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

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Message-ID: <87o819glbf.ffs@tglx>
Date:   Sun, 10 Apr 2022 14:44:04 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Christoph Hellwig <hch@...radead.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Christoph Hellwig <hch@...radead.org>,
        linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        Peter Zijlstra <peterz@...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 Thu, Feb 10 2022 at 22:34, Christoph Hellwig wrote:
> On Thu, Feb 10, 2022 at 01:33:39PM +0100, Sebastian Andrzej Siewior wrote:
>> You need to handle the pending softirqs. If you don't handle them
>> immediately or in a deterministic say (like on IRQ exit) then they will
>> be handled at a random point.
>
> Yes.  Just like regular interrupts.

But interrupts make sure they are handled. This code does not and as
Sebastian pointed out:

  "If you don't handle them at all, the CPU will go idle and at least
   the NO_HZ will complain about pending softirqs (can_stop_idle_tick())."

That's clearly a bug, but this should be part of the changelog.

Thanks,

        tglx