From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qa0-f53.google.com (mail-qa0-f53.google.com [209.85.216.53]) by kanga.kvack.org (Postfix) with ESMTP id 7DB0E6B0036 for ; Thu, 6 Feb 2014 18:02:10 -0500 (EST) Received: by mail-qa0-f53.google.com with SMTP id cm18so3922254qab.26 for ; Thu, 06 Feb 2014 15:02:10 -0800 (PST) Received: from qmta13.emeryville.ca.mail.comcast.net (qmta13.emeryville.ca.mail.comcast.net. [2001:558:fe2d:44:76:96:27:243]) by mx.google.com with ESMTP id p9si611693qcr.35.2014.02.06.11.13.24 for ; Thu, 06 Feb 2014 11:13:54 -0800 (PST) Date: Thu, 6 Feb 2014 13:13:20 -0600 (CST) From: Christoph Lameter Subject: Re: [PATCH RFC] slub: do not drop slab_mutex for sysfs_slab_{add,remove} In-Reply-To: <52F3CF12.70905@parallels.com> Message-ID: References: <1391702294-27289-1-git-send-email-vdavydov@parallels.com> <52F3CF12.70905@parallels.com> Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Vladimir Davydov Cc: penberg@kernel.org, akpm@linux-foundation.org, rientjes@google.com, mhocko@suse.cz, linux-kernel@vger.kernel.org, linux-mm@kvack.org, devel@openvz.org On Thu, 6 Feb 2014, Vladimir Davydov wrote: > Hmm... IIUC the only function of concern is kobject_uevent() - > everything else called from sysfs_slab_{add,remove} is a mix of kmalloc, > kfree, mutex_lock/unlock - in short, nothing dangerous. There we do > call_usermodehelper(), but we do it with UMH_WAIT_EXEC, which means > "wait for exec only, but not for the process to complete". An exec > shouldn't issue any slab-related stuff AFAIU. At least, I tried to run > the patched kernel with lockdep enabled and got no warnings at all when > getting uevents about adding/removing caches. That's why I started to > doubt whether we really need this lock... > > Please correct me if I'm wrong. I have had this deadlock a couple of years ago. Sysfs seems to change over time. Not sure if that is still the case. > > I would be very thankful, if you can get that actually working reliably > > without deadlock issues. > > If there is no choice rather than moving sysfs_slab_{add,remove} out of > the slab_mutex critical section, I'll have to do it that way. But first > I'd like to make sure it cannot be done with less footprint. I am all for holding the lock as long as possible. -- 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: email@kvack.org