linux-kernel - Re: [PATCH] blk-cgroup: add spin_lock for u64_stats

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Message-ID: <Zogpum23mjHZC8yO@slm.duckdns.org>
Date: Fri, 5 Jul 2024 07:13:30 -1000
From: Tejun Heo <tj@...nel.org>
To: "boy.wu" <boy.wu@...iatek.com>
Cc: Josef Bacik <josef@...icpanda.com>, Jens Axboe <axboe@...nel.dk>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Boris Burkov <boris@....io>, cgroups@...r.kernel.org,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org, iverlin.wang@...iatek.com
Subject: Re: [PATCH] blk-cgroup: add spin_lock for u64_stats_update

Hello,

On Fri, Jul 05, 2024 at 03:55:44PM +0800, boy.wu wrote:
> From: Boy Wu <boy.wu@...iatek.com>
> 
> 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

What is sys node?

> problem on the seqlock in u64_stats_update, which will cause a deadlock 
> on u64_stats_fetch_begin in blkcg_print_one_stat.

I'm not following the scenario. Can you please detail the scenario where
this leads to deadlocks?

Thanks.

-- 
tejun