[10/11] btrfs: switch to RCU for device traversal in btrfs_ioctl_fs_info

Commit Message

David Sterba Oct. 31, 2017, 5:44 p.m. UTC

We don't need to use the mutex as we do not modify the devices nor the
list itself and just read information about device counts.
Move copying fsid out of the protected section, not applicable to RCU
same as the rest of the retrieved information.

Signed-off-by: David Sterba <[e-mail]>
---
 fs/btrfs/ioctl.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Patch

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index f0a3308a72c5..b15973cde0b6 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2753,16 +2753,16 @@  static long btrfs_ioctl_fs_info(struct btrfs_fs_info *fs_info,
 	if (!fi_args)
 		return -ENOMEM;
 
-	mutex_lock(&fs_devices->device_list_mutex);
+	rcu_read_lock();
 	fi_args->num_devices = fs_devices->num_devices;
-	memcpy(&fi_args->fsid, fs_info->fsid, sizeof(fi_args->fsid));
 
-	list_for_each_entry(device, &fs_devices->devices, dev_list) {
+	list_for_each_entry_rcu(device, &fs_devices->devices, dev_list) {
 		if (device->devid > fi_args->max_id)
 			fi_args->max_id = device->devid;
 	}
-	mutex_unlock(&fs_devices->device_list_mutex);
+	rcu_read_unlock();
 
+	memcpy(&fi_args->fsid, fs_info->fsid, sizeof(fi_args->fsid));
 	fi_args->nodesize = fs_info->nodesize;
 	fi_args->sectorsize = fs_info->sectorsize;
 	fi_args->clone_alignment = fs_info->sectorsize;