linux-ext4 - Re: [PATCH 4/4] ext4: avoid dividing by 0 in mb_update_avg_fragment

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Message-ID: <20231218150905.llu5tgjgen4nxthq@quack3>
Date: Mon, 18 Dec 2023 16:09:05 +0100
From: Jan Kara <jack@...e.cz>
To: Baokun Li <libaokun1@...wei.com>
Cc: linux-ext4@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca,
	jack@...e.cz, ritesh.list@...il.com, linux-kernel@...r.kernel.org,
	yi.zhang@...wei.com, yangerkun@...wei.com, yukuai3@...wei.com,
	stable@...r.kernel.org
Subject: Re: [PATCH 4/4] ext4: avoid dividing by 0 in
 mb_update_avg_fragment_size() when block bitmap corrupt

On Mon 18-12-23 15:43:42, Jan Kara wrote:
> On Mon 18-12-23 22:18:14, Baokun Li wrote:
> > When bb_free is not 0 but bb_fragments is 0, return directly to avoid
> > system crash due to division by zero.
> 
> How could this possibly happen? bb_fragments is the number of free space
> extents and bb_free is the number of free blocks. No free space extents =>
> no free blocks seems pretty obvious? You can see the logic in
> ext4_mb_generate_buddy()...

Oh, I see. This is probably about "bitmap corrupted case". But still both
allocation and freeing of blocks shouldn't operate on bitmaps marked as
corrupted so this should not happen?

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR