[GFS2] Update locking in log.c

Replace the lock_for_trans()/lock_for_flush() functions with an rwsem.
In fact the sd_log_flush_lock becomes an rwsem (the write part of it)
and is extended slightly to cover everything that the lock_for_flush()
used to cover. The read part of the lock is instead of lock_for_trans().

This corrects the races in the original code and reduces the code size.

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

1 files changed, 18 insertions, 49 deletions

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 16c14441a371..b103d9acf40d 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -29,32 +29,6 @@
 
 #define PULL 1
 
-static void lock_for_trans(struct gfs2_sbd *sdp)
-{
-        wait_event(sdp->sd_log_trans_wq, atomic_read(&sdp->sd_log_flush_count) ? 0 : 1);
-        atomic_inc(&sdp->sd_log_trans_count);
-}
-
-static void unlock_from_trans(struct gfs2_sbd *sdp)
-{
-        gfs2_assert_warn(sdp, atomic_read(&sdp->sd_log_trans_count));
-        if (atomic_dec_and_test(&sdp->sd_log_trans_count))
-                wake_up(&sdp->sd_log_flush_wq);
-}
-
-static void gfs2_lock_for_flush(struct gfs2_sbd *sdp)
-{
-        atomic_inc(&sdp->sd_log_flush_count);
-        wait_event(sdp->sd_log_flush_wq, atomic_read(&sdp->sd_log_trans_count) ? 0 : 1);
-}
-
-static void gfs2_unlock_from_flush(struct gfs2_sbd *sdp)
-{
-        gfs2_assert_warn(sdp, atomic_read(&sdp->sd_log_flush_count));
-        if (atomic_dec_and_test(&sdp->sd_log_flush_count))
-                wake_up(&sdp->sd_log_trans_wq);
-}
-
 /**
  * gfs2_struct2blk - compute stuff
  * @sdp: the filesystem
@@ -109,9 +83,8 @@ void gfs2_ail1_start(struct gfs2_sbd *sdp, int flags)
                 first = NULL;
 
         for (;;) {
-                if (first &&
-                    (head->prev != first ||
-                     gfs2_ail1_empty_one(sdp, first_ai, 0)))
+                if (first && (head->prev != first ||
+                              gfs2_ail1_empty_one(sdp, first_ai, 0)))
                         break;
 
                 for (tmp = head->prev; tmp != head; tmp = tmp->prev) {
@@ -194,23 +167,21 @@ int gfs2_log_reserve(struct gfs2_sbd *sdp, unsigned int blks)
                 return -EINVAL;
 
         mutex_lock(&sdp->sd_log_reserve_mutex);
-        for (;;) {
-                gfs2_log_lock(sdp);
-                if (sdp->sd_log_blks_free > blks) {
-                        sdp->sd_log_blks_free -= blks;
-                        gfs2_log_unlock(sdp);
-                        mutex_unlock(&sdp->sd_log_reserve_mutex);
-                        break;
-                }
-
+        gfs2_log_lock(sdp);
+        while(sdp->sd_log_blks_free <= blks) {
                 gfs2_log_unlock(sdp);
                 gfs2_ail1_empty(sdp, 0);
                 gfs2_log_flush(sdp);
 
                 if (try++)
                         gfs2_ail1_start(sdp, 0);
+                gfs2_log_lock(sdp);
         }
-        lock_for_trans(sdp);
+        sdp->sd_log_blks_free -= blks;
+        gfs2_log_unlock(sdp);
+        mutex_unlock(&sdp->sd_log_reserve_mutex);
+
+        down_read(&sdp->sd_log_flush_lock);
 
         return 0;
 }
@@ -224,7 +195,7 @@ int gfs2_log_reserve(struct gfs2_sbd *sdp, unsigned int blks)
 
 void gfs2_log_release(struct gfs2_sbd *sdp, unsigned int blks)
 {
-        unlock_from_trans(sdp);
+        up_read(&sdp->sd_log_flush_lock);
 
         gfs2_log_lock(sdp);
         sdp->sd_log_blks_free += blks;
@@ -474,20 +445,20 @@ void gfs2_log_flush_i(struct gfs2_sbd *sdp, struct gfs2_glock *gl)
         ai = kzalloc(sizeof(struct gfs2_ail), GFP_NOFS | __GFP_NOFAIL);
         INIT_LIST_HEAD(&ai->ai_ail1_list);
         INIT_LIST_HEAD(&ai->ai_ail2_list);
-        gfs2_lock_for_flush(sdp);
+
+        down_write(&sdp->sd_log_flush_lock);
 
         if (gl) {
                 gfs2_log_lock(sdp);
                 if (list_empty(&gl->gl_le.le_list)) {
                         gfs2_log_unlock(sdp);
-                        gfs2_unlock_from_flush(sdp);
+                        up_write(&sdp->sd_log_flush_lock);
                         kfree(ai);
                         return;
                 }
                 gfs2_log_unlock(sdp);
         }
 
-        mutex_lock(&sdp->sd_log_flush_lock);
 
         gfs2_assert_withdraw(sdp,
                         sdp->sd_log_num_buf == sdp->sd_log_commited_buf);
@@ -519,9 +490,8 @@ void gfs2_log_flush_i(struct gfs2_sbd *sdp, struct gfs2_glock *gl)
         }
         gfs2_log_unlock(sdp);
 
-        mutex_unlock(&sdp->sd_log_flush_lock);
         sdp->sd_vfs->s_dirt = 0;
-        gfs2_unlock_from_flush(sdp);
+        up_write(&sdp->sd_log_flush_lock);
 
         kfree(ai);
 }
@@ -573,7 +543,7 @@ void gfs2_log_commit(struct gfs2_sbd *sdp, struct gfs2_trans *tr)
         lops_incore_commit(sdp, tr);
 
         sdp->sd_vfs->s_dirt = 1;
-        unlock_from_trans(sdp);
+        up_read(&sdp->sd_log_flush_lock);
 
         gfs2_log_lock(sdp);
         if (sdp->sd_log_num_buf > gfs2_tune_get(sdp, gt_incore_log_blocks)) {
@@ -591,9 +561,8 @@ void gfs2_log_commit(struct gfs2_sbd *sdp, struct gfs2_trans *tr)
 
 void gfs2_log_shutdown(struct gfs2_sbd *sdp)
 {
-        mutex_lock(&sdp->sd_log_flush_lock);
+        down_write(&sdp->sd_log_flush_lock);
 
-        gfs2_assert_withdraw(sdp, !atomic_read(&sdp->sd_log_trans_count));
         gfs2_assert_withdraw(sdp, !sdp->sd_log_blks_reserved);
         gfs2_assert_withdraw(sdp, !sdp->sd_log_num_gl);
         gfs2_assert_withdraw(sdp, !sdp->sd_log_num_buf);
@@ -618,6 +587,6 @@ void gfs2_log_shutdown(struct gfs2_sbd *sdp)
                 sdp->sd_log_wraps++;
         sdp->sd_log_tail = sdp->sd_log_head;
 
-        mutex_unlock(&sdp->sd_log_flush_lock);
+        up_write(&sdp->sd_log_flush_lock);
 }