Re: [PATCH v2] CodeSamples/defer: Fix hazard torture

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On Sat, Apr 22, 2023 at 08:56:17PM +0900, Akira Yokosawa wrote:
> On Sat, 22 Apr 2023 10:34:21 +0000, Alan Huang wrote:
> > Because hp_try_record() must check for concurrent modifications,
> > we should not dereference the pointer. The arg of hazptr_read_stress_test
> > is always NULL, which is designated at time when create the thread,
> > therefore, all threads will store their hazard pointer in the same slot.
> > Also, hazptr_thread_exit will clear their own hazard pointer from
> > smp_thread_id() * K.
> > 
> > Signed-off-by: Alan Huang <mmpgouride@xxxxxxxxx>
> 
> Now I see all your points.  Thank you for your thorough review
> of the code!
> 
> As I mentioned earlier, the deref of p was introduced by commit
> a082aba85ce0 ("defer/hazptr: Checkpoint for text/code update"),
> while the uses of arg in hazptr_read_stress_test() and
> hazptr_read_perf_test() were there since the addition of this code
> by commit c672535d475a ("Convert Tom Hart's hazard-pointer
> implementation to perfbook"), that is, if I'm reading the code
> correctly.
> 
> So,
> 
> Reviewed-by: Akira Yokosawa <akiyks@xxxxxxxxx>
> Fixes: c672535d475a ("Convert Tom Hart's hazard-pointer implementation to perfbook")
> Fixes: a082aba85ce0 ("defer/hazptr: Checkpoint for text/code update")

Now -that- is what I call an embarrassing bug!

Thank you both for tracking it down and for the fix!!!

Queued and pushed.

							Thanx, Paul

>         Thanks, Akira
> 
> > ---
> >  CodeSamples/defer/hazptr.h        | 2 +-
> >  CodeSamples/defer/hazptrtorture.h | 5 ++---
> >  2 files changed, 3 insertions(+), 4 deletions(-)
> > 
> > diff --git a/CodeSamples/defer/hazptr.h b/CodeSamples/defer/hazptr.h
> > index 759ab53d..e061303d 100644
> > --- a/CodeSamples/defer/hazptr.h
> > +++ b/CodeSamples/defer/hazptr.h
> > @@ -87,7 +87,7 @@ static inline void *hp_record(void **p,			//\lnlbl{hr:b}
> >  	void *tmp;
> >  
> >  	do {
> > -		tmp = hp_try_record(*p, hp);
> > +		tmp = hp_try_record(p, hp);
> >  	} while (tmp == (void *)HAZPTR_POISON);
> >  	return tmp;
> >  }							//\lnlbl{hr:e}
> > diff --git a/CodeSamples/defer/hazptrtorture.h b/CodeSamples/defer/hazptrtorture.h
> > index 53efa259..acdd532b 100644
> > --- a/CodeSamples/defer/hazptrtorture.h
> > +++ b/CodeSamples/defer/hazptrtorture.h
> > @@ -99,7 +99,7 @@ void *hazptr_read_perf_test(void *arg)
> >  {
> >  	int i;
> >  	int me = (long)arg;
> > -	int base = me * K;
> > +	int base = smp_thread_id() * K;
> >  	long long n_reads_local = 0;
> >  	hazptr_head_t hh;
> >  	hazptr_head_t *hhp = &hh;
> > @@ -241,8 +241,7 @@ DEFINE_PER_THREAD(long long [HAZPTR_STRESS_PIPE_LEN + 1], hazptr_stress_count);
> >  
> >  void *hazptr_read_stress_test(void *arg)
> >  {
> > -	int me = (int)(long)arg;
> > -	int base = me * K;
> > +	int base = smp_thread_id() * K;
> >  	struct hazptr_stress *p;
> >  	int pc;
> >  



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