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

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Message-ID: <20080605063253.40787ca3@tleilax.poochiereds.net>
Date:	Thu, 5 Jun 2008 06:32:53 -0400
From:	Jeff Layton <jlayton@...hat.com>
To:	"Daniel J Blueman" <daniel.blueman@...il.com>
Cc:	chucklever@...il.com, 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, 5 Jun 2008 09:28:51 +0100
"Daniel J Blueman" <daniel.blueman@...il.com> wrote:

> 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

Yeah, after I sent that I went back and looked and it seemed like
while we don't hold the BKL there, access to the callback info is still
serialized via a semaphore. Thanks for testing it anyway...

-- 
Jeff Layton <jlayton@...hat.com>
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