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")
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;
>
