From: Eric Dumazet <eric.dumazet@gmail.com>
To: Sasha Levin <levinsasha928@gmail.com>
Cc: Dave Jones <davej@redhat.com>, davem <davem@davemloft.net>,
Pekka Enberg <penberg@kernel.org>,
Christoph Lameter <cl@linux-foundation.org>,
Matt Mackall <mpm@selenic.com>,
kaber@trash.net, pablo@netfilter.org,
linux-kernel <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
netfilter-devel@vger.kernel.org, netdev <netdev@vger.kernel.org>
Subject: Re: Hung task when calling clone() due to netfilter/slab
Date: Sun, 15 Jan 2012 18:25:05 +0100 [thread overview]
Message-ID: <1326648305.5287.78.camel@edumazet-laptop> (raw)
In-Reply-To: <1326632384.11711.3.camel@lappy>
Le dimanche 15 janvier 2012 à 14:59 +0200, Sasha Levin a écrit :
> On Sat, 2012-01-14 at 18:10 +0100, Eric Dumazet wrote:
> > Apparently SLUB calls sysfs_slab_add() from kmem_cache_create() while
> > still holding slub_lock.
> >
> > So if the task launched needs to "cat /proc/slabinfo" or anything
> > needing slub_lock, its a deadlock.
>
> I've made the following patch to test it, It doesn't look like it's
> the correct solution, but it verifies that the problem is there (it
> works well with the patch).
>
> ---------------
>
> From cc4874b491b8e5d9d1ea5bf2032413efdbddced8 Mon Sep 17 00:00:00 2001
> From: Sasha Levin <levinsasha928@gmail.com>
> Date: Sun, 15 Jan 2012 14:55:03 +0200
> Subject: [PATCH] slab: Fix hang when creating sysfs entries
>
> This patch fixes the hang which happens when we create a sysfs entry and call
> back to userspace. If the usermode helper tries to do anything which involves
> slub_lock we will hang since slub_lock is already held.
>
> Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
> ---
> mm/slub.c | 2 ++
> 1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 4907563..6948327 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5283,7 +5283,9 @@ static int sysfs_slab_add(struct kmem_cache *s)
> kobject_put(&s->kobj);
> return err;
> }
> + up_write(&slub_lock);
> kobject_uevent(&s->kobj, KOBJ_ADD);
> + down_write(&slub_lock);
> if (!unmergeable) {
> /* Setup first alias */
> sysfs_slab_alias(s, s->name);
> --
> 1.7.8.3
>
>
Oh well, that cannot be right. Dont send official patches if you already
know "it's not the correct solution", we already know where is the
problem.
It's _never_ right to release a lock for a short time without any
additional checks. [ If it was right, the lock would be not needed ]
As soon as the slub_lock is released, another thread can come and find
the new kmem_cache.
For example, it can destroy it, and your thread is going to access s
while it was already freed.
sysfs_slab_alias(s, s->name); // crash
next prev parent reply other threads:[~2012-01-15 17:25 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-14 16:30 Hung task when calling clone() due to netfilter/slab Sasha Levin
2012-01-14 17:10 ` Eric Dumazet
2012-01-14 17:18 ` Eric Dumazet
2012-01-15 12:59 ` Sasha Levin
2012-01-15 17:25 ` Eric Dumazet [this message]
2012-01-17 15:12 ` Christoph Lameter
2012-01-17 15:20 ` Eric Dumazet
2012-01-17 15:27 ` Christoph Lameter
2012-01-17 15:30 ` Eric Dumazet
2012-01-17 16:04 ` Christoph Lameter
2012-01-17 22:22 ` Christoph Lameter
2012-01-19 21:43 ` Eric W. Biederman
2012-01-19 22:15 ` Eric W. Biederman
2012-01-20 2:03 ` Christoph Lameter
2012-01-20 2:31 ` Eric W. Biederman
2012-01-20 14:49 ` Christoph Lameter
2012-01-20 20:40 ` Eric W. Biederman
2012-02-01 8:05 ` Pekka Enberg
2012-02-01 17:32 ` Eric W. Biederman
2012-02-01 8:07 ` Pekka Enberg
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=1326648305.5287.78.camel@edumazet-laptop \
--to=eric.dumazet@gmail.com \
--cc=cl@linux-foundation.org \
--cc=davej@redhat.com \
--cc=davem@davemloft.net \
--cc=kaber@trash.net \
--cc=levinsasha928@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mpm@selenic.com \
--cc=netdev@vger.kernel.org \
--cc=netfilter-devel@vger.kernel.org \
--cc=pablo@netfilter.org \
--cc=penberg@kernel.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).