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, 4 insertions, 3 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index ce773fb736a1..0de71feb8e1c 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -281,8 +281,9 @@ static noinline int btrfs_ioctl_fitrim(struct file *file, void __user *arg)
         if (!capable(CAP_SYS_ADMIN))
                 return -EPERM;
 
-        mutex_lock(&fs_info->fs_devices->device_list_mutex);
-        list_for_each_entry(device, &fs_info->fs_devices->devices, dev_list) {
+        rcu_read_lock();
+        list_for_each_entry_rcu(device, &fs_info->fs_devices->devices,
+                                dev_list) {
                 if (!device->bdev)
                         continue;
                 q = bdev_get_queue(device->bdev);
@@ -292,7 +293,7 @@ static noinline int btrfs_ioctl_fitrim(struct file *file, void __user *arg)
                                      minlen);
                 }
         }
-        mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+        rcu_read_unlock();
         if (!num_devices)
                 return -EOPNOTSUPP;