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From:   Thomas Gleixner <tglx@linutronix.de>
To:     David Woodhouse <dwmw2@infradead.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        Waiman Long <longman@redhat.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        linux-kernel <linux-kernel@vger.kernel.org>
Cc:     Juergen Gross <jgross@suse.com>
Subject: Re: [PATCH] lockdep: add lockdep_cleanup_dead_cpu()
In-Reply-To: <e5ba02138c31da60daf91ce505ac3860d022332b.camel@infradead.org>
References: <e5ba02138c31da60daf91ce505ac3860d022332b.camel@infradead.org>
Date:   Sat, 28 Oct 2023 16:13:24 +0200
Message-ID: <877cn625tn.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
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On Sat, Oct 28 2023 at 12:14, David Woodhouse wrote:

> From: David Woodhouse <dwmw@amazon.co.uk>
>
> Add a function to check that an offlone CPU left the tracing infrastructure
> in a sane state. The acpi_idle_play_dead() function was recently observed
> calling safe_halt() instead of raw_safe_halt(), which had the side-effect
> of setting the hardirqs_enabled flag for the offline CPU. On x86 this
> triggered lockdep warnings when the CPU came back online, but too early
> for the exception to be handled correctly, leading to a triple-fault.
>
> Add lockdep_cleanup_dead_cpu() to check for this kind of failure mode,
> print the events leading up to it, and correct it so that the CPU can
> come online again correctly.
>
> [   61.556652] smpboot: CPU 1 is now offline
> [   61.556769] CPU 1 left hardirqs enabled!
> [   61.556915] irq event stamp: 128149
> [   61.556965] hardirqs last  enabled at (128149): [<ffffffff81720a36>] acpi_idle_play_dead+0x46/0x70
> [   61.557055] hardirqs last disabled at (128148): [<ffffffff81124d50>] do_idle+0x90/0xe0
> [   61.557117] softirqs last  enabled at (128078): [<ffffffff81cec74c>] __do_softirq+0x31c/0x423
> [   61.557199] softirqs last disabled at (128065): [<ffffffff810baae1>] __irq_exit_rcu+0x91/0x100
>
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>