From: Peter Zijlstra <peterz@infradead•org>
To: Douglas Anderson <dianders@chromium•org>
Cc: linux-mips@linux-mips•org,
Daniel Thompson <daniel.thompson@linaro•org>,
linux-sh@vger•kernel.org, gregkh@linuxfoundation•org,
frederic@kernel•org, Jason Wessel <jason.wessel@windriver•com>,
linux-kernel@vger•kernel.org, sparclinux@vger•kernel.org,
linux-arm-kernel@lists•infradead.org, luto@kernel•org,
linux-arm-msm@vger•kernel.org,
kgdb-bugreport@lists•sourceforge.net,
linux-hexagon@vger•kernel.org, tglx@linutronix•de,
linux-snps-arc@lists•infradead.org,
linuxppc-dev@lists•ozlabs.org, mingo@kernel•org,
riel@surriel•com
Subject: Re: [PATCH 6/7] smp: Don't yell about IRQs disabled in kgdb_roundup_cpus()
Date: Tue, 30 Oct 2018 09:25:25 +0100 [thread overview]
Message-ID: <20181030082525.GA13436@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20181029180707.207546-7-dianders@chromium.org>
On Mon, Oct 29, 2018 at 11:07:06AM -0700, Douglas Anderson wrote:
> In kgdb_roundup_cpus() we've got code that looks like:
> local_irq_enable();
> smp_call_function(kgdb_call_nmi_hook, NULL, 0);
> local_irq_disable();
> Let's add kgdb to the list of reasons not to warn in
> smp_call_function_many(). That will allow us (in a future patch) to
> stop calling local_irq_enable() which will get rid of the original
> splat.
>
> NOTE: with this change comes the obvious question: will we start
> deadlocking more often now when we drop into the debugger. I can't
> say that for sure one way or the other, but the fact that we do the
> same logic for "oops_in_progress" makes me feel like it shouldn't
> happen too often. Also note that the old logic of turning on
> interrupts temporarily wasn't exactly safe since (I presume) that
> could have violated spin_lock_irqsave() semantics and ended up with a
> deadlock of its own.
How is any of that not utterly and terminally broken?
> @@ -413,7 +414,8 @@ void smp_call_function_many(const struct cpumask *mask,
> * can't happen.
> */
> WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
> - && !oops_in_progress && !early_boot_irqs_disabled);
> + && !oops_in_progress && !early_boot_irqs_disabled
> + && !in_dbg_master());
>
> /* Try to fastpath. So, what's a CPU they want? Ignoring this one. */
> cpu = cpumask_first_and(mask, cpu_online_mask);
Not a fan of this. There is a distinct difference between
oops_in_progress and dropping into kgdb in that you don't ever expect to
return/survive oopses, whereas we do expect to survive kgdb.
Also, how does kgdb work at all without actual NMIs ?
So no, NAK on this.
next prev parent reply other threads:[~2018-10-30 15:57 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-29 18:07 [PATCH 0/7] serial: Finish kgdb on qcom_geni; fix many lockdep splats w/ kgdb Douglas Anderson
2018-10-29 18:07 ` [PATCH 6/7] smp: Don't yell about IRQs disabled in kgdb_roundup_cpus() Douglas Anderson
2018-10-30 8:25 ` Peter Zijlstra [this message]
2018-10-30 9:41 ` Daniel Thompson
2018-10-30 22:21 ` Doug Anderson
2018-10-29 18:07 ` [PATCH 7/7] kgdb: Remove irq flags and local_irq_enable/disable from roundup Douglas Anderson
2018-10-30 11:46 ` Daniel Thompson
2018-10-30 22:22 ` Doug Anderson
2018-10-30 11:56 ` [PATCH 0/7] serial: Finish kgdb on qcom_geni; fix many lockdep splats w/ kgdb Daniel Thompson
2018-10-30 12:31 ` Russell King - ARM Linux
2018-10-30 22:20 ` Doug Anderson
2018-10-30 12:36 ` Andy Shevchenko
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