On Wed, 2011-01-12 at 11:10 -0500, Nick Bowler wrote:
> With 2.6.37 (client), opens on NFS with O_CREAT | O_EXCL are
> occasionally succeeding when the file already exists, apparently
> depending on the state of the filesystem cache. The issue was observed
> because mplayer would randomly overwrite its config file...
>
> Using the test program (./nfsbreak) included in this mail, I can
> reproduce it as follows (/home/nbowler is the NFS mount point). No
> interesting kernel messages appear on either the client or server
> machines during the test:
>
> % mkdir /home/nbowler/nfsexcl
> % ./nfsbreak
> nfsbreak: File opened <<< This is OK
> % ./nfsbreak
> nfsbreak: File exists
> % ./nfsbreak
> nfsbreak: File exists
> % su -c 'echo 2 > /proc/sys/vm/drop_caches'
> % ./nfsbreak
> nfsbreak: File opened <<< Uhoh!
> % ./nfsbreak
> nfsbreak: File exists
>
> Here's the nfsbreak C source:
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <fcntl.h>
>
> int main(void)
> {
> int fd;
>
> /* /home/nbowler is the NFS mount point */
> fd = open("/home/nbowler/nfsexcl/nfsexcl", O_WRONLY|O_CREAT|O_EXCL);
> if (fd == -1) {
> perror("nfsbreak");
> return EXIT_FAILURE;
> }
>
> puts("nfsbreak: File opened");
> return 0;
> }
>
> This is a regression from 2.6.36; bisection implicates the following,
> which unfortunately does not revert cleanly.
Confirmed. The breakage does not affect NFSv4, but is limited to NFSv3.
The following patch should therefore suffice to fix it.
Cheers
Trond
8<---------------------------------------------------------------------
>From 1ec00b0d759586211447fec763f6c633759e4b3e Mon Sep 17 00:00:00 2001
From: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
Date: Wed, 12 Jan 2011 13:19:59 -0500
Subject: [PATCH] NFS: Fix NFSv3 exclusive open semantics
Commit c0204fd2b8fe047b18b67e07e1bf2a03691240cd (NFS: Clean up
nfs4_proc_create()) broke NFSv3 exclusive open by removing the code
that passes the O_EXCL flag down to nfs3_proc_create(). This patch
reverts that offending hunk from the original commit.
Reported-by: Nick Bowler <nbowler@xxxxxxxxxxxxxxxx>
Signed-off-by: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
Cc: stable@xxxxxxxxxx [2.6.37]
---
fs/nfs/dir.c | 6 +++++-
1 files changed, 5 insertions(+), 1 deletions(-)
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index abe4f0c..f9d6a37 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1583,6 +1583,7 @@ static int nfs_create(struct inode *dir, struct dentry *dentry, int mode,
{
struct iattr attr;
int error;
+ int open_flags = 0;
dfprintk(VFS, "NFS: create(%s/%ld), %s\n",
dir->i_sb->s_id, dir->i_ino, dentry->d_name.name);
@@ -1590,7 +1591,10 @@ static int nfs_create(struct inode *dir, struct dentry *dentry, int mode,
attr.ia_mode = mode;
attr.ia_valid = ATTR_MODE;
- error = NFS_PROTO(dir)->create(dir, dentry, &attr, 0, NULL);
+ if ((nd->flags & LOOKUP_CREATE) != 0)
+ open_flags = nd->intent.open.flags;
+
+ error = NFS_PROTO(dir)->create(dir, dentry, &attr, open_flags, NULL);
if (error != 0)
goto out_err;
return 0;
--
1.7.3.4
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
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