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uprobes: Fix the waitqueue_active() check in xol_free_insn_slot()

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The xol_free_insn_slot()->waitqueue_active() check is buggy. We
need mb() after we set the conditon for wait_event(), or
xol_take_insn_slot() can miss the wakeup.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Pratyush Anand <panand@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150721134036.GA4799@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Oleg Nesterov 2015-07-21 15:40:36 +02:00 committed by Ingo Molnar
parent 704bde3cc2
commit 2a742cedcf
1 changed files with 1 additions and 0 deletions
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kernel/events/uprobes.c
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@ -1337,6 +1337,7 @@ static void xol_free_insn_slot(struct task_struct *tsk)
clear_bit(slot_nr, area->bitmap); clear_bit(slot_nr, area->bitmap);
atomic_dec(&area->slot_count); atomic_dec(&area->slot_count);
smp_mb__after_atomic(); /* pairs with prepare_to_wait() */
if (waitqueue_active(&area->wq)) if (waitqueue_active(&area->wq))
wake_up(&area->wq); wake_up(&area->wq);