linux-kernel - Re: [PATCH v5 2/2] block: cancel all throttled bios in del

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Message-ID: <20220107150519.GA26824@blackbody.suse.cz>
Date:   Fri, 7 Jan 2022 16:05:19 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     tj@...nel.org, hch@...radead.org, axboe@...nel.dk,
        cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com
Subject: Re: [PATCH v5 2/2] block: cancel all throttled bios in del_gendisk()

On Fri, Dec 10, 2021 at 04:31:43PM +0800, Yu Kuai <yukuai3@...wei.com> wrote:
> +	 * queue_lock is held, rcu lock is not needed here.
> +	 */
> +	blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg)
> +		tg_drain_bios(&blkg_to_tg(blkg)->service_queue);

FTR, I acknowledge this can work due to RCU peculiarities, however, I
don't understand why is it preferred against more robust explict
rcu_read_lock().

(All in all, this isn't a deal breaker and I'm not confident evaluating
the rest of the patch.)

Michal