lkml.org 
[lkml]   [2011]   [Jun]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [debug patch] printk: Add a printk killswitch to robustify NMI watchdog messages

* 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


\
 
 \ /
  Last update: 2011-06-05 21:47    [W:0.206 / U:0.368 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site