
| -rw-r--r-- | kernel/locking/rtmutex.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 8eabdc79602b..6bb116c559b4 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -753,7 +753,7 @@ static int __sched rt_mutex_adjust_prio_chain(struct task_struct *task, * other configuration and we fail to report; also, see * lockdep. */ - if (IS_ENABLED(CONFIG_PREEMPT_RT) && orig_waiter->ww_ctx) + if (IS_ENABLED(CONFIG_PREEMPT_RT) && orig_waiter && orig_waiter->ww_ctx) ret = 0; raw_spin_unlock(&lock->wait_lock); |