| Message ID | 326bb4ecde587f0f3f4884b65d17951661a0ca77.1633367810.git.josef@toxicpanda.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Fix lockdep issues around device removal | expand |
On 05/10/2021 01:19, Josef Bacik wrote: > 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. > David, You might want to add this patch before commit e197aab25da2 (btrfs: do not take the uuid_mutex in btrfs_rm_device) in the misc-next. As this patch is preparatory of it. > Signed-off-by: Josef Bacik <josef@toxicpanda.com> Reviewed-by: Anand Jain <anand.jain@oralce.com> Thx, Anand > --- > fs/btrfs/volumes.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c > index 0941f61d8071..5f19d0863094 100644 > --- a/fs/btrfs/volumes.c > +++ b/fs/btrfs/volumes.c > @@ -2211,9 +2211,16 @@ 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); > + cur_devices->opened--; > free_fs_devices(cur_devices); > } > >
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 0941f61d8071..5f19d0863094 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -2211,9 +2211,16 @@ 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); + cur_devices->opened--; free_fs_devices(cur_devices); }
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. Signed-off-by: Josef Bacik <josef@toxicpanda.com> --- fs/btrfs/volumes.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)