Re: [tip: locking/core] locking/qspinlock: Fix 'wait_early' set but not used warning

[Waiman Long]

On 3/11/24 06:57, Ingo Molnar wrote:
> * tip-bot2 for Waiman Long <tip-bot2@xxxxxxxxxxxxx> wrote:
>
> > The following commit has been merged into the locking/core branch of tip:
> >
> > Commit-ID:     ca4bc2e07b716509fd279d2b449bb42f4263a9c8
> > Gitweb:        https://git.kernel.org/tip/ca4bc2e07b716509fd279d2b449bb42f4263a9c8
> > Author:        Waiman Long <longman@xxxxxxxxxx>
> > AuthorDate:    Thu, 22 Feb 2024 10:05:37 -05:00
> > Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
> > CommitterDate: Wed, 28 Feb 2024 13:08:37 +01:00
> >
> > locking/qspinlock: Fix 'wait_early' set but not used warning
> >
> > When CONFIG_LOCK_EVENT_COUNTS is off, the wait_early variable will be
> > set but not used. This is expected. Recent compilers will not generate
> > wait_early code in this case.
> >
> > Add the __maybe_unused attribute to wait_early for suppressing this
> > W=1 warning.
> >
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
> > Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
> > Reviewed-by: Boqun Feng <boqun.feng@xxxxxxxxx>
> > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Link: https://lore.kernel.org/r/20240222150540.79981-2-longman@xxxxxxxxxx
> >
> > Closes: https://lore.kernel.org/oe-kbuild-all/202312260422.f4pK3f9m-lkp@xxxxxxxxx/
> > ---
> >   kernel/locking/qspinlock_paravirt.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
> > index 6a0184e..ae2b12f 100644
> > --- a/kernel/locking/qspinlock_paravirt.h
> > +++ b/kernel/locking/qspinlock_paravirt.h
> > @@ -294,8 +294,8 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
> >   {
> >   	struct pv_node *pn = (struct pv_node *)node;
> >   	struct pv_node *pp = (struct pv_node *)prev;
> > +	bool __maybe_unused wait_early;
> >   	int loop;
> > -	bool wait_early;
> On a second thought, shouldn't this be solved via lockevent_cond_inc()'s
> !CONFIG_LOCK_EVENT_COUNTS stub explicitly marking the variable as used, via
> !something like:
>
>     #define lockevent_cond_inc(ev, c)		do { (void)(c); } while (0)
>
> or so, instead of uglifying the usage site?

Right, that should work too. Thanks for the suggestion. I will post 
another to do that.

Cheers,
Longman