[PATCH 3.16 130/328] fs/9p/xattr.c: catch the error of p9_client_clunk when setting xattr failed

[Ben Hutchings]

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: piaojun <piaojun@xxxxxxxxxx>

commit 3111784bee81591ea2815011688d28b65df03627 upstream.

In my testing, v9fs_fid_xattr_set will return successfully even if the
backend ext4 filesystem has no space to store xattr key-value. That will
cause inconsistent behavior between front end and back end. The reason is
that lsetxattr will be triggered by p9_client_clunk, and unfortunately we
did not catch the error. This patch will catch the error to notify upper
caller.

p9_client_clunk (in 9p)
  p9_client_rpc(clnt, P9_TCLUNK, "d", fid->fid);
    v9fs_clunk (in qemu)
      put_fid
        free_fid
          v9fs_xattr_fid_clunk
            v9fs_co_lsetxattr
              s->ops->lsetxattr
                ext4_xattr_user_set (in host ext4 filesystem)

Link: http://lkml.kernel.org/r/5B57EACC.2060900@xxxxxxxxxx
Signed-off-by: Jun Piao <piaojun@xxxxxxxxxx>
Cc: Eric Van Hensbergen <ericvh@xxxxxxxxx>
Cc: Ron Minnich <rminnich@xxxxxxxxxx>
Cc: Latchesar Ionkov <lucho@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Dominique Martinet <dominique.martinet@xxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/9p/xattr.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/fs/9p/xattr.c
+++ b/fs/9p/xattr.c
@@ -121,7 +121,7 @@ int v9fs_fid_xattr_set(struct p9_fid *fi
 		   const void *value, size_t value_len, int flags)
 {
 	u64 offset = 0;
-	int retval, msize, write_count;
+	int retval, err, msize, write_count;
 
 	p9_debug(P9_DEBUG_VFS, "name = %s value_len = %zu flags = %d\n",
 		 name, value_len, flags);
@@ -158,7 +158,9 @@ int v9fs_fid_xattr_set(struct p9_fid *fi
 	}
 	retval = 0;
 err:
-	p9_client_clunk(fid);
+	err = p9_client_clunk(fid);
+	if (!retval && err)
+		retval = err;
 	return retval;
 }