linux-kernel - Re: [PATCH RFC] slub: do not drop slab_mutex for sysfs_slab

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Message-ID: <alpine.DEB.2.10.1402061021180.4927@nuc>
Date:	Thu, 6 Feb 2014 10:22:58 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Vladimir Davydov <vdavydov@...allels.com>
cc:	penberg@...nel.org, akpm@...ux-foundation.org, rientjes@...gle.com,
	mhocko@...e.cz, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	devel@...nvz.org
Subject: Re: [PATCH RFC] slub: do not drop slab_mutex for
 sysfs_slab_{add,remove}

On Thu, 6 Feb 2014, Vladimir Davydov wrote:

> When creating/destroying a kmem cache, we do a lot of work holding the
> slab_mutex, but we drop it for sysfs_slab_{add,remove} for some reason.
> Since __kmem_cache_create and __kmem_cache_shutdown are extremely rare,
> I propose to simplify locking by calling sysfs_slab_{add,remove} w/o
> dropping the slab_mutex.

The problem is that sysfs does nasty things like spawning a process in
user space that may lead to something wanting to create slabs too. The
module may then hang waiting on the lock ...

I would be very thankful, if you can get that actually working reliably
without deadlock issues.

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