+ panic-avoid-the-extra-noise-dmesg.patch added to -mm tree

akpm
2018-12-04T07:15:37Z

The patch titled
Subject: panic: Avoid the extra noise dmesg
has been added to the -mm tree. Its filename is
panic-avoid-the-extra-noise-dmesg.patch

This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/panic-avoid-the-extra-noise-dmesg.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/panic-avoid-the-extra-noise-dmesg.patch

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------------------------------------------------------
From: Feng Tang <feng.tang@intel.com>
Subject: panic: Avoid the extra noise dmesg

When kernel panic happens, it will first print the panic call stack,
then the ending msg like:

[ 35.743249] ---[ end Kernel panic - not syncing: Fatal exception
[ 35.749975] ------------[ cut here ]------------

The above message are very useful for debugging.

But if system is configured to not reboot on panic, say the "panic_timeout"
parameter equals 0, it will likely print out many noisy message like
WARN() call stack for each and every CPU except the panic one, messages
like below:

WARNING: CPU: 1 PID: 280 at kernel/sched/core.c:1198 set_task_cpu+0x183/0x190
Call Trace:
<IRQ>
try_to_wake_up
default_wake_function
autoremove_wake_function
__wake_up_common
__wake_up_common_lock
__wake_up
wake_up_klogd_work_func
irq_work_run_list
irq_work_tick
update_process_times
tick_sched_timer
__hrtimer_run_queues
hrtimer_interrupt
smp_apic_timer_interrupt
apic_timer_interrupt

For people working in console mode, the screen will first show the panic
call stack, but immediately overridded by these noisy extra messages, which
makes debugging much more difficult, as the original context gets lost on
screen.

Also these noisy messages will confuse some users, as I have seen many bug
reporters posted the noisy message into bugzilla, instead of the real panic
call stack and context.

Removing the "local_irq_enable" will avoid the noisy message.

The justification for the removing is: when code runs to this point, it
means user has chosed to not reboot, or do any special handling by using
the panic notifier method, no much point in re-enabling the interrupt.

Link: http://lkml.kernel.org/r/1543902228-23834-1-git-send-email-feng.tang@intel.com
Signed-off-by: Feng Tang <feng.tang@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kees Cook <keescook@chromium.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

--- a/kernel/panic.c~panic-avoid-the-extra-noise-dmesg
+++ a/kernel/panic.c
@@ -322,7 +322,6 @@ void panic(const char *fmt, ...)
}
#endif
pr_emerg("---[ end Kernel panic - not syncing: %s ]---\n", buf);
- local_irq_enable();
for (i = 0; ; i += PANIC_TIMER_STEP) {
touch_softlockup_watchdog();
if (i >= i_next) {
_

Patches currently in -mm which might be from feng.tang@intel.com are

panic-add-options-to-print-system-info-when-panic-happens.patch
kernel-sysctl-add-panic_print-into-sysctl.patch
panic-avoid-the-extra-noise-dmesg.patch