linux-kernel - Re: [PATCH 2/2] blk-mq: don't use WORK_CPU

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Message-ID: <20170821144855.GF491396@devbig577.frc2.facebook.com>
Date:   Mon, 21 Aug 2017 07:48:56 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Laurent Vivier <lvivier@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 2/2] blk-mq: don't use WORK_CPU_UNBOUND

On Mon, Aug 21, 2017 at 03:49:51PM +0200, Laurent Vivier wrote:
> cpumask is the list of CPUs present when the queue is built.
> If a new CPU is hotplugged, this list is not updated,
> and when the scheduler asks for a CPU id, blk_mq_hctx_next_cpu()
> can return WORK_CPU_UNBOUND.
> And in this case _blk_mq_run_hw_queue() can be executed by the new CPU
> (that is not present in cpumask) and raises the following warning:
> 
>     WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask) &&
>             cpu_online(hctx->next_cpu));
> 
> To fix this problem, this patch modifies blk_mq_hctx_next_cpu()
> to only return a CPU id present in cpumask.

So, this one isn't needed either.

Thanks.

-- 
tejun