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Message-ID: <8f3765db-842d-4568-9ac5-1bd9cab9e952@web.de>
Date: Fri, 5 Jul 2024 19:05:39 +0200
From: Markus Elfring <Markus.Elfring@....de>
To: Boy Wu <boy.wu@...iatek.com>, cgroups@...r.kernel.org,
linux-block@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-mediatek@...ts.infradead.org, Jens Axboe <axboe@...nel.dk>,
Josef Bacik <josef@...icpanda.com>, Tejun Heo <tj@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Angelo Gioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
Boris Burkov <boris@....io>, Iverlin Wang (王苳霖)
<Iverlin.Wang@...iatek.com>, Matthias Brugger <matthias.bgg@...il.com>
Subject: Re: [PATCH] blk-cgroup: add spin_lock for u64_stats_update
> In 32bit SMP systems, if the system is stressed on the sys node
> by processes, it may cause blkcg_fill_root_iostats to have a concurrent
> problem on the seqlock in u64_stats_update, which will cause a deadlock
> on u64_stats_fetch_begin in blkcg_print_one_stat.
Would you like to mark any references to functions with parentheses?
> To prevent this problem, add spin_locks.
Another wording suggestion:
Thus use an additional spin lock.
How do you think about to use a summary phrase like “Add a spin lock for stats update
in blkcg_fill_root_iostats()”?
…
> +++ b/block/blk-cgroup.c
> @@ -1134,9 +1134,15 @@ static void blkcg_fill_root_iostats(void)
> cpu_dkstats->sectors[STAT_DISCARD] << 9;
> }
>
> +#if BITS_PER_LONG == 32
> + spin_lock_irq(&blkg->q->queue_lock);
> +#endif
> flags = u64_stats_update_begin_irqsave(&blkg->iostat.sync);
> blkg_iostat_set(&blkg->iostat.cur, &tmp);
> u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags);
> +#if BITS_PER_LONG == 32
> + spin_unlock_irq(&blkg->q->queue_lock);
> +#endif
…
Under which circumstances would you become interested to apply a statement
like “guard(spinlock_irq)(&blkg->q->queue_lock);”?
https://elixir.bootlin.com/linux/v6.10-rc6/source/include/linux/spinlock.h#L567
Regards,
Markus
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