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authorPrateek Sood <prsood@codeaurora.org>2018-11-30 20:40:56 +0530
committerIngo Molnar <mingo@kernel.org>2019-01-21 11:15:36 +0100
commit6dc080eeb2ba01973bfff0d79844d7a59e12542e (patch)
tree9deefb59370b698572b87e0c3467c87cd3a3f9bc
parentd7393226d15add056285c8fc86723d54d7e0c77d (diff)
downloadlinux-6dc080eeb2ba01973bfff0d79844d7a59e12542e.tar.bz2
sched/wait: Fix rcuwait_wake_up() ordering
For some peculiar reason rcuwait_wake_up() has the right barrier in the comment, but not in the code. This mistake has been observed to cause a deadlock in the following situation: P1 P2 percpu_up_read() percpu_down_write() rcu_sync_is_idle() // false rcu_sync_enter() ... __percpu_up_read() [S] ,- __this_cpu_dec(*sem->read_count) | smp_rmb(); [L] | task = rcu_dereference(w->task) // NULL | | [S] w->task = current | smp_mb(); | [L] readers_active_check() // fail `-> <store happens here> Where the smp_rmb() (obviously) fails to constrain the store. [ peterz: Added changelog. ] Signed-off-by: Prateek Sood <prsood@codeaurora.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Andrea Parri <andrea.parri@amarulasolutions.com> Acked-by: Davidlohr Bueso <dbueso@suse.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Fixes: 8f95c90ceb54 ("sched/wait, RCU: Introduce rcuwait machinery") Link: https://lkml.kernel.org/r/1543590656-7157-1-git-send-email-prsood@codeaurora.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--kernel/exit.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index 284f2fe9a293..3fb7be001964 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -307,7 +307,7 @@ void rcuwait_wake_up(struct rcuwait *w)
* MB (A) MB (B)
* [L] cond [L] tsk
*/
- smp_rmb(); /* (B) */
+ smp_mb(); /* (B) */
/*
* Avoid using task_rcu_dereference() magic as long as we are careful,