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authorPeter Zijlstra <peterz@infradead.org>2021-09-01 12:44:11 +0300
committerThomas Gleixner <tglx@linutronix.de>2021-09-09 11:31:22 +0300
commite5480572706da1b2c2dc2c6484eab64f92b9263b (patch)
tree2d686fdbd3bc32ed3aeff1daa4f90150c22169c6 /kernel/locking
parentd66e3edee7af87fe212df611ab9846b987a5070f (diff)
downloadlinux-e5480572706da1b2c2dc2c6484eab64f92b9263b.tar.xz
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
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/rtmutex.c2
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);