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;
> >
