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

["Holger Hoffstätte" <holger.hoffstaette@googlemail.com>]

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.

Thanks!

Holger