From: Michal Hocko <mhocko@kernel.org>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Alan Cox <alan@llwyncelyn.cymru>, Christoph Hellwig <hch@lst.de>,
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: Thu, 5 Oct 2017 09:54:43 +0200 [thread overview]
Message-ID: <20171005075443.hxv2msxulh6pepf3@dhcp22.suse.cz> (raw)
In-Reply-To: <20171004185906.GB2136@cmpxchg.org>
On Wed 04-10-17 14:59:06, Johannes Weiner 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.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
> ---
> mm/vmalloc.c | 6 ------
> 1 file changed, 6 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 8a43db6284eb..673942094328 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1695,11 +1695,6 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
> for (i = 0; i < area->nr_pages; i++) {
> struct page *page;
>
> - if (fatal_signal_pending(current)) {
> - area->nr_pages = i;
> - goto fail_no_warn;
> - }
> -
> if (node == NUMA_NO_NODE)
> page = alloc_page(alloc_mask|highmem_mask);
> else
> @@ -1723,7 +1718,6 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
> warn_alloc(gfp_mask, NULL,
> "vmalloc: allocation failure, allocated %ld of %ld bytes",
> (area->nr_pages*PAGE_SIZE), area->size);
> -fail_no_warn:
> vfree(area->addr);
> return NULL;
> }
> --
> 2.14.1
--
Michal Hocko
SUSE Labs
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-10-05 9:03 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
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 [this message]
2017-10-04 18:59 ` [PATCH 2/2] tty: fall back to N_NULL if switching to N_TTY fails during hangup Johannes Weiner
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20171005075443.hxv2msxulh6pepf3@dhcp22.suse.cz \
--to=mhocko@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=alan@llwyncelyn.cymru \
--cc=hannes@cmpxchg.org \
--cc=hch@lst.de \
--cc=kernel-team@fb.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).