linux-kernel - Re: [PATCH REPOST] irq_poll: Add local_bh_disable() in cpu

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Date:   Tue, 8 Feb 2022 23:56:34 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoph Hellwig <hch@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH REPOST] irq_poll: Add local_bh_disable() in cpu_dead
 notifier

On Tue, Feb 08, 2022 at 03:34:05PM +0100, Sebastian Andrzej Siewior wrote:
> __raise_softirq_irqoff() adds a bit to the pending sofirq mask and this
> is it. The softirq won't be handled in a deterministic way but randomly
> when an interrupt fires and handles the softirq in its irq_exit() routine or
> if something randomly checks and handles pending softirqs in the call
> chain before the CPU goes idle.
> 
> Add a local_bh_disable/enable() around the IRQ-off section which will
> handle pending softirqs.

And I still haven't seen any good explanation of why this is useful.