On Fri, Oct 04, 2019 at 10:29:17AM +0100, Russell King - ARM Linux admin wrote:
On Fri, Oct 04, 2019 at 11:11:42AM +0200, Petr Mladek wrote:
On Thu 2019-10-03 21:56:34, Will Deacon wrote:
I've deliberately left the irq part alone, since I think having magic sysrq work via the keyboard interrupt is desirable from the panic loop.
I agree that we should keep sysrq working.
One pity thing is that led_panic_blink() in leds/drivers/trigger/ledtrig-panic.c uses workqueues:
- led_panic_blink()
- led_trigger_event()
- led_set_brightness()
- schedule_work()
It means that it depends on the scheduler. I guess that it does not work in many panic situations. But this patch will always block it.
I agree that it is strange that userspace still works at this stage. But does it cause any real problems?
Yes, there are watchdog drivers that continue to pat their watchdog after the kernel has panic'd. It makes watchdogs useless (which is exactly how this problem was discovered.)
Indeed, and I think the LED blinking is already unreliable if the brightness operation needs to sleep. For example, if the kernel isn't preemptible or the work gets queued up on a different CPU which is sitting in panic_smp_self_stop().
Will