Messages in this thread Patch in this message | | | Date | Fri, 22 Feb 2019 14:09:59 +0800 | From | Feng Tang <> | Subject | Re: [PATCH v5] panic: Avoid the extra noise dmesg |
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One small cleanup of unneeded change in last post:
From 4ecbdfe1b398aa2285a696392eddeffb109d5463 Mon Sep 17 00:00:00 2001 From: Feng Tang <feng.tang@intel.com> Date: Thu, 21 Feb 2019 16:23:32 +0800 Subject: [PATCH v5] 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 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 panic_suppress_printk to avoid those noisy message, without changing the 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.
Suggested-by: Petr Mladek <pmladek@suse.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: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> Cc: Petr Mladek <pmladek@suse.com> Cc: Steven Rostedt <rostedt@goodmis.org> 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> --- Change log:
v5: - use a flag to notify printk not to print unimportant messages, while keep panic blinking and sysrq working, as suggested by Petr Mladek
v4: - make the local_irq_enable conditional and default off to cover possible use of interrupt/scheduling, as mentioned by Sergey and Petr
v3: - Make the change log clearer as suggested by Andrew Morton
v2: - Move the solution from hacking arch/scheduler code back to panic.c
drivers/tty/sysrq.c | 6 ++++++ include/linux/kernel.h | 1 + kernel/panic.c | 5 +++++ kernel/printk/printk.c | 4 ++++ 4 files changed, 16 insertions(+)
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index 1f03078..763e24c 100644 --- a/drivers/tty/sysrq.c +++ b/drivers/tty/sysrq.c @@ -527,8 +527,12 @@ void __handle_sysrq(int key, bool check_mask) { struct sysrq_key_op *op_p; int orig_log_level; + int orig_panic_suppress_printk; int i; + orig_panic_suppress_printk = panic_suppress_printk; + panic_suppress_printk = 0; + rcu_sysrq_start(); rcu_read_lock(); /* @@ -574,6 +578,8 @@ void __handle_sysrq(int key, bool check_mask) } rcu_read_unlock(); rcu_sysrq_end(); + + panic_suppress_printk = orig_panic_suppress_printk; } void handle_sysrq(int key) diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 8f0e68e..4120f3a 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -534,6 +534,7 @@ extern int panic_on_io_nmi; extern int panic_on_warn; extern int sysctl_panic_on_rcu_stall; extern int sysctl_panic_on_stackoverflow; +extern int panic_suppress_printk; extern bool crash_kexec_post_notifiers; diff --git a/kernel/panic.c b/kernel/panic.c index f121e6b..b9f004e 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -46,6 +46,8 @@ int panic_on_warn __read_mostly; int panic_timeout = CONFIG_PANIC_TIMEOUT; EXPORT_SYMBOL_GPL(panic_timeout); +int panic_suppress_printk; + #define PANIC_PRINT_TASK_INFO 0x00000001 #define PANIC_PRINT_MEM_INFO 0x00000002 #define PANIC_PRINT_TIMER_INFO 0x00000004 @@ -326,6 +328,9 @@ void panic(const char *fmt, ...) } #endif pr_emerg("---[ end Kernel panic - not syncing: %s ]---\n", buf); + + /* Do not scroll important messages printed above */ + panic_suppress_printk = 1; local_irq_enable(); for (i = 0; ; i += PANIC_TIMER_STEP) { touch_softlockup_watchdog(); diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index d3d1703..d460144 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1899,6 +1899,10 @@ asmlinkage int vprintk_emit(int facility, int level, unsigned long flags; u64 curr_log_seq; + /* Suppress unimportant messages after panic happens */ + if (unlikely(panic_suppress_printk)) + return 0; + if (level == LOGLEVEL_SCHED) { level = LOGLEVEL_DEFAULT; in_sched = true; -- 2.7.4
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