Re: [PATCH] Btrfs: fix racy system chunk allocation when setting block group ro

[Filipe David Manana <fdmanana@gmail.com>]

On Tue, May 19, 2015 at 12:32 PM, Holger Hoffstätte
<holger.hoffstaette@googlemail.com> wrote:
> On Mon, 18 May 2015 19:11:40 +0100, Filipe Manana wrote:
>
>> If while setting a block group read-only we end up allocating a system
>> chunk, through check_system_chunk(), we were not doing it while holding
>> the chunk mutex which is a problem if a concurrent chunk allocation is
>> happening, through do_chunk_alloc(), as it means both block groups can
>> end up using the same logical addresses and physical regions in the
>> device(s). So make sure we hold the chunk mutex.
>>
>> Cc: stable@vger.kernel.org  # 4.0+
>> Fixes: 2f0810880f08 ("btrfs: delete chunk allocation attemp when
>>                       setting block group ro")
>
> Hello Filipe,
>
> good find, as usual. But from the description it's not clear to me whether
> this also fixes rebalance seemingly not having an effect (as reported many
> times now) or "just" the on-disk block data getting munched together on a
> racy day? Just thought I'd ask for clarification before I start patching.

No, it doesn't fix the balance/conversion issue. It's a completely
separate issue/regression. Chris is working on the balance/conversion
issue.

thanks

>
> Thanks!
>
> Holger
>
>
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-- 
Filipe David Manana,

"Reasonable men adapt themselves to the world.
 Unreasonable men adapt the world to themselves.
 That's why all progress depends on unreasonable men."