[GFS2] patch to check for recursive lock requests in gfs2_rename code path

A certain scenario in the rename code path triggers a kernel BUG()
because it accidentally does recursive locking 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.
https://bugzilla.redhat.com/show_bug.cgi?id=404711

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

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);
 }