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Subject: Re: [PATCH 1/3] locking/ww_mutex: cleanup lock->ctx usage in amdgpu
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
References: <20180215141944.4332-1-christian.koenig@amd.com>
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From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
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Date:   Tue, 20 Feb 2018 14:08:26 +0100
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Am 20.02.2018 um 13:35 schrieb Peter Zijlstra:
> This really should've been Cc'ed to me.
>
> On Thu, Feb 15, 2018 at 03:19:42PM +0100, Christian König wrote:
>> diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h
>> index 39fda195bf78..dd580db289e8 100644
>> --- a/include/linux/ww_mutex.h
>> +++ b/include/linux/ww_mutex.h
>> @@ -358,4 +358,21 @@ static inline bool ww_mutex_is_locked(struct ww_mutex *lock)
>>   	return mutex_is_locked(&lock->base);
>>   }
>>   
>> +/**
>> + * ww_mutex_is_owned_by - is the w/w mutex locked by this task in that context
>> + * @lock: the mutex to be queried
>> + * @task: the task structure to check
>> + * @ctx: the w/w acquire context to test
>> + *
>> + * Returns true if the mutex is locked in the context by the given task, false
>> + * otherwise.
>> + */
>> +static inline bool ww_mutex_is_owned_by(struct ww_mutex *lock,
>> +					struct task_struct *task,
>> +					struct ww_acquire_ctx *ctx)
>> +{
>> +	return likely(__mutex_owner(&lock->base) == task) &&
>> +		READ_ONCE(lock->ctx) == ctx;
>> +}
> Nak on that interface, that's racy and broken by design.

Why?

Regards,
Christian.