From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sasha Levin Subject: Re: Hung task when calling clone() due to netfilter/slab Date: Sun, 15 Jan 2012 14:59:44 +0200 Message-ID: <1326632384.11711.3.camel@lappy> References: <1326558605.19951.7.camel@lappy> <1326561043.5287.24.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Dave Jones , davem , Pekka Enberg , Christoph Lameter , Matt Mackall , kaber@trash.net, pablo@netfilter.org, linux-kernel , linux-mm , netfilter-devel@vger.kernel.org, netdev To: Eric Dumazet Return-path: Received: from mail-ee0-f46.google.com ([74.125.83.46]:41706 "EHLO mail-ee0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751152Ab2AOM7w (ORCPT ); Sun, 15 Jan 2012 07:59:52 -0500 In-Reply-To: <1326561043.5287.24.camel@edumazet-laptop> Sender: netfilter-devel-owner@vger.kernel.org List-ID: 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 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 --- 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 -- Sasha.