From: Andrew Morton <akpm@linux-foundation.org>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Alan Cox <alan@llwyncelyn.cymru>, Christoph Hellwig <hch@lst.de>,
Michal Hocko <mhocko@suse.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com
Subject: Re: [PATCH 1/2] Revert "vmalloc: back off when the current task is killed"
Date: Wed, 4 Oct 2017 15:32:45 -0700 [thread overview]
Message-ID: <20171004153245.2b08d831688bb8c66ef64708@linux-foundation.org> (raw)
In-Reply-To: <20171004185906.GB2136@cmpxchg.org>
On Wed, 4 Oct 2017 14:59:06 -0400 Johannes Weiner <hannes@cmpxchg.org> wrote:
> This reverts commit 5d17a73a2ebeb8d1c6924b91e53ab2650fe86ffb and
> commit 171012f561274784160f666f8398af8b42216e1f.
>
> 5d17a73a2ebe ("vmalloc: back off when the current task is killed")
> made all vmalloc allocations from a signal-killed task fail. We have
> seen crashes in the tty driver from this, where a killed task exiting
> tries to switch back to N_TTY, fails n_tty_open because of the vmalloc
> failing, and later crashes when dereferencing tty->disc_data.
>
> Arguably, relying on a vmalloc() call to succeed in order to properly
> exit a task is not the most robust way of doing things. There will be
> a follow-up patch to the tty code to fall back to the N_NULL ldisc.
>
> 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.
>
> The patch doesn't mention real-life instances where vmalloc sites
> would exhaust memory, which makes it sound more like a theoretical
> issue to begin with. But just in case, the OOM access to memory
> reserves has been restricted on the allocator side in cd04ae1e2dc8
> ("mm, oom: do not rely on TIF_MEMDIE for memory reserves access"),
> which should take care of any theoretical concerns on that front.
>
> Revert this patch, and the follow-up that suppresses the allocation
> warnings when we fail the allocations due to a signal.
You don't think they should be backported into -stables?
next prev parent reply other threads:[~2017-10-04 22:32 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-03 22:55 tty crash due to auto-failing vmalloc Johannes Weiner
2017-10-03 23:51 ` Alan Cox
2017-10-04 8:33 ` Michal Hocko
2017-10-04 18:58 ` Johannes Weiner
2017-10-04 18:59 ` [PATCH 1/2] Revert "vmalloc: back off when the current task is killed" Johannes Weiner
2017-10-04 20:49 ` Tetsuo Handa
2017-10-04 21:00 ` Johannes Weiner
2017-10-04 21:42 ` Tetsuo Handa
2017-10-04 23:21 ` Johannes Weiner
2017-10-04 22:32 ` Andrew Morton [this message]
2017-10-04 23:18 ` Johannes Weiner
2017-10-05 7:57 ` Michal Hocko
2017-10-05 10:36 ` Tetsuo Handa
2017-10-05 10:49 ` Michal Hocko
2017-10-07 2:21 ` Tetsuo Handa
2017-10-07 2:51 ` Johannes Weiner
2017-10-07 4:05 ` Tetsuo Handa
2017-10-07 7:59 ` Michal Hocko
2017-10-07 9:57 ` Tetsuo Handa
2017-10-05 6:49 ` Vlastimil Babka
2017-10-05 7:54 ` Michal Hocko
2017-10-04 18:59 ` [PATCH 2/2] tty: fall back to N_NULL if switching to N_TTY fails during hangup Johannes Weiner
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