[PATCH 2/8] btrfs: Reduce critical section in btrfs_init_dev_replace_tgtdev

[Nikolay Borisov]

There is no point in holding btrfs_fs_devices::device_list_mutex
while initialising fields of the not-yet-published device. Instead,
hold the mutex only when the newly initialised device is being
published. I think holding device_list_mutex here is redundant
altogether, because at this point BTRFS_FS_EXCL_OP is set which
prevents device removal/addition/balance/resize to occur.

Signed-off-by: Nikolay Borisov <nbori...@suse.com>
---
 fs/btrfs/dev-replace.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index c738ba460682..ac6600a00188 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -237,7 +237,6 @@ static int btrfs_init_dev_replace_tgtdev(struct 
btrfs_fs_info *fs_info,
        }
        rcu_assign_pointer(device->name, name);
 
-       mutex_lock(&fs_info->fs_devices->device_list_mutex);
        set_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
        device->generation = 0;
        device->io_width = fs_info->sectorsize;
@@ -256,6 +255,8 @@ static int btrfs_init_dev_replace_tgtdev(struct 
btrfs_fs_info *fs_info,
        device->dev_stats_valid = 1;
        set_blocksize(device->bdev, BTRFS_BDEV_BLOCKSIZE);
        device->fs_devices = fs_info->fs_devices;
+
+       mutex_lock(&fs_info->fs_devices->device_list_mutex);
        list_add(&device->dev_list, &fs_info->fs_devices->devices);
        fs_info->fs_devices->num_devices++;
        fs_info->fs_devices->open_devices++;
-- 
2.17.1