linux-kernel - Re: 'perf test sigtrap' failing on PREEMPT_RT

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Date:   Fri, 28 Jul 2023 17:07:18 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Mike Galbraith <efault@....de>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Marco Elver <elver@...gle.com>, linux-rt-users@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Clark Williams <williams@...hat.com>,
        ThomasGleixner <tglx@...utronix.de>
Subject: Re: 'perf test sigtrap' failing on PREEMPT_RT_FULL

On 2023-07-26 08:10:45 [+0200], Mike Galbraith wrote:
> > [   52.848925] BUG: scheduling while atomic: perf/6549/0x00000002
> 
> Had bf9ad37dc8a not been reverted due to insufficient beauty, you could
> trivially make the sigtrap test a happy camper (wart tested in tip-rt).

Thank you for the pointer Mike.

I guess we need this preempt_disable_notrace() in perf_pending_task()
due to context accounting in get_recursion_context(). Would a
migrate_disable() be sufficient or could we send the signal outside of
the preempt-disabled block?

This is also used in perf_pending_irq() and on PREEMPT_RT this is
invoked from softirq context which is preemptible.

Sebastian