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[195.250.132.146]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46fb489ad27sm230711415e9.15.2025.10.14.02.45.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Oct 2025 02:45:07 -0700 (PDT) Date: Tue, 14 Oct 2025 11:45:05 +0200 From: Petr Mladek To: Lance Yang Cc: lirongqing , wireguard@lists.zx2c4.com, linux-arm-kernel@lists.infradead.org, "Liam R . Howlett" , linux-doc@vger.kernel.org, David Hildenbrand , Randy Dunlap , Stanislav Fomichev , linux-aspeed@lists.ozlabs.org, Andrew Jeffery , Joel Stanley , Russell King , Lorenzo Stoakes , Shuah Khan , Steven Rostedt , Jonathan Corbet , Joel Granados , Andrew Morton , Phil Auld , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Masami Hiramatsu , Jakub Kicinski , Pawan Gupta , Simon Horman , Anshuman Khandual , Florian Westphal , netdev@vger.kernel.org, Kees Cook , Arnd Bergmann , "Paul E . McKenney" , Feng Tang , "Jason A . Donenfeld" Subject: Re: [PATCH][v3] hung_task: Panic after fixed number of hung tasks Message-ID: References: <20251012115035.2169-1-lirongqing@baidu.com> <588c1935-835f-4cab-9679-f31c1e903a9a@linux.dev> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <588c1935-835f-4cab-9679-f31c1e903a9a@linux.dev> On Tue 2025-10-14 13:23:58, Lance Yang wrote: > Thanks for the patch! > > I noticed the implementation panics only when N tasks are detected > within a single scan, because total_hung_task is reset for each > check_hung_uninterruptible_tasks() run. Great catch! Does it make sense? Is is the intended behavior, please? > So some suggestions to align the documentation with the code's > behavior below :) > On 2025/10/12 19:50, lirongqing wrote: > > From: Li RongQing > > > > Currently, when 'hung_task_panic' is enabled, the kernel panics > > immediately upon detecting the first hung task. However, some hung > > tasks are transient and the system can recover, while others are > > persistent and may accumulate progressively. My understanding is that this patch wanted to do: + report even temporary stalls + panic only when the stall was much longer and likely persistent Which might make some sense. But the code does something else. > > --- a/kernel/hung_task.c > > +++ b/kernel/hung_task.c > > @@ -229,9 +232,11 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout) > > */ > > sysctl_hung_task_detect_count++; > > + total_hung_task = sysctl_hung_task_detect_count - prev_detect_count; > > trace_sched_process_hang(t); > > - if (sysctl_hung_task_panic) { > > + if (sysctl_hung_task_panic && > > + (total_hung_task >= sysctl_hung_task_panic)) { > > console_verbose(); > > hung_task_show_lock = true; > > hung_task_call_panic = true; I would expect that this patch added another counter, similar to sysctl_hung_task_detect_count. It would be incremented only once per check when a hung task was detected. And it would be cleared (reset) when no hung task was found. Best Regards, Petr