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Date: Sat, 27 Apr 2002 04:52:13 -0700 (PDT)
From: Robert Morris <rtm@lcs.mit.edu>
To: freebsd-gnats-submit@FreeBSD.org
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Subject: kern/37502: NFS client ignores mtime.tv_usec for open/close cache consistency
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>Number:         37502
>Category:       kern
>Synopsis:       NFS client ignores mtime.tv_usec for open/close cache consistency
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sat Apr 27 05:00:02 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Robert Morris
>Release:        4.5
>Organization:
MIT/LCS
>Environment:
FreeBSD nephron.lcs.mit.edu 4.5-RELEASE FreeBSD 4.5-RELEASE #3: Thu Apr 11 11:59:46 EDT 2002     rtm@nephron.lcs.mit.edu:/usr/src/sys/compile/PDOS-X23  i386
>Description:
When you open a file, the NFS client code doesn't always
correctly notice whether the file has been changed on the
server, and thus doesn't always correctly ignore stale
cached blocks for that file. The NFS client code looks to
see if the file's mtime has changed, but only checks the
seconds, not the microseconds. So reading a file that changes twice
in rapid succession may yield stale data.
>How-To-Repeat:
Two clients, X and Y, mount the same NFS file system. Do this
sequence all within the same second of time:

X% echo 111 > foo
Y% cat foo
X% echo 222 > foo
Y% cat foo

The correct answer is 222, but you will sometimes get 111.

>Fix:
The following code from nfs_bio.c should check whether the
mtime microseconds (and perhaps file length) have changed,
as well as checking the seconds:

      		error = VOP_GETATTR(vp, &vattr, cred, td);
		if (error)
			return (error);
		if (np->n_mtime != vattr.va_mtime.tv_sec) {
			if (vp->v_type == VDIR)
				nfs_invaldir(vp);
			error = nfs_vinvalbuf(vp, V_SAVE, cred, td, 1);

>Release-Note:
>Audit-Trail:
>Unformatted:

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