[PATCH 1/4] drm/msm: Fix improper uses of smp_mb__{before,after}_atomic()

[Jordan Crouse]

On Mon, May 20, 2019 at 07:23:55PM +0200, Andrea Parri wrote:
> These barriers only apply to the read-modify-write operations; in
> particular, they do not apply to the atomic_set() primitive.
> 
> Replace the barriers with smp_mb()s.
> 
> Fixes: b1fc2839d2f92 ("drm/msm: Implement preemption for A5XX targets")
> Cc: stable at vger.kernel.org
> Reported-by: "Paul E. McKenney" <paulmck at linux.ibm.com>
> Reported-by: Peter Zijlstra <peterz at infradead.org>
> Signed-off-by: Andrea Parri <andrea.parri at amarulasolutions.com>
> Cc: Rob Clark <robdclark at gmail.com>
> Cc: Sean Paul <sean at poorly.run>
> Cc: David Airlie <airlied at linux.ie>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Cc: Jordan Crouse <jcrouse at codeaurora.org>
> Cc: linux-arm-msm at vger.kernel.org
> Cc: dri-devel at lists.freedesktop.org
> Cc: freedreno at lists.freedesktop.org
> Cc: "Paul E. McKenney" <paulmck at linux.ibm.com>
> Cc: Peter Zijlstra <peterz at infradead.org>

I'll go ahead and ack this - I'm not super clued in on atomic barriers, but this
seems to be in the spirit of what we are trying to do to protect the atomic
value. Rob can disagree, of course.

Acked-by: Jordan Crouse <jcrouse at codeaurora.org>

> ---
>  drivers/gpu/drm/msm/adreno/a5xx_preempt.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/a5xx_preempt.c b/drivers/gpu/drm/msm/adreno/a5xx_preempt.c
> index 3d62310a535fb..ee0820ee0c664 100644
> --- a/drivers/gpu/drm/msm/adreno/a5xx_preempt.c
> +++ b/drivers/gpu/drm/msm/adreno/a5xx_preempt.c
> @@ -39,10 +39,10 @@ static inline void set_preempt_state(struct a5xx_gpu *gpu,
>  	 * preemption or in the interrupt handler so barriers are needed
>  	 * before...
>  	 */
> -	smp_mb__before_atomic();
> +	smp_mb();
>  	atomic_set(&gpu->preempt_state, new);
>  	/* ... and after*/
> -	smp_mb__after_atomic();
> +	smp_mb();
>  }
>  
>  /* Write the most recent wptr for the given ring into the hardware */
> -- 
> 2.7.4
> 

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