Re: [RFC][PATCH 1/9] seqlock/latch: Provide raw_read_seqcount_latch_retry()

Thomas Gleixner
2023-05-09T08:13:29Z

On Mon, May 08 2023 at 23:19, Peter Zijlstra wrote:
> The read side of seqcount_latch consists of:
>
> do {
> seq = raw_read_seqcount_latch(&latch->seq);
> ...
> } while (read_seqcount_latch_retry(&latch->seq, seq));
>
> which is asymmetric in the raw_ department, and sure enough,
> read_seqcount_latch_retry() includes (explicit) instrumentation where
> raw_read_seqcount_latch() does not.
>
> This inconsistency becomes a problem when trying to use it from
> noinstr code. As such, fix it by renaming and re-implementing
> raw_read_seqcount_latch_retry() without the instrumentation.
>
> Specifically the instrumentation in question is kcsan_atomic_next(0)
> in do___read_seqcount_retry(). Loosing this annotation is not a
> problem because raw_read_seqcount_latch() does not pass through
> kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX).
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>