Re: [PATCH v2 1/7] btrfs: do not call close_fs_devices in btrfs_rm_device
From: Anand Jain <hidden>
Date: 2021-09-01 08:13:40
On 28/07/2021 05:01, Josef Bacik wrote:
quoted hunk ↗ jump to hunk
There's a subtle case where if we're removing the seed device from a file system we need to free its private copy of the fs_devices. However we do not need to call close_fs_devices(), because at this point there are no devices left to close as we've closed the last one. The only thing that close_fs_devices() does is decrement ->opened, which should be 1. We want to avoid calling close_fs_devices() here because it has a lockdep_assert_held(&uuid_mutex), and we are going to stop holding the uuid_mutex in this path. So add an assert for the ->opened counter and simply decrement it like we should, and then clean up like normal. Also add a comment explaining what we're doing here as I initially removed this code erroneously. Signed-off-by: Josef Bacik <josef@toxicpanda.com> --- fs/btrfs/volumes.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 86846d6e58d0..5217b93172b4 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c@@ -2200,9 +2200,17 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path, synchronize_rcu(); btrfs_free_device(device); + /* + * This can happen if cur_devices is the private seed devices list. We + * cannot call close_fs_devices() here because it expects the uuid_mutex + * to be held, but in fact we don't need that for the private + * seed_devices, we can simply decrement cur_devices->opened and then + * remove it from our list and free the fs_devices. + */
if (cur_devices->open_devices == 0) {We should in fact use cur_devices->num_devices == 0 here. Sent a patch [1] to fix it. [1] https://patchwork.kernel.org/project/linux-btrfs/patch/d9c89b1740a876b3851fcf358f22809aa7f1ad2a.1630478246.git.anand.jain@oracle.com/
+ ASSERT(cur_devices->opened == 1);
We don't need to assert(). free_fs_devices() has a warning for it.
WARN_ON(fs_devices->opened);
list_del_init(&cur_devices->seed_list); - close_fs_devices(cur_devices); + cur_devices->opened--; free_fs_devices(cur_devices); }
With the above two fixed. Reviewed-by: Anand Jain <redacted> Thanks, Anand