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btrfs: do not call close_fs_devices in btrfs_rm_device

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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 simply decrement the  ->opened counter 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.

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Josef Bacik 2021-10-05 16:12:41 -04:00 committed by David Sterba
parent add9745adc
commit 8b41393fe7
1 changed files with 9 additions and 1 deletions
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10
fs/btrfs/volumes.c
View file

@ -2211,9 +2211,17 @@ 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->num_devices == 0) {
list_del_init(&cur_devices->seed_list);
close_fs_devices(cur_devices);
ASSERT(cur_devices->opened == 1);
cur_devices->opened--;
free_fs_devices(cur_devices);
}