Messages in this thread | | | Date | Wed, 28 Jul 2021 14:58:05 +0200 | From | David Sterba <> | Subject | Re: [PATCH v2] btrfs: fix rw device counting in __btrfs_free_extra_devids |
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On Tue, Jul 27, 2021 at 03:13:03PM +0800, Desmond Cheong Zhi Xi wrote: > When removing a writeable device in __btrfs_free_extra_devids, the rw > device count should be decremented. > > This error was caught by Syzbot which reported a warning in > close_fs_devices because fs_devices->rw_devices was not 0 after > closing all devices. Here is the call trace that was observed: > > btrfs_mount_root(): > btrfs_scan_one_device(): > device_list_add(); <---------------- device added > btrfs_open_devices(): > open_fs_devices(): > btrfs_open_one_device(); <-------- writable device opened, > rw device count ++ > btrfs_fill_super(): > open_ctree(): > btrfs_free_extra_devids(): > __btrfs_free_extra_devids(); <--- writable device removed, > rw device count not decremented > fail_tree_roots: > btrfs_close_devices(): > close_fs_devices(); <------- rw device count off by 1 > > As a note, prior to commit cf89af146b7e ("btrfs: dev-replace: fail > mount if we don't have replace item with target device"), rw_devices > was decremented on removing a writable device in > __btrfs_free_extra_devids only if the BTRFS_DEV_STATE_REPLACE_TGT bit > was not set for the device. However, this check does not need to be > reinstated as it is now redundant and incorrect. > > In __btrfs_free_extra_devids, we skip removing the device if it is the > target for replacement. This is done by checking whether device->devid > == BTRFS_DEV_REPLACE_DEVID. Since BTRFS_DEV_STATE_REPLACE_TGT is set > only on the device with devid BTRFS_DEV_REPLACE_DEVID, no devices > should have the BTRFS_DEV_STATE_REPLACE_TGT bit set after the check, > and so it's redundant to test for that bit. > > Additionally, following commit 82372bc816d7 ("Btrfs: make > the logic of source device removing more clear"), rw_devices is > incremented whenever a writeable device is added to the alloc > list (including the target device in btrfs_dev_replace_finishing), so > all removals of writable devices from the alloc list should also be > accompanied by a decrement to rw_devices. > > Fixes: cf89af146b7e ("btrfs: dev-replace: fail mount if we don't have replace item with target device") > Reported-by: syzbot+a70e2ad0879f160b9217@syzkaller.appspotmail.com > Tested-by: syzbot+a70e2ad0879f160b9217@syzkaller.appspotmail.com > Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> > Reviewed-by: Anand Jain <anand.jain@oracle.com>
Added to misc-next, thanks.
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