Btrfs: avoid unnecessary scrub workers allocation

We only allocate scrub workers if we pass all the necessary
checks, for example, there are no operation in progress.

Besides, move mutex lock protection outside of scrub_workers_get()
/scrub_workers_put().

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>

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 12009b4279ad1c1e3faad9e5353de1f86a0a4c9a..2544805544f0baf137c33de162c46f14b5ddf002 100644 (file)
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -2784,7 +2784,6 @@ static noinline_for_stack int scrub_workers_get(struct btrfs_fs_info *fs_info,
 {
        int ret = 0;
 
-       mutex_lock(&fs_info->scrub_lock);
        if (fs_info->scrub_workers_refcnt == 0) {
                if (is_dev_replace)
                        btrfs_init_workers(&fs_info->scrub_workers, "scrub", 1,
@@ -2814,21 +2813,17 @@ static noinline_for_stack int scrub_workers_get(struct btrfs_fs_info *fs_info,
        }
        ++fs_info->scrub_workers_refcnt;
 out:
-       mutex_unlock(&fs_info->scrub_lock);
-
        return ret;
 }
 
 static noinline_for_stack void scrub_workers_put(struct btrfs_fs_info *fs_info)
 {
-       mutex_lock(&fs_info->scrub_lock);
        if (--fs_info->scrub_workers_refcnt == 0) {
                btrfs_stop_workers(&fs_info->scrub_workers);
                btrfs_stop_workers(&fs_info->scrub_wr_completion_workers);
                btrfs_stop_workers(&fs_info->scrub_nocow_workers);
        }
        WARN_ON(fs_info->scrub_workers_refcnt < 0);
-       mutex_unlock(&fs_info->scrub_lock);
 }
 
 int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
@@ -2889,23 +2884,18 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
                return -EINVAL;
        }
 
-       ret = scrub_workers_get(fs_info, is_dev_replace);
-       if (ret)
-               return ret;
 
        mutex_lock(&fs_info->fs_devices->device_list_mutex);
        dev = btrfs_find_device(fs_info, devid, NULL, NULL);
        if (!dev || (dev->missing && !is_dev_replace)) {
                mutex_unlock(&fs_info->fs_devices->device_list_mutex);
-               scrub_workers_put(fs_info);
                return -ENODEV;
        }
-       mutex_lock(&fs_info->scrub_lock);
 
+       mutex_lock(&fs_info->scrub_lock);
        if (!dev->in_fs_metadata || dev->is_tgtdev_for_dev_replace) {
                mutex_unlock(&fs_info->scrub_lock);
                mutex_unlock(&fs_info->fs_devices->device_list_mutex);
-               scrub_workers_put(fs_info);
                return -EIO;
        }
 
@@ -2916,10 +2906,17 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
                btrfs_dev_replace_unlock(&fs_info->dev_replace);
                mutex_unlock(&fs_info->scrub_lock);
                mutex_unlock(&fs_info->fs_devices->device_list_mutex);
-               scrub_workers_put(fs_info);
                return -EINPROGRESS;
        }
        btrfs_dev_replace_unlock(&fs_info->dev_replace);
+
+       ret = scrub_workers_get(fs_info, is_dev_replace);
+       if (ret) {
+               mutex_unlock(&fs_info->scrub_lock);
+               mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+               return ret;
+       }
+
        sctx = scrub_setup_ctx(dev, is_dev_replace);
        if (IS_ERR(sctx)) {
                mutex_unlock(&fs_info->scrub_lock);
@@ -2957,10 +2954,10 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
 
        mutex_lock(&fs_info->scrub_lock);
        dev->scrub_device = NULL;
+       scrub_workers_put(fs_info);
        mutex_unlock(&fs_info->scrub_lock);
 
        scrub_free_ctx(sctx);
-       scrub_workers_put(fs_info);
 
        return ret;
 }