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([2603:8080:7400:36da:dff5:4180:2562:4c1e]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-7308b0077fdsm373355a34.0.2025.04.29.10.02.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 29 Apr 2025 10:02:14 -0700 (PDT) Message-ID: <781ef1d7-f9c6-4a15-b94d-c735e83e7d01@gmail.com> Date: Tue, 29 Apr 2025 10:25:04 -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 2/2] x86/panic: Add x86_panic_handler as default post-panic behavior To: John Ogness , carlos.bilbao@kernel.org, tglx@linutronix.de, seanjc@google.com, jan.glauber@gmail.com Cc: bilbao@vt.edu, pmladek@suse.com, akpm@linux-foundation.org, jani.nikula@intel.com, linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org, takakura@valinux.co.jp References: <20250428215952.1332985-1-carlos.bilbao@kernel.org> <20250428215952.1332985-3-carlos.bilbao@kernel.org> <84ldri7vv0.fsf@jogness.linutronix.de> Content-Language: en-US From: Carlos Bilbao In-Reply-To: <84ldri7vv0.fsf@jogness.linutronix.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hello John, On 4/29/25 11:53, John Ogness wrote: > On 2025-04-28, carlos.bilbao@kernel.org wrote: >> From: Carlos Bilbao >> >> Add function x86_panic_handler() as the default behavior for x86 for >> post-panic stage via panic_set_handling(). Instead of busy-wait loop, it >> will halt if there's no console to save CPU cycles. >> >> Signed-off-by: Carlos Bilbao (DigitalOcean) >> --- >> arch/x86/kernel/setup.c | 12 ++++++++++++ >> 1 file changed, 12 insertions(+) >> >> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c >> index 9d2a13b37833..3bfef55e9adb 100644 >> --- a/arch/x86/kernel/setup.c >> +++ b/arch/x86/kernel/setup.c >> @@ -16,6 +16,7 @@ >> #include >> #include >> #include >> +#include >> #include >> #include >> #include >> @@ -837,6 +838,15 @@ static void __init x86_report_nx(void) >> } >> } >> >> + >> +static void x86_panic_handler(void) >> +{ >> + if (console_trylock()) { >> + console_unlock(); >> + safe_halt(); >> + } > I do not understand what you are trying to accomplish with the > console_trylock(). At this point in the panic, all the messages are > already output. The console lock is totally irrelevant. > > Also, the console lock is only valid for legacy consoles. > > I see no reason why you don't just use safe_halt() as your panic > handler. Yes, in my original implementation I simply used halt, but I was trying to be cautious in case any remaining messages hadn't flushed. I wonder, can we be certain that, as you said, all output (e.g., a backtrace) has already been displayed on screen at this point? I'm not sure. > > John Ogness Thanks, Carlos