| Message ID | 27fa361288b46bcc0f4b1225f7c76c96ce6dbe5f.1627419595.git.josef@toxicpanda.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2,1/7] btrfs: do not call close_fs_devices in btrfs_rm_device | expand |
On 28/07/2021 05:01, 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 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 <anand.jain@oracle.com> Thanks, Anand
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) { + ASSERT(cur_devices->opened == 1); 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 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(-)