From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Vetter Subject: Re: [PATCH v3] drm/i915: Gracefully handle obj not bound to GGTT in is_pin_display Date: Fri, 16 May 2014 16:25:30 +0200 Message-ID: <20140516142530.GJ8790@phenom.ffwll.local> References: <1400238502-10299-1-git-send-email-oscar.mateo@intel.com> <1400246443-13320-1-git-send-email-oscar.mateo@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-ee0-f52.google.com (mail-ee0-f52.google.com [74.125.83.52]) by gabe.freedesktop.org (Postfix) with ESMTP id 3411E6EFC9 for ; Fri, 16 May 2014 07:25:35 -0700 (PDT) Received: by mail-ee0-f52.google.com with SMTP id e53so1591275eek.25 for ; Fri, 16 May 2014 07:25:34 -0700 (PDT) Content-Disposition: inline In-Reply-To: <1400246443-13320-1-git-send-email-oscar.mateo@intel.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" To: oscar.mateo@intel.com Cc: intel-gfx@lists.freedesktop.org List-Id: intel-gfx@lists.freedesktop.org On Fri, May 16, 2014 at 02:20:43PM +0100, oscar.mateo@intel.com wrote: > From: Oscar Mateo > > Otherwise, we do a NULL pointer dereference. > > I've seen this happen while handling an error in > i915_gem_object_pin_to_display_plane(): > > If i915_gem_object_set_cache_level() fails, we call is_pin_display() > to handle the error. At this point, the object is still not pinned > to GGTT and maybe not even bound, so we have to check before we > dereference its GGTT vma. > > The IGT kms_flip/bo-too-big tests for this bug. > > v2: Chris Wilson says restoring the old value is easier, but that > is_pin_display is useful as a theory of operation. Take the solomonic > decision: at least this way is_pin_display is a little more robust > (until Chris can kill it off). > > v3: Chris suggests the WARN in i915_gem_obj_to_ggtt has outlived its > usefulness: add a reminder to remove it. > > Issue: VIZ-3772 > Signed-off-by: Oscar Mateo Queued for -next, thanks for the patch. -Daniel > --- > drivers/gpu/drm/i915/i915_gem.c | 19 +++++++++++++++++-- > 1 file changed, 17 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c > index 034ba2c..f6c0351 100644 > --- a/drivers/gpu/drm/i915/i915_gem.c > +++ b/drivers/gpu/drm/i915/i915_gem.c > @@ -3641,6 +3641,15 @@ unlock: > > static bool is_pin_display(struct drm_i915_gem_object *obj) > { > + struct i915_vma *vma; > + > + if (list_empty(&obj->vma_list)) > + return false; > + > + vma = i915_gem_obj_to_ggtt(obj); > + if (!vma) > + return false; > + > /* There are 3 sources that pin objects: > * 1. The display engine (scanouts, sprites, cursors); > * 2. Reservations for execbuffer; > @@ -3652,7 +3661,7 @@ static bool is_pin_display(struct drm_i915_gem_object *obj) > * subtracting the potential reference by the user, any pin_count > * remains, it must be due to another use by the display engine. > */ > - return i915_gem_obj_to_ggtt(obj)->pin_count - !!obj->user_pin_count; > + return vma->pin_count - !!obj->user_pin_count; > } > > /* > @@ -3666,6 +3675,7 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj, > struct intel_ring_buffer *pipelined) > { > u32 old_read_domains, old_write_domain; > + bool was_pin_display; > int ret; > > if (pipelined != obj->ring) { > @@ -3677,6 +3687,7 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj, > /* Mark the pin_display early so that we account for the > * display coherency whilst setting up the cache domains. > */ > + was_pin_display = obj->pin_display; > obj->pin_display = true; > > /* The display engine is not coherent with the LLC cache on gen6. As > @@ -3719,7 +3730,8 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj, > return 0; > > err_unpin_display: > - obj->pin_display = is_pin_display(obj); > + WARN_ON(was_pin_display != is_pin_display(obj)); > + obj->pin_display = was_pin_display; > return ret; > } > > @@ -5115,6 +5127,9 @@ struct i915_vma *i915_gem_obj_to_ggtt(struct drm_i915_gem_object *obj) > { > struct i915_vma *vma; > > + /* This WARN has probably outlived its usefulness (callers already > + * WARN if they don't find the GGTT vma they expect). When removing, > + * remember to remove the pre-check in is_pin_display() as well */ > if (WARN_ON(list_empty(&obj->vma_list))) > return NULL; > > -- > 1.9.0 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch