From owner-freebsd-current  Tue Jan  4 10:38:48 2000
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Date: Tue, 4 Jan 2000 10:38:45 -0800 (PST)
From: Matthew Dillon <dillon@apollo.backplane.com>
Message-Id: <200001041838.KAA37128@apollo.backplane.com>
To: freebsd-current@FreeBSD.ORG
Subject: Re: NFS Race
References: <20000104123804.23965@ns.int.ftf.net> <200001041655.IAA23681@apollo.backplane.com> <20000104120247.A49618@snickers.org> <387233BE.9733079A@dead-end.net>
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:Me too ;)
:
:I got almost 300 of these messages during a "make release" with the
:chroot dir NFS mounted. Otherwise I had no problems with such over
:NFS created files though.
:
:Daniel

    I think I've tracked it down.  When the client close()'s an NFS filehandle
    it calls nfs_flush() without specifying that a commit should be done, then
    clears the NMODIFIED bit in np->n_flags.  It is not legal to clear
    NMODIFIED if no commit is done.

    Clearing NMODIFIED prematurely causes NFS to believe that there are no
    dirty buffers to destroy when a new file is created with O_TRUNC or
    ftruncate().  This will not lead to any problems if all you are doing is 
    appending, it will lead to problems if you seek/write around after 
    truncating the file.

    I think the correct solution is simply to not clear NMODIFIED on the
    last close.

    Please try this patch to -current

					-Matt
					Matthew Dillon 
					<dillon@backplane.com>

Index: nfs_vnops.c
===================================================================
RCS file: /FreeBSD/FreeBSD-CVS/src/sys/nfs/nfs_vnops.c,v
retrieving revision 1.149
diff -u -r1.149 nfs_vnops.c
--- nfs_vnops.c	1999/12/15 23:02:19	1.149
+++ nfs_vnops.c	2000/01/04 18:26:50
@@ -561,10 +561,15 @@
 	    if ((VFSTONFS(vp->v_mount)->nm_flag & NFSMNT_NQNFS) == 0 &&
 		(np->n_flag & NMODIFIED)) {
 		if (NFS_ISV3(vp)) {
+		    /*
+		     * Note: Since we haven't committed the buffers we cannot
+		     * clear the NMODIFIED np->n_flag
+		     */
 		    error = nfs_flush(vp, ap->a_cred, MNT_WAIT, ap->a_p, 0);
-		    np->n_flag &= ~NMODIFIED;
-		} else
+		    /* np->n_flag &= ~NMODIFIED; */
+		} else {
 		    error = nfs_vinvalbuf(vp, V_SAVE, ap->a_cred, ap->a_p, 1);
+		}
 		np->n_attrstamp = 0;
 	    }
 	    if (np->n_flag & NWRITEERR) {


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