btrfs: reada: lock all seed/sprout devices in __reada_start_machine

On an fs mounted using a sprout device, the seed fs_devices are
maintained in a linked list under fs_info->fs_devices. Each seeds
fs_devices also has 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 belongs to sprout device_list_mutex instead of seed
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.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
index e209722..9d4f531 100644 (file)
--- 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;