[PATCH v2] btrfs: fix rw device counting in __btrfs_free_extra_devids
dsterba at suse.cz
Wed Jul 28 12:58:05 UTC 2021
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:
> device_list_add(); <---------------- device added
> btrfs_open_one_device(); <-------- writable device opened,
> rw device count ++
> __btrfs_free_extra_devids(); <--- writable device removed,
> rw device count not decremented
> 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 at syzkaller.appspotmail.com
> Tested-by: syzbot+a70e2ad0879f160b9217 at syzkaller.appspotmail.com
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx at gmail.com>
> Reviewed-by: Anand Jain <anand.jain at oracle.com>
Added to misc-next, thanks.
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