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([2601:188:ca00:a00:f844:fad5:7984:7bd7]) by smtp.gmail.com with ESMTPSA id 8926c6da1cb9f-4e230dded27sm3180285173.73.2024.12.04.11.28.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 04 Dec 2024 11:28:37 -0800 (PST) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <59b254dc-acf6-4114-b6b4-a7ae517bfa06@redhat.com> Date: Wed, 4 Dec 2024 14:28:35 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] x86/nmi: Add an emergency handler in nmi_desc & use it in nmi_shootdown_cpus() To: Thomas Gleixner , Waiman Long , Ingo Molnar , Borislav Petkov , Dave Hansen , Peter Zijlstra Cc: x86@kernel.org, linux-kernel@vger.kernel.org, "H. Peter Anvin" References: <20241203150732.182065-1-longman@redhat.com> <87h67jsif0.ffs@tglx> <7aa93137-4b5e-474f-a99c-47acffdf71a3@redhat.com> <87zflbqqar.ffs@tglx> Content-Language: en-US In-Reply-To: <87zflbqqar.ffs@tglx> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12/4/24 1:03 PM, Thomas Gleixner wrote: > On Wed, Dec 04 2024 at 12:23, Waiman Long wrote: >> On 12/4/24 8:10 AM, Thomas Gleixner wrote: >>> On Tue, Dec 03 2024 at 10:07, Waiman Long wrote: >>>> + /* >>>> + * Call the emergency handler first, if set >>>> + * Emergency handler is not traced or checked by nmi_check_duration(). >>>> + */ >>>> + ehandler = READ_ONCE(desc->emerg_handler); >>>> + if (ehandler) >>>> + handled = ehandler(type, regs); >>> Shouldn't this just stop processing right here? >> Yes in the case of crash_nmi_callback(). I suppose it is a no-return >> call. As the emergency handler is supposed to be a general mechanism in >> design, I don't want to make too many assumptions of what will happen >> when the handler is invoked. > I'm not convinced that this should be used as a general mechanism. It's > for emergency situations and that's where it stops. If the thing > returns, it's a bug IMO. OK, I am fine with that. I will put a BUG_ON() after that in the next version. Thanks, Longman