linux-kernel - Re: [PATCH v3 05/12] locking/ww_mutex: Remove the __ww_mutex

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Date:   Fri, 23 Dec 2016 12:16:03 +0100
From:   Nicolai Hähnle <nhaehnle@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        Nicolai Hähnle <Nicolai.Haehnle@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Maarten Lankhorst <dev@...ankhorst.nl>,
        Daniel Vetter <daniel@...ll.ch>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v3 05/12] locking/ww_mutex: Remove the __ww_mutex_lock
 inline wrappers

On 23.12.2016 11:48, Peter Zijlstra wrote:
> On Wed, Dec 21, 2016 at 07:46:33PM +0100, Nicolai Hähnle wrote:
>> diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h
>> index a5960e5..b2eaaab 100644
>> --- a/include/linux/ww_mutex.h
>> +++ b/include/linux/ww_mutex.h
>> @@ -186,11 +186,6 @@ static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
>>  #endif
>>  }
>>
>> -extern int __must_check __ww_mutex_lock(struct ww_mutex *lock,
>> -					struct ww_acquire_ctx *ctx);
>> -extern int __must_check __ww_mutex_lock_interruptible(struct ww_mutex *lock,
>> -						      struct ww_acquire_ctx *ctx);
>> -
>>  /**
>>   * ww_mutex_lock - acquire the w/w mutex
>>   * @lock: the mutex to be acquired
>> @@ -220,10 +215,8 @@ extern int __must_check __ww_mutex_lock_interruptible(struct ww_mutex *lock,
>>   *
>>   * A mutex acquired with this function must be released with ww_mutex_unlock.
>>   */
>> -static inline int ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
>> -{
>> -	return __ww_mutex_lock(lock, ctx);
>> -}
>> +extern int __must_check ww_mutex_lock(struct ww_mutex *lock,
>> +				      struct ww_acquire_ctx *ctx);
>>
>>  /**
>>   * ww_mutex_lock_interruptible - acquire the w/w mutex, interruptible
>> @@ -255,11 +248,8 @@ static inline int ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ct
>>   *
>>   * A mutex acquired with this function must be released with ww_mutex_unlock.
>>   */
>> -static inline int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
>> -							   struct ww_acquire_ctx *ctx)
>> -{
>> -	return __ww_mutex_lock_interruptible(lock, ctx);
>> -}
>> +extern int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
>> +						    struct ww_acquire_ctx *ctx);
>>
>>  /**
>>   * ww_mutex_lock_slow - slowpath acquiring of the w/w mutex
>> diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
>> index a41bec2..282c6de 100644
>
> For some reason this patch appears to make lib/locking-selftest.c really
> unhappy.
>
> I get endless streams of:
>
> ../lib/locking-selftest.c: In function ‘ww_test_fail_acquire’:
> ../lib/locking-selftest.c:1141:6: error: void value not ignored as it ought to be
>   ret = WWL(&o, &t);
>       ^
>
> Apparently GCC gets confused about __much_check on inline functions or
> something, or I got the patch wrong.

Weird, I'm not getting that, and it makes no sense either from a quick 
glimpse of the code. Is there anything beside 
CONFIG_DEBUG_LOCKING_API_SELFTESTS I would have to enable to trigger 
this? FWIW:

$ gcc --version
gcc (Ubuntu 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609

>
>