linux-kernel - Re: [PATCH 08/19] btrfs: make unmirroed BGs readonly only if we have at least one writable BG

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Message-ID: <20190618133516.giriyfzpnhdquuot@MacBook-Pro-91.local>
Date:   Tue, 18 Jun 2019 09:35:17 -0400
From:   Josef Bacik <josef@...icpanda.com>
To:     Naohiro Aota <Naohiro.Aota@....com>
Cc:     Josef Bacik <josef@...icpanda.com>,
        "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
        David Sterba <dsterba@...e.com>, Chris Mason <clm@...com>,
        Qu Wenruo <wqu@...e.com>, Nikolay Borisov <nborisov@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hannes Reinecke <hare@...e.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Matias Bjørling <mb@...htnvm.io>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Bart Van Assche <bvanassche@....org>
Subject: Re: [PATCH 08/19] btrfs: make unmirroed BGs readonly only if we have
 at least one writable BG

On Tue, Jun 18, 2019 at 07:42:46AM +0000, Naohiro Aota wrote:
> On 2019/06/13 23:09, Josef Bacik wrote:
> > On Fri, Jun 07, 2019 at 10:10:14PM +0900, Naohiro Aota wrote:
> >> If the btrfs volume has mirrored block groups, it unconditionally makes
> >> un-mirrored block groups read only. When we have mirrored block groups, but
> >> don't have writable block groups, this will drop all writable block groups.
> >> So, check if we have at least one writable mirrored block group before
> >> setting un-mirrored block groups read only.
> >>
> > 
> > I don't understand why you want this.  Thanks,
> > 
> > Josef
> > 
> 
> This is necessary to handle e.g. btrfs/124 case.
> 
> When we mount degraded RAID1 FS and write to it, and then
> re-mount with full device, the write pointers of corresponding
> zones of written BG differ.  The patch 07 mark such block group
> as "wp_broken" and make it read only.  In this situation, we only
> have read only RAID1 BGs because of "wp_broken" and un-mirrored BGs
> are also marked read only, because we have RAID1 BGs.
> As a result, all the BGs are now read only, so that we
> cannot even start the rebalance to fix the situation.

Ah ok, please add this explanation to the changelog.  Thanks,

Josef