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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Wang Shuaiwei <wangshuaiwei1@xiaomi.com>
Cc: Frederic Weisbecker <frederic@kernel.org>,
	Thomas Gleixner <tglx@kernel.org>, Jens Axboe <axboe@kernel.dk>,
	wanghui33@xiaomi.com, linux-kernel@vger.kernel.org,
	linux-block@vger.kernel.org
Subject: Re: [PATCH] tick/block: Add BLOCK_SOFTIRQ to the hotplug safe mask
Message-ID: <20260917095110.Yxq3FCrB@linutronix.de>
References: <20260904064506.671203-1-wangshuaiwei1@xiaomi.com>
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In-Reply-To: <20260904064506.671203-1-wangshuaiwei1@xiaomi.com>

On 2026-09-04 14:45:06 [+0800], Wang Shuaiwei wrote:
> During CPU-hotplug stress testing combined with an I/O
> workload, the following message is observed:
> 
>   "NOHZ tick-stop error: local softirq work is pending, handler #10!!!"
> 
> On CPU offline, ksoftirqd is parked at CPUHP_AP_SMPBOOT_THREADS while
> the CPU still takes interrupts. A block completion raised after that
> point stays pending, and if the dying CPU goes idle before teardown,
> report_idle_softirq() sees it, keeps the tick alive and prints the
> error above.
> 
> Such pending block completions on the outgoing CPU are drained later by
> blk_softirq_cpu_dead() (CPUHP_BLOCK_SOFTIRQ_DEAD), so a pending
> BLOCK_SOFTIRQ is harmless here. Add it to SOFTIRQ_HOTPLUG_SAFE_MASK
> like the other teardown-covered vectors.
> 
> Signed-off-by: Wang Shuaiwei <wangshuaiwei1@xiaomi.com>

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Should this go via nohz, softirq or block?

Sebastian