From c5593ca3c8a82eb397804e22a34d2c7061b55f56 Mon Sep 17 00:00:00 2001 From: David Sterba Date: Fri, 16 Jun 2017 00:09:21 +0200 Subject: [PATCH] btrfs: switch to RCU for device traversal in btrfs_ioctl_dev_info 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 --- 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 64b947487ca6..f1884c075cd3 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -2775,7 +2775,6 @@ 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; @@ -2786,7 +2785,7 @@ 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) { @@ -2801,17 +2800,15 @@ 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; -- 2.11.0