From: Abhijith Das <adas@redhat.com>
Date: Tue, 4 Dec 2007 01:25:00 -0600
Subject: [gfs2] recursive locking on rgrp in gfs2_rename
Message-id: 475500CC.3030209@redhat.com
O-Subject: [RHEL5.2][PATCH] GFS2 : bz 404711 - Recursive locking on rgrp in gfs2_rename causes kernel BUG
Bugzilla: 404711

The first lock is requested to unlink an already existing
inode (replacing a file) and the second lock is requested when the destination
directory needs to alloc some space. It is rare that these two events happen
during the same rename call, and even more rare that these two instances try to
lock the same rgrp. It is, however, possible.

This patch checks for already locked rgrp the second time around, thereby avoiding
the recursive locking.

Signed-off-by: Abhijith Das <adas@redhat.com>

Acked-by: Steven Whitehouse <swhiteho@redhat.com>
Acked-by: Bob Peterson <rpeterso@redhat.com>

diff --git a/fs/gfs2/rgrp.c b/fs/gfs2/rgrp.c
index 708c287..4fc56b9 100644
--- a/fs/gfs2/rgrp.c
+++ b/fs/gfs2/rgrp.c
@@ -1063,22 +1063,30 @@ static struct inode *get_local_rgrp(struct gfs2_inode *ip, u64 *last_unlinked)
 	int flags = LM_FLAG_TRY;
 	int skipped = 0;
 	int loops = 0;
-	int error;
+	int error, rg_locked;
 
 	/* Try recently successful rgrps */
 
 	rgd = recent_rgrp_first(sdp, ip->i_last_rg_alloc);
 
 	while (rgd) {
-		error = gfs2_glock_nq_init(rgd->rd_gl, LM_ST_EXCLUSIVE,
-					   LM_FLAG_TRY, &al->al_rgd_gh);
+		rg_locked = 0;
+
+		if (gfs2_glock_is_locked_by_me(rgd->rd_gl)) {
+			rg_locked = 1;
+			error = 0;
+		} else {
+			error = gfs2_glock_nq_init(rgd->rd_gl, LM_ST_EXCLUSIVE,
+						   LM_FLAG_TRY, &al->al_rgd_gh);
+		}
 		switch (error) {
 		case 0:
 			if (try_rgrp_fit(rgd, al))
 				goto out;
 			if (rgd->rd_flags & GFS2_RDF_CHECK)
 				inode = try_rgrp_unlink(rgd, last_unlinked);
-			gfs2_glock_dq_uninit(&al->al_rgd_gh);
+			if (!rg_locked)
+				gfs2_glock_dq_uninit(&al->al_rgd_gh);
 			if (inode)
 				return inode;
 			rgd = recent_rgrp_next(rgd, 1);
@@ -1098,15 +1106,23 @@ static struct inode *get_local_rgrp(struct gfs2_inode *ip, u64 *last_unlinked)
 	begin = rgd = forward_rgrp_get(sdp);
 
 	for (;;) {
-		error = gfs2_glock_nq_init(rgd->rd_gl, LM_ST_EXCLUSIVE, flags,
-					  &al->al_rgd_gh);
+		rg_locked = 0;
+
+		if (gfs2_glock_is_locked_by_me(rgd->rd_gl)) {
+			rg_locked = 1;
+			error = 0;
+		} else {
+			error = gfs2_glock_nq_init(rgd->rd_gl, LM_ST_EXCLUSIVE, flags,
+						   &al->al_rgd_gh);
+		}
 		switch (error) {
 		case 0:
 			if (try_rgrp_fit(rgd, al))
 				goto out;
 			if (rgd->rd_flags & GFS2_RDF_CHECK)
 				inode = try_rgrp_unlink(rgd, last_unlinked);
-			gfs2_glock_dq_uninit(&al->al_rgd_gh);
+			if (!rg_locked)
+				gfs2_glock_dq_uninit(&al->al_rgd_gh);
 			if (inode)
 				return inode;
 			break;
@@ -1213,7 +1229,8 @@ void gfs2_inplace_release(struct gfs2_inode *ip)
 			     al->al_line);
 
 	al->al_rgd = NULL;
-	gfs2_glock_dq_uninit(&al->al_rgd_gh);
+	if (al->al_rgd_gh.gh_gl)
+		gfs2_glock_dq_uninit(&al->al_rgd_gh);
 	if (ip != GFS2_I(sdp->sd_rindex))
 		gfs2_glock_dq_uninit(&al->al_ri_gh);
 }