Btrfs: remove scrub_super_lock holding in btrfs_sync_log()

Originally, we introduced scrub_super_lock to synchronize
tree log code with scrubbing super.

However we can replace scrub_super_lock with device_list_mutex,
because writing super will hold this mutex, this will reduce an extra
lock holding when writing supers in sync log code.

Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

5 files changed, 8 insertions, 20 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 9f5e1cfb0209..34279665fd69 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1586,7 +1586,6 @@ struct btrfs_fs_info {
         atomic_t scrubs_paused;
         atomic_t scrub_cancel_req;
         wait_queue_head_t scrub_pause_wait;
-        struct rw_semaphore scrub_super_lock;
         int scrub_workers_refcnt;
         struct btrfs_workers scrub_workers;
         struct btrfs_workers scrub_wr_completion_workers;
@@ -3950,9 +3949,7 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
                     u64 end, struct btrfs_scrub_progress *progress,
                     int readonly, int is_dev_replace);
 void btrfs_scrub_pause(struct btrfs_root *root);
-void btrfs_scrub_pause_super(struct btrfs_root *root);
 void btrfs_scrub_continue(struct btrfs_root *root);
-void btrfs_scrub_continue_super(struct btrfs_root *root);
 int btrfs_scrub_cancel(struct btrfs_fs_info *info);
 int btrfs_scrub_cancel_dev(struct btrfs_fs_info *info,
                            struct btrfs_device *dev);
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 62c4aba221bb..a3ad3a27944d 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2250,7 +2250,6 @@ int open_ctree(struct super_block *sb,
         atomic_set(&fs_info->scrubs_paused, 0);
         atomic_set(&fs_info->scrub_cancel_req, 0);
         init_waitqueue_head(&fs_info->scrub_pause_wait);
-        init_rwsem(&fs_info->scrub_super_lock);
         fs_info->scrub_workers_refcnt = 0;
 #ifdef CONFIG_BTRFS_FS_CHECK_INTEGRITY
         fs_info->check_integrity_print_mask = 0;
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index f21e2df89bc2..12009b4279ad 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -2932,13 +2932,15 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
 
         atomic_inc(&fs_info->scrubs_running);
         mutex_unlock(&fs_info->scrub_lock);
-        mutex_unlock(&fs_info->fs_devices->device_list_mutex);
 
         if (!is_dev_replace) {
-                down_read(&fs_info->scrub_super_lock);
+                /*
+                 * by holding device list mutex, we can
+                 * kick off writing super in log tree sync.
+                 */
                 ret = scrub_supers(sctx, dev);
-                up_read(&fs_info->scrub_super_lock);
         }
+        mutex_unlock(&fs_info->fs_devices->device_list_mutex);
 
         if (!ret)
                 ret = scrub_enumerate_chunks(sctx, dev, start, end,
@@ -2988,16 +2990,6 @@ void btrfs_scrub_continue(struct btrfs_root *root)
         wake_up(&fs_info->scrub_pause_wait);
 }
 
-void btrfs_scrub_pause_super(struct btrfs_root *root)
-{
-        down_write(&root->fs_info->scrub_super_lock);
-}
-
-void btrfs_scrub_continue_super(struct btrfs_root *root)
-{
-        up_write(&root->fs_info->scrub_super_lock);
-}
-
 int btrfs_scrub_cancel(struct btrfs_fs_info *fs_info)
 {
         mutex_lock(&fs_info->scrub_lock);
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index f98002ed32b1..257cbae8c948 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -2586,9 +2586,7 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
          * the running transaction open, so a full commit can't hop
          * in and cause problems either.
          */
-        btrfs_scrub_pause_super(root);
         ret = write_ctree_super(trans, root->fs_info->tree_root, 1);
-        btrfs_scrub_continue_super(root);
         if (ret) {
                 btrfs_abort_transaction(trans, root, ret);
                 goto out_wake_log_root;
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index b72f540c8b29..49e0ff01143f 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -132,7 +132,9 @@ struct btrfs_fs_devices {
 
         /* all of the devices in the FS, protected by a mutex
          * so we can safely walk it to write out the supers without
-         * worrying about add/remove by the multi-device code
+         * worrying about add/remove by the multi-device code.
+         * Scrubbing super can kick off supers writing by holding
+         * this mutex lock.
          */
         struct mutex device_list_mutex;
         struct list_head devices;