From: Johannes Weiner <hannes@cmpxchg.org>
To: Michal Hocko <mhocko@suse.com>
Cc: Alan Cox <alan@llwyncelyn.cymru>, Christoph Hellwig <hch@lst.de>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com
Subject: tty crash due to auto-failing vmalloc
Date: Tue, 3 Oct 2017 18:55:04 -0400 [thread overview]
Message-ID: <20171003225504.GA966@cmpxchg.org> (raw)
On some of our machines, we see this warning:
/* switch the line discipline */
tty->ldisc = ld;
tty_set_termios_ldisc(tty, disc);
retval = tty_ldisc_open(tty, tty->ldisc);
if (retval) {
-> if (!WARN_ON(disc == N_TTY)) {
tty_ldisc_put(tty->ldisc);
tty->ldisc = NULL;
}
}
where the stack is
tty_ldisc_reinit
tty_ldisc_hangup
__tty_hangup
do_exit
do_signal
syscall
This is followed by a NULL pointer deref crash in n_tty_set_termios,
presumably when it tries to deref that unallocated tty->disc_data.
The only way n_tty_open() can fail is if the vmalloc in there fails.
struct n_tty_data isn't terribly big, but ever since the following
patch it doesn't even *try* the allocation:
commit 5d17a73a2ebeb8d1c6924b91e53ab2650fe86ffb
Author: Michal Hocko <mhocko@suse.com>
Date: Fri Feb 24 14:58:53 2017 -0800
vmalloc: back off when the current task is killed
__vmalloc_area_node() allocates pages to cover the requested vmalloc
size. This can be a lot of memory. If the current task is killed by
the OOM killer, and thus has an unlimited access to memory reserves, it
can consume all the memory theoretically. Fix this by checking for
fatal_signal_pending and back off early.
Link: http://lkml.kernel.org/r/20170201092706.9966-4-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This talks about the oom killer and memory exhaustion, but most fatal
signals don't happen due to the OOM killer.
I think this patch should be reverted. If somebody is vmallocing crazy
amounts of memory in the exit path we should probably track them down
individually; the patch doesn't reference any real instances of that.
But we cannot start failing allocations that have never failed before.
That said, maybe we want Alan's N_NULL failover in the hangup path too?
next reply other threads:[~2017-10-03 22:55 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-03 22:55 Johannes Weiner [this message]
2017-10-03 23:51 ` tty crash due to auto-failing vmalloc 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
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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