linux-kernel - Re: [tip: locking/core] locking/qspinlock: Fix 'wait

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Date: Mon, 11 Mar 2024 09:45:55 -0400
From: Waiman Long <longman@...hat.com>
To: Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Cc: linux-tip-commits@...r.kernel.org, kernel test robot <lkp@...el.com>,
 Boqun Feng <boqun.feng@...il.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org
Subject: Re: [tip: locking/core] locking/qspinlock: Fix 'wait_early' set but
 not used warning

On 3/11/24 06:57, Ingo Molnar wrote:
> * tip-bot2 for Waiman Long <tip-bot2@...utronix.de> 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@...hat.com>
>> AuthorDate:    Thu, 22 Feb 2024 10:05:37 -05:00
>> Committer:     Ingo Molnar <mingo@...nel.org>
>> 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@...el.com>
>> Signed-off-by: Waiman Long <longman@...hat.com>
>> Signed-off-by: Ingo Molnar <mingo@...nel.org>
>> Reviewed-by: Boqun Feng <boqun.feng@...il.com>
>> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>> Link: https://lore.kernel.org/r/20240222150540.79981-2-longman@redhat.com
>>
>> Closes: https://lore.kernel.org/oe-kbuild-all/202312260422.f4pK3f9m-lkp@intel.com/
>> ---
>>   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