On Fri 2019-03-01 12:11:31, Feng Tang wrote: > Hi Andrew, > > Thanks for the review! > > On Thu, Feb 28, 2019 at 12:00:14PM -0800, Andrew Morton wrote: > > On Fri, 22 Feb 2019 14:09:59 +0800 Feng Tang <[email protected]> wrote: > > > > > 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 > > > > It's a fairly ugly-looking patch but I am inclined to agree. > > Yes, it's ugly :) we've changed 3 methods to tackle this. > > > The panicing CPU is spinning and blinking a LED and all CPUs have > > interrupts enabled and the system is known to be in a messed up state. > > All sorts of kernel code could emit all sorts of output in such > > circumstances. So a global printk-killing knob seems appropriate. > > > > Thoughts: > > > > - why do the suppression in vprintk_emit()? Doing it right at entry > > to printk() seems cleaner, more explicit? > > Yes, I put it in printk() in one earlier post, and Petr suggested to > put it into vprintk_emit so that it works for all printk() interfaces, > like the devkmsg_write -> printk_emit -> vprintk_emit path.
Yes, there are more printk interfaces. The check in vprintk_emit() allows to calm down also prink_deferred() and dev_printk(). > > - Other code sites may wish to suppress all printks. Perhaps > > `panic_suppress_printk' should just be called `suppress_printk'? > Ok, then I'll move the definition from panic.c to printk code. This change looks fine to me. Best Regards, Petr PS: I am sorry for the late review. I have spent many days with reviewing a proposal of rewrite of printk() internals.
