linux-kernel - Re: [PATCH 1/1] block: System crashes when cpu hotplug + bouncing port

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Message-ID: <20210629083549.unco3f7atybqypw3@beryllium.lan>
Date:   Tue, 29 Jun 2021 10:35:49 +0200
From:   Daniel Wagner <dwagner@...e.de>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Wen Xiong <wenxiong@...ibm.com>, james.smart@...adcom.com,
        linux-kernel@...r.kernel.org, sagi@...mberg.me,
        wenxiong@...ux.vnet.ibm.com
Subject: Re: [PATCH 1/1] block: System crashes when cpu hotplug + bouncing
 port

On Tue, Jun 29, 2021 at 10:25:43AM +0200, Daniel Wagner wrote:
> On Tue, Jun 29, 2021 at 11:47:55AM +0800, Ming Lei wrote:
> > >    >>data.ctx = __blk_mq_get_ctx(q, cpu);
> > >    cpu=2048 if hctx_idx = 4
> > 
> > Yeah, that is the issue I mentioned, any CPU in hctx->cpumask becomes
> > offline, please try the following patch and see if it makes a
> > difference:
> 
> Given that cpumask_first_and() will return nr_cpu_ids in this case,
> can't we just bail out here and have to caller handle the error?

To answer my own question, you want to avoid adding the if into the
hotpath.