linux-kernel - Re: [PATCH v3 0/3] blk-mq: Don't complete in IRQ, use llist

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Date:   Sun, 24 Jan 2021 21:27:54 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v3 0/3] blk-mq: Don't complete in IRQ, use llist_head

On 1/23/21 1:10 PM, Sebastian Andrzej Siewior wrote:
> Patch 2+3 were applied and then dropped by Jens due to a NOHZ+softirq
> related warning [0]. Turns out a successful wakeup via
> set_nr_if_polling() will not process any softirqs and the CPU may go
> back to idle. This is addressed by patch #1.
> 
> smpcfd_dying_cpu() will also invoke SMP-functions calls via
> flush_smp_call_function_queue() but the block layer shouldn't queue
> anything because the CPU isn't online anymore.
> The two caller of flush_smp_call_function_from_idle() look fine with
> opening interrupts from within do_softirq().
> 
> [0] https://lkml.kernel.org/r/1ee4b31b-350e-a9f5-4349-cfb34b89829a@kernel.dk

I can queue up the block side once the IPI fix is in some stable branch
that I can pull in.

-- 
Jens Axboe