• Feng Tang's avatar
    panic: avoid the extra noise dmesg · c39ea0b9
    Feng Tang authored
    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 overridden 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.
    
    Adding a flag "suppress_printk" which gets set in panic() to avoid those
    noisy messages, without changing current kernel behavior that both panic
    blinking and sysrq magic key can work as is, suggested by Petr Mladek.
    
    To verify this, make sure kernel is not configured to reboot on panic and
    in console
     # echo c > /proc/sysrq-trigger
    to see if console only prints out the panic call stack.
    
    Link: http://lkml.kernel.org/r/1551430186-24169-1-git-send-email-feng.tang@intel.comSigned-off-by: default avatarFeng Tang <feng.tang@intel.com>
    Suggested-by: default avatarPetr Mladek <pmladek@suse.com>
    Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
    Acked-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
    Acked-by: default avatarSergey Senozhatsky <sergey.senozhatsky@gmail.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Kees Cook <keescook@chromium.org>
    Cc: Borislav Petkov <bp@suse.de>
    Cc: Andi Kleen <ak@linux.intel.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Jiri Slaby <jslaby@suse.com>
    Cc: Sasha Levin <sashal@kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    c39ea0b9
sysrq.c 26.3 KB