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Date:   Thu, 25 Mar 2021 13:08:02 +0100
From:   David Sterba <dsterba@suse.cz>
To:     Sasha Levin <sashal@kernel.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Qu Wenruo <wqu@suse.com>, David Sterba <dsterba@suse.com>,
        linux-btrfs@vger.kernel.org
Subject: Re: [PATCH AUTOSEL 5.11 26/44] btrfs: track qgroup released data in
 own variable in insert_prealloc_file_extent
Message-ID: <20210325120802.GK7604@twin.jikos.cz>
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        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Qu Wenruo <wqu@suse.com>, David Sterba <dsterba@suse.com>,
        linux-btrfs@vger.kernel.org
References: <20210325112459.1926846-1-sashal@kernel.org>
 <20210325112459.1926846-26-sashal@kernel.org>
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On Thu, Mar 25, 2021 at 07:24:41AM -0400, Sasha Levin wrote:
> From: Qu Wenruo <wqu@suse.com>
> 
> [ Upstream commit fbf48bb0b197e6894a04c714728c952af7153bf3 ]
> 
> There is a piece of weird code in insert_prealloc_file_extent(), which
> looks like:
> 
> 	ret = btrfs_qgroup_release_data(inode, file_offset, len);
> 	if (ret < 0)
> 		return ERR_PTR(ret);
> 	if (trans) {
> 		ret = insert_reserved_file_extent(trans, inode,
> 						  file_offset, &stack_fi,
> 						  true, ret);
> 	...
> 	}
> 	extent_info.is_new_extent = true;
> 	extent_info.qgroup_reserved = ret;
> 	...
> 
> Note how the variable @ret is abused here, and if anyone is adding code
> just after btrfs_qgroup_release_data() call, it's super easy to
> overwrite the @ret and cause tons of qgroup related bugs.
> 
> Fix such abuse by introducing new variable @qgroup_released, so that we
> won't reuse the existing variable @ret.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> Reviewed-by: David Sterba <dsterba@suse.com>
> Signed-off-by: David Sterba <dsterba@suse.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>

This patch is a preparatory work and does not make sense for backport
standalone. Either this one plus
https://lore.kernel.org/linux-btrfs/20210303104152.105877-2-wqu@suse.com/
or neither. And IIRC it does not apply directly and needs some
additional review before it can be backported to older code base, so it
has no CC: stable tags.