[PATCH 04/11] 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 | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
index c0035fc0ec67..9b54a51ba860 100644
--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -776,13 +776,11 @@ static int __reada_start_for_fsdevs(struct btrfs_fs_devices *fs_devices)
 
 	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);
 
@@ -795,10 +793,13 @@ static void __reada_start_machine(struct btrfs_fs_info *fs_info)
 	int i;
 	u64 enqueued = 0;
 
+	mutex_lock(&fs_devices->device_list_mutex);
+
 	enqueued += __reada_start_for_fsdevs(fs_devices);
 	list_for_each_entry(seed_devs, &fs_devices->seed_list, seed_list)
 		enqueued += __reada_start_for_fsdevs(seed_devs);
 
+	mutex_unlock(&fs_devices->device_list_mutex);
 	if (enqueued == 0)
 		return;
 
-- 
2.25.1