On 04/04/2018 02:34 AM, David Sterba wrote:
The volume mutex does not protect against anything in this case, the
comment about scrub is right but not related to locking and looks
confusing. The comment in btrfs_find_device_missing_or_by_path is wrong
and confusing too.
The device_list_mutex is not held here to protect device lookup, but in
this case device replace cannot run in parallel with device removal (due
to exclusive op protection), so we don't need further locking here.
Agreed, usage of device_list_mutex and volume_mutex is kind of redundant.
There are unfinished features in btrfs volume, such as device offline
while it was mounted (patches in the ML).
It's better to replace volume_mutex with device_list_mutex instead of
removing it, as we might need it in the context mentioned above.
Or it's not a good idea to clean up until all the features are in place
otherwise we end up adding the locks again at some point.
Thanks, Anand
Signed-off-by: David Sterba <dste...@suse.com>
---
fs/btrfs/dev-replace.c | 7 +------
fs/btrfs/volumes.c | 4 ----
2 files changed, 1 insertion(+), 10 deletions(-)
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 346bd460f8e7..ba011af9b0d2 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -426,18 +426,13 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
struct btrfs_device *tgt_device = NULL;
struct btrfs_device *src_device = NULL;
- /* the disk copy procedure reuses the scrub code */
- mutex_lock(&fs_info->volume_mutex);
ret = btrfs_find_device_by_devspec(fs_info, srcdevid,
srcdev_name, &src_device);
- if (ret) {
- mutex_unlock(&fs_info->volume_mutex);
+ if (ret)
return ret;
- }
ret = btrfs_init_dev_replace_tgtdev(fs_info, tgtdev_name,
src_device, &tgt_device);
- mutex_unlock(&fs_info->volume_mutex);
if (ret)
return ret;
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index b073ab4c3c70..0ae29cd69363 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2198,10 +2198,6 @@ int btrfs_find_device_missing_or_by_path(struct
btrfs_fs_info *fs_info,
struct btrfs_device *tmp;
devices = &fs_info->fs_devices->devices;
- /*
- * It is safe to read the devices since the volume_mutex
- * is held by the caller.
- */
list_for_each_entry(tmp, devices, dev_list) {
if (test_bit(BTRFS_DEV_STATE_IN_FS_METADATA,
&tmp->dev_state) && !tmp->bdev) {
--
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