From f4cfa9bdd40c038ac901fbf3c57ab63e9e8eb949 Mon Sep 17 00:00:00 2001 From: Nikolay Borisov Date: Wed, 22 Jul 2020 11:09:22 +0300 Subject: [PATCH] btrfs: use RCU for quick device check in btrfs_init_new_device When adding a new device there's a mandatory check to see if a device is being duplicated to the filesystem it's added to. Since this is a read-only operations not necessary to take device_list_mutex and can simply make do with an rcu-readlock. Using just RCU is safe because there won't be another device add delete running in parallel as btrfs_init_new_device is called only from btrfs_ioctl_add_dev. Signed-off-by: Nikolay Borisov Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/volumes.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 29c6f0154c62c..5449e3899e672 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -2515,16 +2515,15 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path filemap_write_and_wait(bdev->bd_inode->i_mapping); - mutex_lock(&fs_devices->device_list_mutex); - list_for_each_entry(device, &fs_devices->devices, dev_list) { + rcu_read_lock(); + list_for_each_entry_rcu(device, &fs_devices->devices, dev_list) { if (device->bdev == bdev) { ret = -EEXIST; - mutex_unlock( - &fs_devices->device_list_mutex); + rcu_read_unlock(); goto error; } } - mutex_unlock(&fs_devices->device_list_mutex); + rcu_read_unlock(); device = btrfs_alloc_device(fs_info, NULL, NULL); if (IS_ERR(device)) { -- 2.30.2