On Mon, Dec 15, 2025 at 02:38:52PM +0100, Marco Elver wrote:
> Working on rebasing this to v6.19-rc1 and saw this new scoped seqlock
> abstraction. For that one I was able to make it work like I thought we
> could (below). Some awkwardness is required to make it work in
> for-loops, which only let you define variables with the same type.
>
> diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
> index b5563dc83aba..5162962b4b26 100644
> --- a/include/linux/seqlock.h
> +++ b/include/linux/seqlock.h
> @@ -1249,6 +1249,7 @@ struct ss_tmp {
> };
>
> static __always_inline void __scoped_seqlock_cleanup(struct ss_tmp *sst)
> + __no_context_analysis
> {
> if (sst->lock)
> spin_unlock(sst->lock);
> @@ -1278,6 +1279,7 @@ extern void __scoped_seqlock_bug(void);
>
> static __always_inline void
> __scoped_seqlock_next(struct ss_tmp *sst, seqlock_t *lock, enum ss_state
> target)
> + __no_context_analysis
> {
> switch (sst->state) {
> case ss_done:
> @@ -1320,9 +1322,18 @@ __scoped_seqlock_next(struct ss_tmp *sst, seqlock_t
> *lock, enum ss_state target)
> }
> }
>
> +/*
> + * Context analysis helper to release seqlock at the end of the for-scope;
> the
> + * alias analysis of the compiler will recognize that the pointer @s is is an
> + * alias to @_seqlock passed to read_seqbegin(_seqlock) below.
> + */
> +static __always_inline void __scoped_seqlock_cleanup_ctx(struct ss_tmp **s)
> + __releases_shared(*((seqlock_t **)s)) __no_context_analysis {}
> +
> #define __scoped_seqlock_read(_seqlock, _target, _s) \
> for (struct ss_tmp _s __cleanup(__scoped_seqlock_cleanup) = \
> - { .state = ss_lockless, .data = read_seqbegin(_seqlock) }; \
> + { .state = ss_lockless, .data = read_seqbegin(_seqlock) }, \
> + *__UNIQUE_ID(ctx) __cleanup(__scoped_seqlock_cleanup_ctx) =
> (struct ss_tmp *)_seqlock; \
> _s.state != ss_done; \
> __scoped_seqlock_next(&_s, _seqlock, _target))
>
I am ever so confused.. where is the __acquire_shared(), in read_seqbegin() ?
Also, why do we need this second variable with cleanup; can't the
existing __scoped_seqlock_cleanup() get the __releases_shared()
attribute?
