Btrfs: fix the race between reading and updating devices

On btrfs_congested_fn and __unplug_io_fn paths, we should hold
device_list_mutex to avoid remove/add device path to
update fs_devices->devices

On __btrfs_close_devices and btrfs_prepare_sprout paths, the devices in
fs_devices->devices or fs_devices->devices is updated, so we should hold
the mutex to avoid the reader side to reach them

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 64b289690f9d..4e53a4fc467f 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1410,6 +1410,7 @@ static int btrfs_congested_fn(void *congested_data, int bdi_bits)
         struct btrfs_device *device;
         struct backing_dev_info *bdi;
 
+        mutex_lock(&info->fs_devices->device_list_mutex);
         list_for_each_entry(device, &info->fs_devices->devices, dev_list) {
                 if (!device->bdev)
                         continue;
@@ -1419,6 +1420,7 @@ static int btrfs_congested_fn(void *congested_data, int bdi_bits)
                         break;
                 }
         }
+        mutex_unlock(&info->fs_devices->device_list_mutex);
         return ret;
 }