[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>

fs/gfs2/incore.h

@@ -611,10 +611,6 @@ struct gfs2_sbd {
 	/* Log stuff */
 
 	spinlock_t sd_log_lock;
-	atomic_t sd_log_trans_count;
-	wait_queue_head_t sd_log_trans_wq;
-	atomic_t sd_log_flush_count;
-	wait_queue_head_t sd_log_flush_wq;
 
 	unsigned int sd_log_blks_reserved;
 	unsigned int sd_log_commited_buf;
@@ -643,7 +639,7 @@ struct gfs2_sbd {
 	int sd_log_idle;
 
 	unsigned long sd_log_flush_time;
-	struct mutex sd_log_flush_lock;
+	struct rw_semaphore sd_log_flush_lock;
 	struct list_head sd_log_flush_list;
 
 	unsigned int sd_log_flush_head;

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);
 }
 

fs/gfs2/ops_fstype.c

@@ -88,8 +88,6 @@ static struct gfs2_sbd *init_sbd(struct super_block *sb)
 	mutex_init(&sdp->sd_quota_mutex);
 
 	spin_lock_init(&sdp->sd_log_lock);
-	init_waitqueue_head(&sdp->sd_log_trans_wq);
-	init_waitqueue_head(&sdp->sd_log_flush_wq);
 
 	INIT_LIST_HEAD(&sdp->sd_log_le_gl);
 	INIT_LIST_HEAD(&sdp->sd_log_le_buf);
@@ -101,7 +99,7 @@ static struct gfs2_sbd *init_sbd(struct super_block *sb)
 	INIT_LIST_HEAD(&sdp->sd_ail1_list);
 	INIT_LIST_HEAD(&sdp->sd_ail2_list);
 
-	mutex_init(&sdp->sd_log_flush_lock);
+	init_rwsem(&sdp->sd_log_flush_lock);
 	INIT_LIST_HEAD(&sdp->sd_log_flush_list);
 
 	INIT_LIST_HEAD(&sdp->sd_revoke_list);

fs/gfs2/trans.c

@@ -74,10 +74,10 @@ int gfs2_trans_begin_i(struct gfs2_sbd *sdp, unsigned int blocks,
 
 	return 0;
 
- fail_gunlock:
+fail_gunlock:
 	gfs2_glock_dq(&tr->tr_t_gh);
 
- fail_holder_uninit:
+fail_holder_uninit:
 	gfs2_holder_uninit(&tr->tr_t_gh);
 	kfree(tr);