Re: [PATCH] drm/i915: Check the timeout passed to i915_wait_request

From: Daniel Vetter <daniel@ffwll.ch>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: intel-gfx@lists.freedesktop.org,
	Lionel Landwerlin <lionel.g.landwerlin@linux.intel.com>,
	Tvrtko Ursulin <tvrtko.ursulin@intel.com>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	stable@vger.kernel.org
Subject: Re: [PATCH] drm/i915: Check the timeout passed to i915_wait_request
Date: Thu, 26 Nov 2015 15:49:00 +0100	[thread overview]
Message-ID: <20151126144900.GT17050@phenom.ffwll.local> (raw)
In-Reply-To: <1448544702-5594-1-git-send-email-chris@chris-wilson.co.uk>

On Thu, Nov 26, 2015 at 01:31:42PM +0000, Chris Wilson wrote:
> We have relied upon the sole caller (wait_ioctl) validating the timeout
> argument. However, when waiting for multiple requests I forgot to ensure
> that the timeout was still positive on the later requests. This is more
> simply done inside __i915_wait_request.
> 
> Fixes regression introduced in
> commit b47161858ba13c9c7e03333132230d66e008dd55
> Author: Chris Wilson <chris@chris-wilson.co.uk>
> Date:   Mon Apr 27 13:41:17 2015 +0100
> 
>     drm/i915: Implement inter-engine read-read optimisations
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Lionel Landwerlin <lionel.g.landwerlin@linux.intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: stable@vger.kernel.org

Commit message should explain what the actual problem is - we add 1 jiffy
of delay for each wait_request, potentially waiting quite a bit longer
than what userspace asked for.

And not sure this really justifies for cc: stable, since all the wait
syscalls reserve the right to wait longer. Of course we should fix it,
just to keep validating this possible.

So with the commit message amended and cc: stable dropped this is
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  drivers/gpu/drm/i915/i915_gem.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 73c2c48729ec..8c19a980f5e6 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1210,8 +1210,16 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
>  	if (i915_gem_request_completed(req, true))
>  		return 0;
>  
> -	timeout_expire = timeout ?
> -		jiffies + nsecs_to_jiffies_timeout((u64)*timeout) : 0;
> +	timeout_expire = 0;
> +	if (timeout) {
> +		if (WARN_ON(*timeout < 0))
> +			return -EINVAL;
> +
> +		if (*timeout == 0)
> +			return -ETIME;
> +
> +		timeout_expire = jiffies + nsecs_to_jiffies_timeout(*timeout);
> +	}
>  
>  	if (INTEL_INFO(dev_priv)->gen >= 6)
>  		gen6_rps_boost(dev_priv, rps, req->emitted_jiffies);
> -- 
> 2.6.2
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch