linux-kernel - Re: [2.6.26-rc4] mount.nfsv4/memory poisoning issues...

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Date:	Thu, 5 Jun 2008 09:28:51 +0100
From:	"Daniel J Blueman" <daniel.blueman@...il.com>
To:	"Jeff Layton" <jlayton@...hat.com>, chucklever@...il.com
Cc:	linux-nfs@...r.kernel.org, nfsv4@...ux-nfs.org,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [2.6.26-rc4] mount.nfsv4/memory poisoning issues...

On Thu, Jun 5, 2008 at 1:35 AM, Jeff Layton <jlayton@...hat.com> wrote:
> On Thu, 5 Jun 2008 00:33:54 +0100
> "Daniel J Blueman" <daniel.blueman@...il.com> wrote:
>
>> Having experienced 'mount.nfs4: internal error' when mounting nfsv4 in
>> the past, I have a minimal test-case I sometimes run:
>>
>> $ while :; do mount -t nfs4 filer:/store /store; umount /store; done
>>
>> After ~100 iterations, I saw the 'mount.nfs4: internal error',
>> followed by symptoms of memory corruption [1], a locking issue with
>> the reporting [2] and another (related?) memory-corruption issue
>> (off-by-1?) [3]. A little analysis shows memory being overwritten by
>> (likely) a poison value, which gets complicated if it's not
>> use-after-free...
>>
>> Anyone dare confirm this issue? NFSv4 server is x86-64 Ubuntu 8.04
>> 2.6.24-18, client U8.04 2.6.26-rc4; batteries included [4].
>>
>> I'm happy to decode addresses, test patches etc.
>>
>> Daniel
>>
>
> Looks like it fell down while trying to take down the kthread during a
> failed mount attempt. I have to wonder if I might have introduced a
> race when I changed nfs4 callback thread to kthread API. I think we may
> need the BKL around the last 2 statements in the main callback thread
> function. If you can easily reproduce this, could you test the
> following patch and let me know if it helps?
>
> Note that this patch is entirely untested, so test it someplace
> non-critical ;-).
>
> Signed-off-by: Jeff Layton <jlayton@...hat.com>
>
>
> diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
> index c1e7c83..a3e83f9 100644
> --- a/fs/nfs/callback.c
> +++ b/fs/nfs/callback.c
> @@ -90,9 +90,9 @@ nfs_callback_svc(void *vrqstp)
>                preverr = err;
>                svc_process(rqstp);
>        }
> -       unlock_kernel();
>        nfs_callback_info.task = NULL;
>        svc_exit_thread(rqstp);
> +       unlock_kernel();
>        return 0;
>  }

This doesn't resolve the issue, alas. I'll hunker down to the
bisection in the next few days.

Thanks,
  Daniel
-- 
Daniel J Blueman
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