From: Steven Whitehouse <swhiteho@redhat.com>
Subject: [RHEL5] [GFS2] Fix recursive locking in gfs2_permission
Date: Thu, 07 Dec 2006 11:45:23 +0000
Bugzilla: 218478
Message-Id: <1165491923.3752.839.camel@quoit.chygwyn.com>
Changelog: GFS2: Fix recursive locking in gfs2_permission


Hi,

The following patch fixes bz #218478, the bz referred to below is the one
for Fedora. This patch (well almost this patch I had to change one line by
hand to get it to apply to RHEL5 after extracting it from git) is in the
upstream git tree and about to be applied to Linus' kernel,

Steve.

>From 300c7d75f3a5e8edd3e390ccd56b808f3fb14e33 Mon Sep 17 00:00:00 2001

Since gfs2_permission may be called either from the VFS (in which case
we need to obtain a shared glock) or from GFS2 (in which case we already
have a glock) we need to test to see whether or not a lock is required.
The original test was buggy due to a potential race. This one should
be safe.

This fixes Red Hat bugzilla #217129

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
---
 fs/gfs2/ops_inode.c |   19 +++++++++++++------
 1 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/fs/gfs2/ops_inode.c b/fs/gfs2/ops_inode.c
index b247f25..fd9fee2 100644
--- a/fs/gfs2/ops_inode.c
+++ b/fs/gfs2/ops_inode.c
@@ -835,6 +835,10 @@ static void *gfs2_follow_link(struct den
  * @mask:
  * @nd: passed from Linux VFS, ignored by us
  *
+ * This may be called from the VFS directly, or from within GFS2 with the
+ * inode locked, so we look to see if the glock is already locked and only
+ * lock the glock if its not already been done.
+ *
  * Returns: errno
  */
 
@@ -843,15 +847,18 @@ static int gfs2_permission(struct inode 
 	struct gfs2_inode *ip = GFS2_I(inode);
 	struct gfs2_holder i_gh;
 	int error;
+	int unlock = 0;
 
-	if (ip->i_vn == ip->i_gl->gl_vn)
-		return generic_permission(inode, mask, gfs2_check_acl);
+	if (gfs2_glock_is_locked_by_me(ip->i_gl) == 0) {
+		error = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED, LM_FLAG_ANY, &i_gh);
+		if (error)
+			return error;
+		unlock = 1;
+	}
 
-	error = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED, LM_FLAG_ANY, &i_gh);
-	if (!error) {
-		error = generic_permission(inode, mask, gfs2_check_acl_locked);
+	error = generic_permission(inode, mask, gfs2_check_acl_locked);
+	if (unlock)
 		gfs2_glock_dq_uninit(&i_gh);
-	}
 
 	return error;
 }
-- 
1.4.1