linux-kernel - Re: [PATCH AUTOSEL 4.19 34/38] btrfs: file: reserve qgroup space after the hole punch range is locked

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Message-ID: <20200829121123.GB20944@duo.ucw.cz>
Date:   Sat, 29 Aug 2020 14:11:23 +0200
From:   Pavel Machek <pavel@....cz>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Qu Wenruo <wqu@...e.com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 4.19 34/38] btrfs: file: reserve qgroup space
 after the hole punch range is locked

Hi!

> [ Upstream commit a7f8b1c2ac21bf081b41264c9cfd6260dffa6246 ]
> 
> The incoming qgroup reserved space timing will move the data reservation
> to ordered extent completely.
> 
> However in btrfs_punch_hole_lock_range() will call
> btrfs_invalidate_page(), which will clear QGROUP_RESERVED bit for the
> range.
> 
> In current stage it's OK, but if we're making ordered extents handle the
> reserved space, then btrfs_punch_hole_lock_range() can clear the
> QGROUP_RESERVED bit before we submit ordered extent, leading to qgroup
> reserved space leakage.
> 
> So here change the timing to make reserve data space after
> btrfs_punch_hole_lock_range().
> The new timing is fine for either current code or the new code.

I'm not sure why this is queued for -stable. It is preparation for
future work, and that work is not queued for -stable.

Best regards,
							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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