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[212.51.149.96]) by smtp.gmail.com with ESMTPSA id f36sm3799428ede.28.2019.10.08.02.50.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Oct 2019 02:50:35 -0700 (PDT) Date: Tue, 8 Oct 2019 11:50:33 +0200 From: Daniel Vetter To: Sean Paul Cc: Daniel Vetter , dri-devel , Sean Paul , Rob Clark , Deepak Rawat , Thomas Hellstrom , Maarten Lankhorst , Maxime Ripard , David Airlie , stable Subject: Re: [PATCH] drm: damage_helper: Fix race checking plane->state->fb Message-ID: <20191008095033.GJ16989@phenom.ffwll.local> References: <20190904202938.110207-1-sean@poorly.run> <20190919150401.GV218215@art_vandelay> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190919150401.GV218215@art_vandelay> X-Operating-System: Linux phenom 5.2.0-2-amd64 User-Agent: Mutt/1.10.1 (2018-07-13) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Thu, Sep 19, 2019 at 11:04:01AM -0400, Sean Paul wrote: > On Thu, Sep 05, 2019 at 12:41:27PM +0200, Daniel Vetter wrote: > > On Wed, Sep 4, 2019 at 10:29 PM Sean Paul wrote: > > > > > > From: Sean Paul > > > > > > Since the dirtyfb ioctl doesn't give us any hints as to which plane is > > > scanning out the fb it's marking as damaged, we need to loop through > > > planes to find it. > > > > > > Currently we just reach into plane state and check, but that can race > > > with another commit changing the fb out from under us. This patch locks > > > the plane before checking the fb and will release the lock if the plane > > > is not displaying the dirty fb. > > > > > > Fixes: b9fc5e01d1ce ("drm: Add helper to implement legacy dirtyfb") > > > Cc: Rob Clark > > > Cc: Deepak Rawat > > > Cc: Daniel Vetter > > > Cc: Thomas Hellstrom > > > Cc: Maarten Lankhorst > > > Cc: Maxime Ripard > > > Cc: Sean Paul > > > Cc: David Airlie > > > Cc: Daniel Vetter > > > Cc: dri-devel@lists.freedesktop.org > > > Cc: # v5.0+ > > > Reported-by: Daniel Vetter > > > Signed-off-by: Sean Paul > > > --- > > > drivers/gpu/drm/drm_damage_helper.c | 8 +++++++- > > > 1 file changed, 7 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/gpu/drm/drm_damage_helper.c b/drivers/gpu/drm/drm_damage_helper.c > > > index 8230dac01a89..3a4126dc2520 100644 > > > --- a/drivers/gpu/drm/drm_damage_helper.c > > > +++ b/drivers/gpu/drm/drm_damage_helper.c > > > @@ -212,8 +212,14 @@ int drm_atomic_helper_dirtyfb(struct drm_framebuffer *fb, > > > drm_for_each_plane(plane, fb->dev) { > > > struct drm_plane_state *plane_state; > > > > > > - if (plane->state->fb != fb) > > > + ret = drm_modeset_lock(&plane->mutex, state->acquire_ctx); > > > + if (ret) > > > > I think for paranoid safety we should have a WARN_ON(ret == -EALREADY) > > here. It should be impossible, but if it's not for some oddball > > reason, we'll blow up. > > drm_modeset_lock eats EALREADY and returns 0 for that case, so I guess it > depends _how_ paranoid you want to be here :-) Ah silly me, r-b as-is then. -Daniel > > > > > With that: Reviewed-by: Daniel Vetter > > > > But please give this a spin with some workloads and the ww_mutex > > slowpath debugging enabled, just to makre sure. > > Ok, had a chance to run through some tests this morning with > CONFIG_DEBUG_WW_MUTEX_SLOWPATH and things lgtm > > Sean > > > -Daniel > > > > > + goto out; > > > + > > > + if (plane->state->fb != fb) { > > > + drm_modeset_unlock(&plane->mutex); > > > continue; > > > + } > > > > > > plane_state = drm_atomic_get_plane_state(state, plane); > > > if (IS_ERR(plane_state)) { > > > -- > > > Sean Paul, Software Engineer, Google / Chromium OS > > > > > > > > > -- > > Daniel Vetter > > Software Engineer, Intel Corporation > > +41 (0) 79 365 57 48 - http://blog.ffwll.ch > > -- > Sean Paul, Software Engineer, Google / Chromium OS -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch