linux-kernel - Re: [PATCH 1/2] Revert "vmalloc: back off when the current task is killed"

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Date:   Wed, 4 Oct 2017 17:00:27 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alan Cox <alan@...yncelyn.cymru>,
        Christoph Hellwig <hch@....de>, Michal Hocko <mhocko@...e.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 1/2] Revert "vmalloc: back off when the current task is
 killed"

On Thu, Oct 05, 2017 at 05:49:43AM +0900, Tetsuo Handa wrote:
> On 2017/10/05 3:59, Johannes Weiner wrote:
> > But the justification to make that vmalloc() call fail like this isn't
> > convincing, either. The patch mentions an OOM victim exhausting the
> > memory reserves and thus deadlocking the machine. But the OOM killer
> > is only one, improbable source of fatal signals. It doesn't make sense
> > to fail allocations preemptively with plenty of memory in most cases.
> 
> By the time the current thread reaches do_exit(), fatal_signal_pending(current)
> should become false. As far as I can guess, the source of fatal signal will be
> tty_signal_session_leader(tty, exit_session) which is called just before
> tty_ldisc_hangup(tty, cons_filp != NULL) rather than the OOM killer. I don't
> know whether it is possible to make fatal_signal_pending(current) true inside
> do_exit() though...

It's definitely not the OOM killer, the memory situation looks fine
when this happens. I didn't look closer where the signal comes from.

That said, we trigger this issue fairly easily. We tested the revert
over night on a couple thousand machines, and it fixed the issue
(whereas the control group still saw the crashes).