linux-kernel - Re: [PATCH] staging: zcache: fix possible sleep under lock

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Message-ID: <20110822190936.GA12248@shale.localdomain>
Date:	Mon, 22 Aug 2011 22:09:36 +0300
From:	Dan Carpenter <error27@...il.com>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
Cc:	gregkh@...e.de, devel@...verdev.osuosl.org,
	dan.magenheimer@...cle.com, ascardo@...oscopio.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: zcache: fix possible sleep under lock

On Mon, Aug 22, 2011 at 01:47:49PM -0500, Seth Jennings wrote:
> zcache_new_pool() calls kmalloc() with GFP_KERNEL which has
> __GFP_WAIT set.  However, zcache_new_pool() gets called on
> a stack that holds the swap_lock spinlock, leading to a
> possible sleep-with-lock situation. The lock is obtained
> in enable_swap_info().
> 
> The patch replaces GFP_KERNEL with GFP_IOFS, which is
> GFP_KERNEL & ~__GFP_WAIT.
> 

You should use GFP_ATOMIC.  We don't want to do IO with the locks
held.  The only reason GFP_IOFS exists is so that we can turn off
io during suspend and resume.

regards,
dan carpenter

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