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charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Subject: Re: [Intel-gfx] [PATCH] drm/i915: Fix NULL ptr deref by checking new_crtc_state X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: intel-gfx@lists.freedesktop.org Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Fri, May 05, 2023 at 03:09:01PM +0300, Ville Syrjälä wrote: > On Fri, May 05, 2023 at 02:41:24PM +0300, Lisovskiy, Stanislav wrote: > > On Fri, May 05, 2023 at 02:25:46PM +0300, Ville Syrjälä wrote: > > > On Fri, May 05, 2023 at 02:20:17PM +0300, Lisovskiy, Stanislav wrote: > > > > On Fri, May 05, 2023 at 02:06:34PM +0300, Ville Syrjälä wrote: > > > > > On Fri, May 05, 2023 at 02:05:27PM +0300, Lisovskiy, Stanislav wrote: > > > > > > On Fri, May 05, 2023 at 02:02:43PM +0300, Ville Syrjälä wrote: > > > > > > > On Fri, May 05, 2023 at 01:58:03PM +0300, Lisovskiy, Stanislav wrote: > > > > > > > > On Fri, May 05, 2023 at 01:54:14PM +0300, Ville Syrjälä wrote: > > > > > > > > > On Fri, May 05, 2023 at 11:22:12AM +0300, Stanislav Lisovskiy wrote: > > > > > > > > > > intel_atomic_get_new_crtc_state can return NULL, unless crtc state wasn't > > > > > > > > > > obtained previously with intel_atomic_get_crtc_state, so we must check it > > > > > > > > > > for NULLness here, just as in many other places, where we can't guarantee > > > > > > > > > > that intel_atomic_get_crtc_state was called. > > > > > > > > > > We are currently getting NULL ptr deref because of that, so this fix was > > > > > > > > > > confirmed to help. > > > > > > > > > > > > > > > > > > > > Fixes: 74a75dc90869 ("drm/i915/display: move plane prepare/cleanup to intel_atomic_plane.c") > > > > > > > > > > Signed-off-by: Stanislav Lisovskiy > > > > > > > > > > --- > > > > > > > > > > drivers/gpu/drm/i915/display/intel_atomic_plane.c | 4 ++-- > > > > > > > > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > > > > > > > > > > > > > > > diff --git a/drivers/gpu/drm/i915/display/intel_atomic_plane.c b/drivers/gpu/drm/i915/display/intel_atomic_plane.c > > > > > > > > > > index 9f670dcfe76e..4125ee07a271 100644 > > > > > > > > > > --- a/drivers/gpu/drm/i915/display/intel_atomic_plane.c > > > > > > > > > > +++ b/drivers/gpu/drm/i915/display/intel_atomic_plane.c > > > > > > > > > > @@ -1029,7 +1029,7 @@ intel_prepare_plane_fb(struct drm_plane *_plane, > > > > > > > > > > int ret; > > > > > > > > > > > > > > > > > > > > if (old_obj) { > > > > > > > > > > - const struct intel_crtc_state *crtc_state = > > > > > > > > > > + const struct intel_crtc_state *new_crtc_state = > > > > > > > > > > intel_atomic_get_new_crtc_state(state, > > > > > > > > > > to_intel_crtc(old_plane_state->hw.crtc)); > > > > > > > > > > > > > > > > > > > > @@ -1044,7 +1044,7 @@ intel_prepare_plane_fb(struct drm_plane *_plane, > > > > > > > > > > * This should only fail upon a hung GPU, in which case we > > > > > > > > > > * can safely continue. > > > > > > > > > > */ > > > > > > > > > > - if (intel_crtc_needs_modeset(crtc_state)) { > > > > > > > > > > + if (new_crtc_state && intel_crtc_needs_modeset(new_crtc_state)) { > > > > > > > > > > > > > > > > > > NAK. We need to fix the bug instead of paparing over it. > > > > > > > > > > > > > > > > I had pushed this already. > > > > > > > > > > > > > > It didn't even finish CI. Please revert. > > > > > > > > > > > > Swati did run CI and verified that fix helps. I'm _not_ going to revert. > > > > > > > > > > Fine. I'll do it. > > > > > > > > Problem is that you don't even care to explain, why this fix is wrong, but simply > > > > act in authoritarian way, instead of having constructive discussion. > > > > > > I've explanined this one about a hundred times. The NULL pointer should > > > not happen. Someone needs to actually analyze what is happening instead > > > of just adding randomg NULL checks all over the place. > > > > I do get this point. However why are we doing those check in other places then? > > We do then when they are actually necessary. Well but for example when we do check like if(new_bw_state) in intel_bw.c, we are also might be having potentially some silent bugs. Would you guarantee that if we remove all if(crtc_state) and if(new_bw_state) checks in our code, that there won't be NULL pointer dereferences? I bet you don't. But IF you do, then lets remove it everywhere then, why keeping it there, if we are sure! :)) > > > Moreover I can remember that you told me to do this check even, when were reviewing > > my other patches. Because we always have to check result of this function, as it > > can be NULL, in case if intel_atomic_get_crtc_state wasn't called before, which > > could happen even in normal case, as I understand. > > You can't apply that kind of general rule. Whether the crtc should have > already been added to the state or not is case dependent. In this case > that should never be the case since the plane was already added to the > state, and thus its crtc should also have been added. Well it is kinda weird, that we don't have clear rules here. As I understand this is Bigjoiner, so most likely that was the reason why intel_get_crtc_state wasn't called. I mean I was anyway planning to continue investigating that Bigjoiner logic here in fact, however that fix could help at least CI team to continue testing further. > > > > > If we want to understand why it happens in particular here, great lets investigate, > > however I don't get why we are having same checks everywhere all over the place then > > and I can even find your words, that we need to do those checks as well. > > > > Also if this doesn't break anything, > > You can't know that. You're trading a clearly reproducible > bug with a silent bug that can cause who knows what other > issues. That one will be impossible to debug. Answered above... > > > improves our CI results, not violating our coding > > practices, because once again worth mentioning we do check new_crtc_state for NULLness > > in many places.. then why it can't be the fix? > > If we find better solution thats great, but there are plenty of other things as well, > > if you haven't noticed. > > > > Can we somehow _stop_ these childish kindergarden level review arguing warfare, at least > > for sake of professional efficiency? > > Not sure what that kindergarten level stuff is. I just > NAKed the patch. Well, I'm glad, we are at least discussing now, why you NAKed it, initially without having discussion first. > > > > > For all my next patches I will always add you to CC and _personally_ will ask to review, > > even though quite often when I do this - I get nothing. > > I can't review everything in detail. But in any case you should > at least wait a day or two for review feedback, and you definitely > need to wait for CI results as well. Sometimes I wait for weeks. > > -- > Ville Syrjälä > Intel