Re: [PATCH 1/2] drm/i915/psr: Fix race in intel_psr_work()

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Sun, Jun 24, 2018 at 10:47:40PM -0700, Dhinakaran Pandiyan wrote:
> Commit 5422b37c907e ("drm/i915/psr: Kill delays when activating psr
> back.") switched from delayed work to the plain variant and while doing so
> removed the check for work_busy() before scheduling a PSR activation.
> This appears to cause consecutive executions of psr_activate() in this
> scenario - after a worker picks up the PSR work item for execution and
> before the work function can acquire the PSR mutex, a psr_flush() can
> get hold of the mutex and schedule another PSR work. Without a psr_exit()
> between the two psr_activate() calls, warning messages get printed.
> Further, since we drop the mutex in the midst of psr_work() to wait for
> PSR to idle, another work item can also get scheduled. Fix this by
> returning if PSR was already active.

:( my bad again, sorry...

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

> 
> Fixes: 5422b37c907e ("drm/i915/psr: Kill delays when activating psr back.")
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106948
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: José Roberto de Souza <jose.souza@intel.com>
> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/intel_psr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_psr.c b/drivers/gpu/drm/i915/intel_psr.c
> index aea81ace854b..7aa324f0d1f7 100644
> --- a/drivers/gpu/drm/i915/intel_psr.c
> +++ b/drivers/gpu/drm/i915/intel_psr.c
> @@ -811,7 +811,7 @@ static void intel_psr_work(struct work_struct *work)
>  	 * recheck. Since psr_flush first clears this and then reschedules we
>  	 * won't ever miss a flush when bailing out here.
>  	 */
> -	if (dev_priv->psr.busy_frontbuffer_bits)
> +	if (dev_priv->psr.busy_frontbuffer_bits || dev_priv->psr.active)
>  		goto unlock;
>  
>  	intel_psr_activate(dev_priv->psr.enabled);
> -- 
> 2.14.1
> 
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