Messages in this thread | | | Date | Sun, 5 Jun 2011 21:44:19 +0200 | From | Ingo Molnar <> | Subject | Re: [debug patch] printk: Add a printk killswitch to robustify NMI watchdog messages |
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* Arne Jansen <lists@die-jansens.de> wrote:
> From the timing I see I'd guess it has something to do with the > scheduler kicking in during printk. I'm neither familiar with the > printk code nor with the scheduler.
Yeah, that's the well-known wake-up of klogd:
void console_unlock(void) { ... up(&console_sem);
actually ... that's not the klogd wake-up at all (!). I so suck today at bug analysis :-)
It's the console lock()/unlock() sequence, and guess what does it:
drivers/tty/tty_io.c: console_lock(); drivers/tty/vt/selection.c: console_lock();
and the vt.c code in a dozen places.
So maybe it's some sort of tty related memory corruption that was made *visible* via the extra assert that the scheduler is doing? The pi_list is embedded in task struct.
This would explain why only printk() triggers it and other wakeup patterns not.
Now, i don't really like this theory either. Why is there no other type of corruption? And exactly why did only the task_struct::pi_lock field get corrupted while nearby fields not? Also, none of the fields near pi_lock are even remotely tty related.
Thanks,
Ingo
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