From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Vetter Subject: Re: [PATCH] drm/i915: Fix write-read race with multiple rings Date: Wed, 10 Jul 2013 10:41:47 +0200 Message-ID: <20130710084147.GJ18285@phenom.ffwll.local> References: <1373358159-11045-1-git-send-email-chris@chris-wilson.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-ea0-f170.google.com (mail-ea0-f170.google.com [209.85.215.170]) by gabe.freedesktop.org (Postfix) with ESMTP id 41735E5CF6 for ; Wed, 10 Jul 2013 01:41:46 -0700 (PDT) Received: by mail-ea0-f170.google.com with SMTP id h10so4885968eaj.1 for ; Wed, 10 Jul 2013 01:41:45 -0700 (PDT) Content-Disposition: inline In-Reply-To: <1373358159-11045-1-git-send-email-chris@chris-wilson.co.uk> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org Errors-To: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org To: Chris Wilson Cc: Daniel Vetter , intel-gfx@lists.freedesktop.org, stable@vger.kernel.org List-Id: intel-gfx@lists.freedesktop.org On Tue, Jul 09, 2013 at 09:22:39AM +0100, Chris Wilson wrote: > Daniel noticed a problem where is we wrote to an object with ring A in > the middle of a very long running batch, then executed a quick batch on > ring B before a batch that reads from the same object, its obj->ring would > now point to ring B, but its last_write_seqno would be still relative to > ring A. This would allow for the user to read from the object before the > GPU had completed the write, as set_domain would only check that ring B > had passed the last_write_seqno. > > To fix this simply (and inelegantly), we bump the last_write_seqno when > switching rings so that the last_write_seqno is always relative to the > current obj->ring. > > Signed-off-by: Chris Wilson > Cc: Daniel Vetter > Cc: stable@vger.kernel.org It was a bit trick, but I've stitched together an igt to exercise this bug. Picked up for -fixes, thanks for the patch. -Daniel > --- > drivers/gpu/drm/i915/i915_gem.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c > index 774620d..7c59cb1 100644 > --- a/drivers/gpu/drm/i915/i915_gem.c > +++ b/drivers/gpu/drm/i915/i915_gem.c > @@ -1954,6 +1954,10 @@ i915_gem_object_move_to_active(struct drm_i915_gem_object *obj, > u32 seqno = intel_ring_get_seqno(ring); > > BUG_ON(ring == NULL); > + if (obj->ring != ring && obj->last_write_seqno) { > + /* Keep the seqno relative to the current ring */ > + obj->last_write_seqno = seqno; > + } > obj->ring = ring; > > /* Add a reference if we're newly entering the active list. */ > -- > 1.8.3.2 > -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch