[PATCH 1/7] btrfs: reada: use sprout device_list_mutex

[Anand Jain <anand.jain@oracle.com>]

On an fs mounted using a sprout-device, the seed fs_devices are maintained
in a linked list under fs_info->fs_devices. Each seed's fs_devices also
have device_list_mutex initialized to protect against the potential race
with delete threads. But the delete thread (at btrfs_rm_device()) is holding
the fs_info::fs_devices::device_list_mutex mutex which is sprout's
device_list_mutex instead of seed's device_list_mutex. Moreover, there
aren't any significient benefits in using the seed::device_list_mutex
instead of sprout::device_list_mutex.

So this patch converts them of using the seed::device_list_mutex to
sprout::device_list_mutex.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 fs/btrfs/reada.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
index 243a2e44526e..c4667410b3fa 100644
--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -775,22 +775,22 @@ static void __reada_start_machine(struct btrfs_fs_info *fs_info)
 	u64 total = 0;
 	int i;
 
+	mutex_lock(&fs_info->fs_devices->device_list_mutex);
 again:
 	do {
 		enqueued = 0;
-		mutex_lock(&fs_devices->device_list_mutex);
 		list_for_each_entry(device, &fs_devices->devices, dev_list) {
 			if (atomic_read(&device->reada_in_flight) <
 			    MAX_IN_FLIGHT)
 				enqueued += reada_start_machine_dev(device);
 		}
-		mutex_unlock(&fs_devices->device_list_mutex);
 		total += enqueued;
 	} while (enqueued && total < 10000);
 	if (fs_devices->seed) {
 		fs_devices = fs_devices->seed;
 		goto again;
 	}
+	mutex_unlock(&fs_info->fs_devices->device_list_mutex);
 
 	if (enqueued == 0)
 		return;
-- 
2.18.2