On Mon, Mar 25, 2024 at 10:41:36AM -0700, Boqun Feng wrote:
> On Mon, Mar 25, 2024 at 06:39:08PM +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>
>
> Reviewed-by: Boqun Feng <boqun.feng@xxxxxxxxx>
Queued, thank you both!
Thanx, Paul
> Regards,
> Boqun
>
> > ---
> > v2: add a comment after discussion with Boqun
> >
> > ---
> > include/linux/rcupdate.h | 14 +++++++++++++-
> > 1 file changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > index 0746b1b0b663..6a3c52b3c180 100644
> > --- a/include/linux/rcupdate.h
> > +++ b/include/linux/rcupdate.h
> > @@ -1059,6 +1059,18 @@ 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();
> > + /*
> > + * sparse doesn't call the cleanup function,
> > + * so just release immediately and don't track
> > + * the context. We don't need to anyway, since
> > + * the whole point of the guard is to not need
> > + * the explicit unlock.
> > + */
> > + __release(RCU);
> > + } while(0),
> > + rcu_read_unlock())
> >
> > #endif /* __LINUX_RCUPDATE_H */
> > --
> > 2.44.0
> >
