Messages in this thread Patch in this message | | | From | Desmond Cheong Zhi Xi <> | Subject | [PATCH v2] btrfs: fix rw device counting in __btrfs_free_extra_devids | Date | Tue, 27 Jul 2021 15:13:03 +0800 |
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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> --- fs/btrfs/volumes.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 807502cd6510..916c25371658 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -1078,6 +1078,7 @@ static void __btrfs_free_extra_devids(struct btrfs_fs_devices *fs_devices, if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) { list_del_init(&device->dev_alloc_list); clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state); + fs_devices->rw_devices--; } list_del_init(&device->dev_list); fs_devices->num_devices--; -- 2.25.1
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