Subject: Re: [PATCH] per-backing dev unplugging #2
From: Chris Mason <mason@suse.com>
To: Andrew Morton <akpm@osdl.org>
Cc: axboe@suse.de, linux-kernel@vger.kernel.org, kenneth.w.chen@intel.com
In-Reply-To: <20040312120322.0108a437.akpm@osdl.org>
References: <20040311083619.GH6955@suse.de>
	 <1079121113.4181.189.camel@watt.suse.com>
	 <20040312120322.0108a437.akpm@osdl.org>
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Message-Id: <1079121993.4186.204.camel@watt.suse.com>
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Date: Fri, 12 Mar 2004 15:06:34 -0500
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On Fri, 2004-03-12 at 15:03, Andrew Morton wrote:
> Chris Mason <mason@suse.com> wrote:
> >
> > During a mixed load test including fsx-linux and a bunch of procs
> > running cp/read/rm loops, I got a null pointer deref with the call
> > trace:
> > 
> > __lock_page->sync_page->block_sync_page
> > 
> > I don't see how we can trust page->mapping in this path, can't it
> > disappear?  If so, it would be a bug without Jens' patch too, just
> > harder to hit.
> 
> yup.  I wonder why you hit it now.

> This should be sufficient.  All callers of lock_page() should have a ref on
> the inode so ->mapping should be stable even if truncate whips the page off
> the inode.
> 
I thought the same thing, but blk_run_address_space does an if(mapping)
check already.  Looking deeper...

-chris


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