linux-kernel - Re: wait_on_page_bit_common(TASK_KILLABLE, EXCLUSIVE) can miss wakeup?

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Message-ID: <20200624162042.GA12238@redhat.com>
Date:   Wed, 24 Jun 2020 18:20:42 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Nick Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Jan Kara <jack@...e.cz>, Davidlohr Bueso <dave@...olabs.net>,
        Andi Kleen <ak@...ux.intel.com>
Cc:     Lukas Czerner <lczerner@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: wait_on_page_bit_common(TASK_KILLABLE, EXCLUSIVE) can miss
 wakeup?

On 06/24, Oleg Nesterov wrote:
> Suppose that 2 threads T1 and T2 call __lock_page_killable() and sleep in
> wait_on_page_bit_common() -> io_schedule().
>
> T1 is killed, it does test_and_set_bit_lock() but the page is still locked.
>
> unlock_page() calls __wake_up_common(nr_exclusive = 1), this wakes T1 up.
> T2 is not woken.

Ah, please ignore me, sorry for noise.

If T1 is killed it is TASK_RUNNING, try_to_wake_up() should return 0.

Oleg.