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SubjectRe: [GIT PULL] updates for oprofile
Ingo, et al., 

Regarding today's pulled request, containing:

commit bc078e4eab65f11bbaeed380593ab8151b30d703
Author: Martin Schwidefsky <>
Date: Tue Mar 2 16:01:10 2010 +0100

oprofile: convert oprofile from timer_hook to hrtimer

Information is a touch scant, as I'm doing the investigation as I
write, but I believe that that patch can cause ooops regressions
via a null-pointer dereference in oprofile_add_sample().

That function declares:
* Add a sample. This may be called from any context.
void oprofile_add_sample(struct pt_regs * const regs, unsigned long event);

And begins:
void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
int is_kernel = !user_mode(regs);

Where on at least two major architectures (Arm, x86), user_mode()
unconditionally dereferences its parameter.

Now oprofile_add_sample() is called from this context:
static enum hrtimer_restart oprofile_hrtimer_notify(struct hrtimer *hrtimer)
oprofile_add_sample(get_irq_regs(), 0);

And get_irq_regs() is NULL when not in an IRQ context.


An example of this kind of thing kicking in has already been encountered
last year:
(That thread got a little side-tracked onto OMAP specifics, but the
original report is topical.)

Now would be a very good time for the "many eyes" principle to kick in.

I'm now looking into workarounds, but nothing that I'd necessarily
want to submit as a real fix.

cc:'d replies appreciated

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