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From: Joel Fernandes <joelagnelf@nvidia.com>
To: Peter Zijlstra <peterz@infradead.org>, Lyude Paul <lyude@redhat.com>
Cc: rust-for-linux@vger.kernel.org,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Boqun Feng" <boqun.feng@gmail.com>,
	linux-kernel@vger.kernel.org,
	"Daniel Almeida" <daniel.almeida@collabora.com>,
	"Danilo Krummrich" <dakr@kernel.org>,
	"Lorenzo Stoakes" <lorenzo.stoakes@oracle.com>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	"Liam R. Howlett" <Liam.Howlett@oracle.com>,
	"Uladzislau Rezki" <urezki@gmail.com>,
	"Miguel Ojeda" <ojeda@kernel.org>,
	"Alex Gaynor" <alex.gaynor@gmail.com>,
	"Gary Guo" <gary@garyguo.net>,
	"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
	"Benno Lossin" <lossin@kernel.org>,
	"Andreas Hindborg" <a.hindborg@kernel.org>,
	"Alice Ryhl" <aliceryhl@google.com>,
	"Trevor Gross" <tmgross@umich.edu>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	"Viresh Kumar" <viresh.kumar@linaro.org>,
	"Sebastian Andrzej Siewior" <bigeasy@linutronix.de>,
	"Ingo Molnar" <mingo@kernel.org>,
	"Ryo Takakura" <ryotkkr98@gmail.com>,
	"K Prateek Nayak" <kprateek.nayak@amd.com>,
	"open list:CPU FREQUENCY SCALING FRAMEWORK"
	<linux-pm@vger.kernel.org>
Subject: Re: [PATCH v13 01/17] preempt: Track NMI nesting to separate per-CPU counter
Date: Tue, 14 Oct 2025 13:55:47 -0400	[thread overview]
Message-ID: <4a237ec0-05ae-439b-a1cb-6b7f451c0d7e@nvidia.com> (raw)
In-Reply-To: <20251014104839.GN4067720@noisy.programming.kicks-ass.net>



On 10/14/2025 6:48 AM, Peter Zijlstra wrote:
> On Mon, Oct 13, 2025 at 11:48:03AM -0400, Lyude Paul wrote:
> 
>>  #define __nmi_enter()						\
>>  	do {							\
>>  		lockdep_off();					\
>>  		arch_nmi_enter();				\
>> -		BUG_ON(in_nmi() == NMI_MASK);			\
>> -		__preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET);	\
>> +		BUG_ON(__this_cpu_read(nmi_nesting) == UINT_MAX);	\
>> +		__this_cpu_inc(nmi_nesting);			\
> 
> An NMI that nests from here..
> 
>> +		__preempt_count_add(HARDIRQ_OFFSET);		\
>> +		if (__this_cpu_read(nmi_nesting) == 1)		\
> 
> .. until here, will see nmi_nesting > 1 and not set NMI_OFFSET.

This is true, I can cure it by setting NMI_OFFSET unconditionally when
nmi_nesting >= 1. Then the outer most NMI will then reset it. I think that will
work. Do you see any other issue with doing so?

Thanks!

 - Joel





  reply	other threads:[~2025-10-14 17:55 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20251013155205.2004838-1-lyude@redhat.com>
2025-10-13 15:48 ` [PATCH v13 01/17] preempt: Track NMI nesting to separate per-CPU counter Lyude Paul
2025-10-13 16:19   ` Lyude Paul
2025-10-13 16:32     ` Miguel Ojeda
2025-10-13 20:00   ` Peter Zijlstra
2025-10-13 21:27     ` Joel Fernandes
2025-10-14  8:25       ` Peter Zijlstra
2025-10-14 17:59         ` Joel Fernandes
2025-10-14 19:37           ` Peter Zijlstra
2025-10-14 10:48   ` Peter Zijlstra
2025-10-14 17:55     ` Joel Fernandes [this message]
2025-10-14 19:43       ` Peter Zijlstra
2025-10-14 22:05         ` Joel Fernandes
2025-10-20 20:44         ` Joel Fernandes
2025-10-30 22:56           ` Joel Fernandes

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