Re: linux-next: Tree for September 3

[Ingo Molnar]

* Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:

> On Thu, 4 Sep 2008, Andrew Morton wrote:
> > > 
> > > Cute, NULL pointer in the timer check code. Can you please addr2line
> > > the exact code line or upload the vmlinux somewhere ?
> > > 
> > 
> > erm, I might have lost that binary, and it only happened the once.  It
> > happened shortly after the machine had fully booted, during
> > establishment of the first sshd session.
> > 
> > It nuked the machine really well, too.  I had to pull the battery to
> > get it back.
> 
> Known problem on Sonys. :(
> 
> > fwiw:
> >
> > (gdb) l *0xc0126e7f
> > 0xc0126e7f is in get_next_timer_interrupt (kernel/timer.c:863).
> > warning: Source file is more recent than executable.
> > 858             for (array = 0; array < 4; array++) {
> > 859                     struct tvec *varp = varray[array];
> > 860     
> > 861                     index = slot = timer_jiffies & TVN_MASK;
> > 862                     do {
> > 863                             list_for_each_entry(nte, varp->vec + slot, entry) {
> > 864                                     found = 1;
> > 865                                     if (time_before(nte->expires, expires))
> > 866                                             expires = nte->expires;
> > 867                             }
> > 
> > which looks reasonable.
> 
> Yeah, as Linus decoded it's that loop. So we look at some corrupted
> entry here. 
> 
> CONFIG_DEBUG_OBJECTS (add debug_objects to the command line as well)
> should catch it when this is a timer being discarded, freed or
> reinitialized.
> 
> Otherwise, when it is just random corruption it wont help much.

i guess CONFIG_DEBUG_OBJECTS_TIMERS=y is practical, and 
CONFIG_DEBUG_LIST=y would be nice as well - it can catch memory 
corruptions rather early and is relatively light-weight.

[ and if there's any reproducability of the corruption and if it happens 
  at a stable kernel address then a small custom hack in ftrace can 
  catch it the moment it happens. ]

	Ingo
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