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Tue, 23 Jun 2026 05:37:08 -0700 (PDT) Date: Tue, 23 Jun 2026 14:37:00 +0200 From: Petr Mladek To: Bradley Morgan Cc: Andrew Morton , Douglas Anderson , Mayank Rungta , Tejun Heo , Feng Tang , ZhenguoYao , Shengming Hu , Joel Granados , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] watchdog: avoid extra sys_info dumps for all_bt Message-ID: References: <20260620220140.15479-1-include@grrlz.net> Precedence: bulk X-Mailing-List: linux-kernel@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: <20260620220140.15479-1-include@grrlz.net> On Sat 2026-06-20 22:01:40, Bradley Morgan wrote: > The watchdog handles SYS_INFO_ALL_BT itself. When that is the only > watchdog specific bit, sys_info(0) falls back to kernel_sys_info. Great catch! > Skip sys_info() for that case. > > Fixes: a9af76a78760 ("watchdog: add sys_info sysctls to dump sys info on system lockup") > Signed-off-by: Bradley Morgan > --- a/kernel/watchdog.c > +++ b/kernel/watchdog.c > @@ -54,6 +54,16 @@ static int __read_mostly watchdog_hardlockup_available; > struct cpumask watchdog_cpumask __read_mostly; > unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask); > Similar problem exists also in kernel/panic.c. It would make sense to put this variant into lib/sys_info.c and use a generic name, e.g. sys_info_without_all_bt(). > +static void watchdog_sys_info(unsigned long si_mask) > +{ > + unsigned long dump_mask = si_mask & ~SYS_INFO_ALL_BT; > + This looks like an optimization. The real reason is not obvious. It would deserve a comment, something like: /* * Do not call sys_info() when the caller context required * only backtraces from all CPUs. Otherwise, sys_info() * would fall back to the generic "kernel_si_mask". */ > + if (si_mask && !dump_mask) > + return; > + > + sys_info(dump_mask); > +} Alternative solution would be to remove the custom trigger_all*_cpu_backtrace() calls from both watchdog and panic code and rely on sys_info() API. But it is not easy, especially in panic(). Otherwise, the changes make sense. Best Regards, Petr