linux-kernel - Re: [PATCH 1/3] locking/ww_mutex: cleanup lock->ctx usage in amdgpu

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Date:   Tue, 20 Feb 2018 13:35:32 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christian König 
        <ckoenig.leichtzumerken@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] locking/ww_mutex: cleanup lock->ctx usage in amdgpu


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.