Re: [RFC][PATCH] kprobes: Add separate preempt_disabling forkprobes

[Steven Rostedt]

On Fri, 2011-07-01 at 14:09 +0900, Masami Hiramatsu wrote:

> BTW, on my tip tree, add_preempt_count (a.k.a. inc_preempt_count())
> is marked as __kprobes, so it can not be probed. Is there any change?
> 

That is when debug or preempt tracer is enabled. Otherwise it's
hardcoded into whatever calls it:

#if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER)
  extern void add_preempt_count(int val);
  extern void sub_preempt_count(int val);
#else
# define add_preempt_count(val)	do { preempt_count() += (val); } while (0)
# define sub_preempt_count(val)	do { preempt_count() -= (val); } while (0)
#endif


Anyway, it still doesn't help the place that reads preempt_count() and
then later uses the result. I hit the crash in schedule_bug() where it
increments preempt count, then reads it to see if it is only 1.

-- Steve


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