linux-kernel - [RFC] panic: redundant backtraces with SYS_INFO_ALL_CPU

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Message-ID: <wgczmfbmzppwqvdjvsmhwzravvfzkabgeh6yifc3y4syl76xy5@ytgnkkmmcpr7>
Date: Wed, 23 Jul 2025 17:47:36 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Petr Mladek <pmladek@...e.com>, 
	John Ogness <john.ogness@...utronix.de>, Steven Rostedt <rostedt@...dmis.org>, 
	Peter Zijlstra <peterz@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	linux-kernel@...r.kernel.org
Subject: [RFC] panic: redundant backtraces with SYS_INFO_ALL_CPU_BT

Hello folks,

Should SYS_INFO_ALL_CPU_BT use trigger_allbutcpu_cpu_backtrace(),
instead of trigger_all_cpu_backtrace(), to exclude self/panic-cpu?
Otherwise it dumps extra backtraces for the panic CPU, which is
a little redundant (and confusing.)

E.g.
softlockup watchdog_timer_fn() calls dump_stack() from IRQ for the
locked-up CPU before it calls into panic() (assuming soft lockup panic),
which then can SYS_INFO_ALL_CPU_BT and trigger NMI backtraces for all CPUs,
including panic CPU which already dumped its stack, but this time we
dump_stack() from NMI.

I suspect it's a similar story for BUG()/BUG_ON() (and WARN/WARN_ON(),
assuming panic on warn.)