linux-kernel - Re: vfs related crash in 2.6.33-rc2

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Date:	Wed, 6 Jan 2010 15:41:23 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	Marvin <marvin24@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Trond Myklebust <trond.myklebust@....uio.no>,
	linux-nfs@...r.kernel.org
Subject: Re: vfs related crash in 2.6.33-rc2

On Thu, 31 Dec 2009 05:59:32 +0900
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp> wrote:

> Marvin <marvin24@....de> writes:
> 
> >> Marvin <marvin24@....de> writes:
> >> > Hi,
> >> >
> >> > I'm getting a lot of these:
> >> >
> >> > kernel: general protection fault: 0000 [#1] SMP
> >> > kernel: last sysfs file: /sys/devices/pci0000:00/0000:00:18.3/modalias
> >> > kernel: CPU 0
> >> > kernel: Pid: 12177, comm: packagekitd Not tainted 2.6.33-rc2 #1
> >> > ...
> >> >
> >> > filesystem is ext4 (in case it matters).
> >> 
> >> BTW, are you using nfs client on this machine?
> >>
> >
> > um - yes, now that I think about it... I killed a nfs umount process (because of an 
> > offline server) shortly before the oopses started to fire.
> 
> OK. Probably, this oops would be same with one which happened on my
> machine recently. That path in patch corrupts dcache hash, so it can be
> the cause of strange behavior or oops on dcache hash.
> 
> If so, the attached patch would fix it.
> 
> Thanks.
> -- 
> OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
> 
> 
> Recent change is missing to update "rehash". With that change, it will
> become the cause of adding dentry to hash twice.
> 
> This explains the reason of Oops (dereference the freed dentry in
> __d_lookup()) on my machine.
> 
> Signed-off-by: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
> ---
> 
>  fs/nfs/dir.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff -puN fs/nfs/dir.c~nfs-d_rehash-fix fs/nfs/dir.c
> --- linux-2.6/fs/nfs/dir.c~nfs-d_rehash-fix	2009-12-28 06:18:09.000000000 +0900
> +++ linux-2.6-hirofumi/fs/nfs/dir.c	2009-12-28 06:18:16.000000000 +0900
> @@ -1615,6 +1615,7 @@ static int nfs_rename(struct inode *old_
>  				goto out;
>  
>  			new_dentry = dentry;
> +			rehash = NULL;
>  			new_inode = NULL;
>  		}
>  	}

Guys, what's the status of this fix?  Did Marvin have a chance to test
it?  Are the NFS developers aware of it?

Thanks.

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