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Message-ID: <20210820105828.GN5047@twin.jikos.cz>
Date: Fri, 20 Aug 2021 12:58:28 +0200
From: David Sterba <dsterba@...e.cz>
To: Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
Cc: dsterba@...e.cz, clm@...com, josef@...icpanda.com,
dsterba@...e.com, anand.jain@...cle.com,
linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
skhan@...uxfoundation.org, gregkh@...uxfoundation.org,
linux-kernel-mentees@...ts.linuxfoundation.org,
syzbot+a70e2ad0879f160b9217@...kaller.appspotmail.com
Subject: Re: [PATCH v2] btrfs: fix rw device counting in
__btrfs_free_extra_devids
On Fri, Aug 20, 2021 at 11:09:05AM +0800, Desmond Cheong Zhi Xi wrote:
> On 20/8/21 1:34 am, David Sterba wrote:
> > On Fri, Aug 20, 2021 at 01:11:58AM +0800, Desmond Cheong Zhi Xi wrote:
> >>>>> The option #2 does not sound safe because the TGT bit is checked in
> >>>>> several places where device list is queried for various reasons, even
> >>>>> without a mounted filesystem.
> >>>>>
> >>>>> Removing the assertion makes more sense but I'm still not convinced that
> >>>>> the this is expected/allowed state of a closed device.
> >>>>>
> >>>>
> >>>> Would it be better if we cleared the REPLACE_TGT bit only when closing
> >>>> the device where device->devid == BTRFS_DEV_REPLACE_DEVID?
> >>>>
> >>>> The first conditional in btrfs_close_one_device assumes that we can come
> >>>> across such a device. If we come across it, we should properly reset it.
> >>>>
> >>>> If other devices has this bit set, the ASSERT will still catch it and
> >>>> let us know something is wrong.
> >>>
> >>> That sounds great.
> >>>
> >>>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> >>>> index 70f94b75f25a..a5afebb78ecf 100644
> >>>> --- a/fs/btrfs/volumes.c
> >>>> +++ b/fs/btrfs/volumes.c
> >>>> @@ -1130,6 +1130,9 @@ static void btrfs_close_one_device(struct btrfs_device *device)
> >>>> fs_devices->rw_devices--;
> >>>> }
> >>>>
> >>>> + if (device->devid == BTRFS_DEV_REPLACE_DEVID)
> >>>> + clear_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state);
> >>>> +
> >>>> if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state))
> >>>> fs_devices->missing_devices--;
> >>>
> >>> I'll do a few test rounds, thanks.
> >>
> >> Just following up. Did that resolve the issue or is further
> >> investigation needed?
> >
> > The fix seems to work, I haven't seen the assertion fail anymore,
> > incidentally the crash also stopped to show up on an unpatched branch.
> >
>
> Sounds good, thanks for the update. If there's anything else I can help
> with, please let me know.
So are you going to send the patch with the fix?
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