* seqlock:do_raw_write_seqcount_end smp_wmb
@ 2023-08-24 1:07 Kassey Li
2023-08-24 6:13 ` Pavan Kondeti
0 siblings, 1 reply; 2+ messages in thread
From: Kassey Li @ 2023-08-24 1:07 UTC (permalink / raw)
To: Peter Zijlstra, mingo, will, boqun.feng, LKML
hi, Peter:
I not quit sure on this, but is that a type error in
do_raw_write_seqcount_end here ?
is this change necessary to match with do_raw_write_seqcount_begin ?
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 987a59d977c5..eb8807ed3a00 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -486,8 +486,8 @@ do {
\
static inline void do_raw_write_seqcount_end(seqcount_t *s)
{
- smp_wmb();
s->sequence++;
+ smp_wmb();
kcsan_nestable_atomic_end();
}
to match with
static inline void do_raw_write_seqcount_begin(seqcount_t *s)
{
kcsan_nestable_atomic_begin();
s->sequence++;
smp_wmb();
}
BR
TNT
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: seqlock:do_raw_write_seqcount_end smp_wmb
2023-08-24 1:07 seqlock:do_raw_write_seqcount_end smp_wmb Kassey Li
@ 2023-08-24 6:13 ` Pavan Kondeti
0 siblings, 0 replies; 2+ messages in thread
From: Pavan Kondeti @ 2023-08-24 6:13 UTC (permalink / raw)
To: Kassey Li; +Cc: Peter Zijlstra, mingo, will, boqun.feng, LKML
On Thu, Aug 24, 2023 at 09:07:57AM +0800, Kassey Li wrote:
> hi, Peter:
> I not quit sure on this, but is that a type error in
> do_raw_write_seqcount_end here ?
> is this change necessary to match with do_raw_write_seqcount_begin ?
>
>
> diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
> index 987a59d977c5..eb8807ed3a00 100644
> --- a/include/linux/seqlock.h
> +++ b/include/linux/seqlock.h
> @@ -486,8 +486,8 @@ do { \
>
> static inline void do_raw_write_seqcount_end(seqcount_t *s)
> {
> - smp_wmb();
> s->sequence++;
> + smp_wmb();
> kcsan_nestable_atomic_end();
> }
>
>
> to match with
>
> static inline void do_raw_write_seqcount_begin(seqcount_t *s)
> {
> kcsan_nestable_atomic_begin();
> s->sequence++;
> smp_wmb();
> }
>
>
>
I don't see anything wrong here. As per my understanding,
do_raw_write_seqcount_end() marks the end of the writer side critical
section. The data modified in the critical section should be visisble to
the *reader* before seqcount::sequence increment is visible. The
smp_wmb() here pairs with the smp_rmb() in the read_seqcount_begin().
Pls see kernel/sched/cputime.c for an example.
Thanks,
Pavan
^ permalink raw reply [flat|nested] 2+ messages in thread
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