On Mon, Mar 25, 2024 at 11:16:27AM +0100, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@xxxxxxxxx>
>
> When using "guard(rcu)();" sparse will complain, because even
> though it now understands the cleanup attribute, it doesn't
> evaluate the calls from it at function exit, and thus doesn't
> count the context correctly.
>
> Given that there's a conditional in the resulting code:
>
> static inline void class_rcu_destructor(class_rcu_t *_T)
> {
> if (_T->lock) {
> rcu_read_unlock();
> }
> }
>
> it seems that even trying to teach sparse to evalulate the
> cleanup attribute function it'd still be difficult to really
> make it understand the full context here.
>
> Suppress the sparse warning by just releasing the context in
> the acquisition part of the function, after all we know it's
> safe with the guard, that's the whole point of it.
>
> Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
> ---
> include/linux/rcupdate.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 17d7ed5f3ae6..41081ee9c9a7 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -1090,6 +1090,6 @@ rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
> extern int rcu_expedited;
> extern int rcu_normal;
>
> -DEFINE_LOCK_GUARD_0(rcu, rcu_read_lock(), rcu_read_unlock())
> +DEFINE_LOCK_GUARD_0(rcu, do { rcu_read_lock(); __release(RCU); } while(0), rcu_read_unlock())
>
Hmm.. not a big fan of this. __release(RCU) following a rcu_read_lock()
is really confusing. Maybe we can introduce a _rcu_read_lock():
void _rcu_read_lock(bool guard) {
__rcu_read_lock();
// Skip sparse annotation in "guard(rcu)()" to work
// around sparse's lack of support of cleanup.
if (!guard)
__acquire(RCU);
rcu_lock_acquire(...);
...
}
and normal rcu_read_lock() is just a _rcu_read_lock(false), RCU guard is
a _rcu_read_lock(true)?
But before that how does it looks if we don't fix this entirely? ;-)
Regards,
Boqun
> #endif /* __LINUX_RCUPDATE_H */
> --
> 2.44.0
>
