Re: [Devel] [PATCH hci-8.1 v5 5/7] drivers/md/push_backup: arm deadline timer under pb->lock - no-reply

From: no-reply@sashiko.virtuozzo.com
To: khorenko@virtuozzo.com, alexander.ivanov@virtuozzo.com,
	Andrey Zhadchenko <andrey.zhadchenko@virtuozzo.com>
Cc: devel@openvz.org
Subject: Re: [Devel] [PATCH hci-8.1 v5 5/7] drivers/md/push_backup: arm deadline timer under pb->lock
Date: Tue, 3 Nov 2026 12:48:30 +0000	[thread overview]
Message-ID: <010701a1a174370e-6f9a8733-ddef-4388-87cb-6ae6953e04c2-000000@eu-central-1.amazonses.com> (raw)
In-Reply-To: <20261103123802.846676-6-andrey.zhadchenko@virtuozzo.com>

> Both pb_timer_func() and postpone_if_required_for_backup() decide
> whether to arm the timer under pb->lock but call mod_timer() after
> dropping it, so the decisions can be applied out of order:
> 
>   CPU1 pb_timer_func()            CPU2 postpone_if_required_for_backup()
>   lock; deadline = S64_MAX
>   unlock
>                                   lock; nr_delayed = 1
>                                   deadline_jiffies = now + timeout
>                                   unlock
>                                   mod_timer(timeout)
>   mod_timer(from S64_MAX)
> 
> The late mod_timer() of the callback overwrites the fresh deadline, and
> the write is delayed with the timer parked in a very distant future.
> [ ... ]
> pb->ctl_rwsem; the next patch removes that call.
> 
> Fixes: 62e07487348e ("dm: Add push backup driver")
> https://virtuozzo.atlassian.net/browse/VSTOR-152912
> Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko@virtuozzo.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.vzint.dev/#/patchset/20261103123802.846676-1-andrey.zhadchenko@virtuozzo.com?part=5

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