From: Oleg Nesterov <oleg@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nick Piggin <npiggin@gmail.com>,
Peter Zijlstra <peterz@infradead.org>,
Mel Gorman <mgorman@techsingularity.net>, Jan Kara <jack@suse.cz>,
Davidlohr Bueso <dave@stgolabs.net>,
Andi Kleen <ak@linux.intel.com>,
Lukas Czerner <lczerner@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: wait_on_page_bit_common(TASK_KILLABLE, EXCLUSIVE) can miss wakeup?
Date: Wed, 24 Jun 2020 18:43:20 +0200 [thread overview]
Message-ID: <20200624164319.GA12203@redhat.com> (raw)
In-Reply-To: <CAHk-=wjqnKdrjZx0kO+f1vyFQFcb-HZsbHFw6_jAeuQmNsTsbQ@mail.gmail.com>
On 06/24, Linus Torvalds wrote:
>
> That said, I'm not entirely happy with your patch.
Neither me,
> The real problem, I feel, is that
>
> if (likely(bit_is_set))
> io_schedule();
>
> anti-pattern. Without that, we wouldn't have the bug.
>
> Normally, we'd be TASK_RUNNING in this sequence, but because we might
> skip io_schedule(), we can still be in a "sleeping" state here and be
> "woken up" between that bit setting and the signal check.
Ah.
And now it _seems_ to me that even if io_schedule() is called
try_to_wake_up() can "falsely" succed if signal_pending_state() is true,
even if __schedule() won't block in this case.
But I am sure I missed something else. I spent to much time reading the
random code paths today, I'll return tomorrow.
Oleg.
prev parent reply other threads:[~2020-06-24 16:43 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-24 16:11 wait_on_page_bit_common(TASK_KILLABLE, EXCLUSIVE) can miss wakeup? Oleg Nesterov
2020-06-24 16:20 ` Oleg Nesterov
2020-06-24 16:36 ` Linus Torvalds
2020-06-26 15:43 ` Peter Zijlstra
2020-06-28 5:39 ` Linus Torvalds
2020-06-28 13:18 ` Peter Zijlstra
2020-06-29 3:28 ` Nicholas Piggin
2020-06-29 13:16 ` Nicholas Piggin
2020-06-29 16:36 ` Linus Torvalds
2020-06-30 2:12 ` Nicholas Piggin
2020-06-29 14:02 ` Oleg Nesterov
2020-06-30 2:08 ` Nicholas Piggin
2020-06-30 6:17 ` Oleg Nesterov
2020-06-30 9:08 ` Nicholas Piggin
2020-06-30 10:53 ` Oleg Nesterov
2020-06-30 11:36 ` Oleg Nesterov
2020-06-30 11:50 ` Oleg Nesterov
2020-06-30 18:02 ` Linus Torvalds
2020-06-30 18:29 ` Oleg Nesterov
2020-06-30 18:57 ` Linus Torvalds
2020-06-29 15:13 ` Oleg Nesterov
2020-06-24 16:22 ` Linus Torvalds
2020-06-24 16:43 ` Oleg Nesterov [this message]
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