[GFS2] Fix race in logging code

The log lock is dropped prior to io submittion, but
this exposes a hole in which the log data structures
may be going away due to a truncate.
Store the buffer head in a local pointer prior to
dropping the lock and relay on the buffer_head lock
for consitency on the buffer head.

Signed-Off-By: Russell Cattelan <cattelan@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 21 insertions, 15 deletions

diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index 8a654cd253dd..4d7f94d8c7bd 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -509,7 +509,7 @@ static void databuf_lo_before_commit(struct gfs2_sbd *sdp)
 {
         LIST_HEAD(started);
         struct gfs2_bufdata *bd1 = NULL, *bd2, *bdt;
-        struct buffer_head *bh = NULL;
+        struct buffer_head *bh = NULL,*bh1 = NULL;
         unsigned int offset = sizeof(struct gfs2_log_descriptor);
         struct gfs2_log_descriptor *ld;
         unsigned int limit;
@@ -537,8 +537,13 @@ static void databuf_lo_before_commit(struct gfs2_sbd *sdp)
                 list_for_each_entry_safe_continue(bd1, bdt,
                                                   &sdp->sd_log_le_databuf,
                                                   bd_le.le_list) {
+                        /* store off the buffer head in a local ptr since
+                         * gfs2_bufdata might change when we drop the log lock
+                         */
+                        bh1 = bd1->bd_bh;
+
                         /* An ordered write buffer */
-                        if (bd1->bd_bh && !buffer_pinned(bd1->bd_bh)) {
+                        if (bh1 && !buffer_pinned(bh1)) {
                                 list_move(&bd1->bd_le.le_list, &started);
                                 if (bd1 == bd2) {
                                         bd2 = NULL;
@@ -547,20 +552,21 @@ static void databuf_lo_before_commit(struct gfs2_sbd *sdp)
                                                         bd_le.le_list);
                                 }
                                 total_dbuf--;
-                                if (bd1->bd_bh) {
-                                        get_bh(bd1->bd_bh);
-                                        if (buffer_dirty(bd1->bd_bh)) {
+                                if (bh1) {
+                                        if (buffer_dirty(bh1)) {
+                                                get_bh(bh1);
+
                                                 gfs2_log_unlock(sdp);
-                                                wait_on_buffer(bd1->bd_bh);
-                                                ll_rw_block(WRITE, 1,
-                                                            &bd1->bd_bh);
+
+                                                ll_rw_block(SWRITE, 1, &bh1);
+                                                brelse(bh1);
+
                                                 gfs2_log_lock(sdp);
                                         }
-                                        brelse(bd1->bd_bh);
                                         continue;
                                 }
                                 continue;
-                        } else if (bd1->bd_bh) { /* A journaled buffer */
+                        } else if (bh1) { /* A journaled buffer */
                                 int magic;
                                 gfs2_log_unlock(sdp);
                                 if (!bh) {
@@ -582,16 +588,16 @@ static void databuf_lo_before_commit(struct gfs2_sbd *sdp)
                                         ld->ld_data2 = cpu_to_be32(0);
                                         memset(ld->ld_reserved, 0, sizeof(ld->ld_reserved));
                                 }
-                                magic = gfs2_check_magic(bd1->bd_bh);
-                                *ptr++ = cpu_to_be64(bd1->bd_bh->b_blocknr);
+                                magic = gfs2_check_magic(bh1);
+                                *ptr++ = cpu_to_be64(bh1->b_blocknr);
                                 *ptr++ = cpu_to_be64((__u64)magic);
-                                clear_buffer_escaped(bd1->bd_bh);
+                                clear_buffer_escaped(bh1);
                                 if (unlikely(magic != 0))
-                                        set_buffer_escaped(bd1->bd_bh);
+                                        set_buffer_escaped(bh1);
                                 gfs2_log_lock(sdp);
                                 if (n++ > num)
                                         break;
-                        } else if (!bd1->bd_bh) {
+                        } else if (!bh1) {
                                 total_dbuf--;
                                 sdp->sd_log_num_databuf--;
                                 list_del_init(&bd1->bd_le.le_list);