Messages in this thread | | | Subject | Re: [PATCH] btrfs: fix rw device counting in __btrfs_free_extra_devids | From | Desmond Cheong Zhi Xi <> | Date | Thu, 15 Jul 2021 21:11:43 +0800 |
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On 15/7/21 7:55 pm, Nikolay Borisov wrote: > > > On 15.07.21 г. 13:34, Desmond Cheong Zhi Xi wrote: >> Syzbot reports a warning in close_fs_devices that happens because >> fs_devices->rw_devices is not 0 after calling btrfs_close_one_device >> on each device. >> >> This happens when a writeable device is removed in >> __btrfs_free_extra_devids, but the rw device count is not decremented >> accordingly. So when close_fs_devices is called, the removed device is >> still counted and we get an off by 1 error. >> >> Here is one 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(); <-------- rw device count ++ >> btrfs_fill_super(): >> open_ctree(): >> btrfs_free_extra_devids(): >> __btrfs_free_extra_devids(); <--- device removed >> fail_tree_roots: >> btrfs_close_devices(): >> close_fs_devices(); <------- rw device count off by 1 >> >> 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> > > Is there a reliable reproducer from syzbot? Can this be turned into an > xfstest? >
Syzbot has some reliable reproducers here: https://syzkaller.appspot.com/bug?id=113d9a01cbe0af3e291633ba7a7a3e983b86c3c0
Seems like it constructs two images in-memory then mounts them. I'm not sure if that's amenable to be converted into an xfstest?
>> --- >> 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--; >>
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