Btrfs: using rcu lock in the reader side of devices list

fs_devices->devices is only updated on remove and add device paths, so we can
use rcu to protect it in the reader side

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

1 files changed, 7 insertions, 7 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 4e53a4fc467f..deba3d9c8853 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1410,8 +1410,8 @@ 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) {
+        rcu_read_lock();
+        list_for_each_entry_rcu(device, &info->fs_devices->devices, dev_list) {
                 if (!device->bdev)
                         continue;
                 bdi = blk_get_backing_dev_info(device->bdev);
@@ -1420,7 +1420,7 @@ static int btrfs_congested_fn(void *congested_data, int bdi_bits)
                         break;
                 }
         }
-        mutex_unlock(&info->fs_devices->device_list_mutex);
+        rcu_read_unlock();
         return ret;
 }
 
@@ -2332,9 +2332,9 @@ int write_all_supers(struct btrfs_root *root, int max_mirrors)
         sb = &root->fs_info->super_for_commit;
         dev_item = &sb->dev_item;
 
-        mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
+        rcu_read_lock();
         head = &root->fs_info->fs_devices->devices;
-        list_for_each_entry(dev, head, dev_list) {
+        list_for_each_entry_rcu(dev, head, dev_list) {
                 if (!dev->bdev) {
                         total_errors++;
                         continue;
@@ -2367,7 +2367,7 @@ int write_all_supers(struct btrfs_root *root, int max_mirrors)
         }
 
         total_errors = 0;
-        list_for_each_entry(dev, head, dev_list) {
+        list_for_each_entry_rcu(dev, head, dev_list) {
                 if (!dev->bdev)
                         continue;
                 if (!dev->in_fs_metadata || !dev->writeable)
@@ -2377,7 +2377,7 @@ int write_all_supers(struct btrfs_root *root, int max_mirrors)
                 if (ret)
                         total_errors++;
         }
-        mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
+        rcu_read_unlock();
         if (total_errors > max_errors) {
                 printk(KERN_ERR "btrfs: %d errors while writing supers\n",
                        total_errors);