linux-kernel - Re: [PATCH v4 3/3] block: prevent race condition on bi_status in __bio_chain

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aS17LOwklgbzNhJY@infradead.org>
Date: Mon, 1 Dec 2025 03:25:32 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Andreas Gruenbacher <agruenba@...hat.com>
Cc: zhangshida <starzhangzsd@...il.com>, Johannes.Thumshirn@....com,
	hch@...radead.org, ming.lei@...hat.com, hsiangkao@...ux.alibaba.com,
	csander@...estorage.com, colyli@...as.com,
	linux-block@...r.kernel.org, linux-bcache@...r.kernel.org,
	linux-kernel@...r.kernel.org, zhangshida@...inos.cn,
	Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v4 3/3] block: prevent race condition on bi_status in
 __bio_chain_endio

On Mon, Dec 01, 2025 at 11:22:32AM +0100, Andreas Gruenbacher wrote:
> > -       if (bio->bi_status && !parent->bi_status)
> > -               parent->bi_status = bio->bi_status;
> > +       if (bio->bi_status)
> > +               cmpxchg(&parent->bi_status, 0, bio->bi_status);
> 
> Hmm. I don't think cmpxchg() actually is of any value here: for all
> the chained bios, bi_status is initialized to 0, and it is only set
> again (to a non-0 value) when a failure occurs. When there are
> multiple failures, we only need to make sure that one of those
> failures is eventually reported, but for that, a simple assignment is
> enough here.

A simple assignment doesn't guarantee atomicy.  It also overrides
earlier with later status codes, which might not be desirable.