[PATCH 09/11] btrfs: switch to RCU for device traversal in btrfs_ioctl_dev_info
From: David Sterba <dsterba@suse.com>
Date: 2017-10-31 17:46:42
Subsystem:
btrfs file system, filesystems (vfs and infrastructure), the rest · Maintainers:
Chris Mason, David Sterba, Alexander Viro, Christian Brauner, Linus Torvalds
We don't need to use the mutex as we do not modify the devices nor the list itself and just read some information: does not change during device lifetime: - devid - uuid - name (ie. the path) may change in parallel to the ioctl call, but can lead only to reporting inacurracy: - bytes_used - total_bytes Signed-off-by: David Sterba <dsterba@suse.com> --- fs/btrfs/ioctl.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index fd172a93d11a..f0a3308a72c5 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c@@ -2779,7 +2779,6 @@ static long btrfs_ioctl_dev_info(struct btrfs_fs_info *fs_info, { struct btrfs_ioctl_dev_info_args *di_args; struct btrfs_device *dev; - struct btrfs_fs_devices *fs_devices = fs_info->fs_devices; int ret = 0; char *s_uuid = NULL;
@@ -2790,7 +2789,7 @@ static long btrfs_ioctl_dev_info(struct btrfs_fs_info *fs_info, if (!btrfs_is_empty_uuid(di_args->uuid)) s_uuid = di_args->uuid; - mutex_lock(&fs_devices->device_list_mutex); + rcu_read_lock(); dev = btrfs_find_device(fs_info, di_args->devid, s_uuid, NULL); if (!dev) {
@@ -2805,17 +2804,15 @@ static long btrfs_ioctl_dev_info(struct btrfs_fs_info *fs_info, if (dev->name) { struct rcu_string *name; - rcu_read_lock(); name = rcu_dereference(dev->name); strncpy(di_args->path, name->str, sizeof(di_args->path)); - rcu_read_unlock(); di_args->path[sizeof(di_args->path) - 1] = 0; } else { di_args->path[0] = '\0'; } out: - mutex_unlock(&fs_devices->device_list_mutex); + rcu_read_unlock(); if (ret == 0 && copy_to_user(arg, di_args, sizeof(*di_args))) ret = -EFAULT;
--
2.14.0