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Date: Mon, 3 Mar 1997 23:50:57 -0600
From: Jonathan Lemon <jlemon@americantv.com>
To: Michael Smith <msmith@atrad.adelaide.edu.au>
Cc: proff@iq.org, hackers@FreeBSD.ORG
Subject: Re: xemacs crashes kernel
References: <19970303230157.25741@right.PCS> <199703040532.QAA10831@genesis.atrad.adelaide.edu.au>
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In-Reply-To: <199703040532.QAA10831@genesis.atrad.adelaide.edu.au>; from Michael Smith on Mar 03, 1997 at 04:02:00PM +1030
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On Mar 03, 1997 at 04:02:00PM +1030, Michael Smith wrote:
>         error = VOP_FSYNC(vp, fp->f_cred,
>                 (vp->v_mount->mnt_flag & MNT_ASYNC) ? MNT_NOWAIT : MNT_WAIT, p);
> 
> MNT_ASYNC is 0x40, and mnt_flag looks to be about 0x18 offset in the
> mount structure.  Looks like maybe someone trying to fsync something
> that's not a file, although a quick test here doesn't indicate that.
> 
> Are non-file items supposed to have valid v_mount pointers?  Other places
> in the kernel that look at vp->v_mount often check it against zero first;
> should that be done here, eg.
> 
> 	(vp->v_mount && (vp->v_mount->mnt_flag & MNT_ASYNC)) ? MNT_NOWAIT...
> 
> as well?  This looks like it might have been overlooked when the async
> filesystem stuff came in, as old versions of this code read :
> 
>         error = VOP_FSYNC(vp, fp->f_cred, MNT_WAIT, p);
> 
> Suggestions?  Jonathan, can you try the above and see if it cures your
> problem?

I changed the fsync code to read:

        error = VOP_FSYNC(vp, fp->f_cred,
                (vp->v_mount && (vp->v_mount->mnt_flag & MNT_ASYNC)) ? 
                MNT_NOWAIT : MNT_WAIT, p);

And it doesn't crash the kernel any more.  I'm not sure if this is 
the right fix or not.  Julian - you might want to try this as well.
(btw, mail to @iq.com bounces from here.  :-( )
--
Jonathan