From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jani Nikula Subject: Re: [Intel-gfx] [PATCH] drm/i915: Fix context IDs not released on driver hot unbind Date: Thu, 04 Apr 2019 16:47:31 +0300 Message-ID: <87r2ahyj9o.fsf@intel.com> References: <20190404102445.12303-1-janusz.krzysztofik@linux.intel.com> <155437373474.7532.10868620123516507965@skylake-alporthouse-com> <155437462649.7532.18347010454266779928@skylake-alporthouse-com> <1bda752c136f3a75817fe257027edd8be4e7472e.camel@linux.intel.com> <155437522546.7532.6754257066058816161@skylake-alporthouse-com> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: <155437522546.7532.6754257066058816161@skylake-alporthouse-com> Sender: linux-kernel-owner@vger.kernel.org To: Chris Wilson , Janusz Krzysztofik Cc: David Airlie , intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Rodrigo Vivi List-Id: dri-devel@lists.freedesktop.org On Thu, 04 Apr 2019, Chris Wilson wrote: > Quoting Janusz Krzysztofik (2019-04-04 11:50:14) >> On Thu, 2019-04-04 at 11:43 +0100, Chris Wilson wrote: >> > Quoting Janusz Krzysztofik (2019-04-04 11:40:24) >> > > On Thu, 2019-04-04 at 11:28 +0100, Chris Wilson wrote: >> > > > Quoting Janusz Krzysztofik (2019-04-04 11:24:45) >> > > > > From: Janusz Krzysztofik >> > > > > >> > > > > In case the driver gets unbound while a device is open, kernel >> > > > > panic >> > > > > may be forced if a list of allocated context IDs is not empty. >> > > > > >> > > > > When a device is open, the list may happen to be not empty >> > > > > because >> > > > > a >> > > > > context ID, once allocated by a context ID allocator to a >> > > > > context >> > > > > assosiated with that open file descriptor, is released as late >> > > > > as >> > > > > on device close. >> > > > > >> > > > > On the other hand, there is a need to release all allocated >> > > > > context >> > > > > IDs >> > > > > and destroy the context ID allocator on driver unbind, even if >> > > > > a >> > > > > device >> > > > > is open, in order to free memory resources consumed and prevent >> > > > > from >> > > > > memory leaks. The purpose of the forced kernel panic was to >> > > > > protect >> > > > > the context ID allocator from being silently destroyed if not >> > > > > all >> > > > > allocated IDs had been released. >> > > > >> > > > Those open fd are still pointing into kernel memory where the >> > > > driver >> > > > used to be. The panic is entirely correct, we should not be >> > > > unloading >> > > > the module before those dangling pointers have been made safe. >> > > > >> > > > This is papering over the symptom. How is the module being >> > > > unloaded >> > > > with >> > > > open fd? >> > > >> > > A user can play with the driver unbind or device remove sysfs >> > > interface. >> > >> > Sure, but we must still follow all the steps before _unloading_ the >> > module or else the user is left pointing into reused kernel memory. >> >> I'm not talking about unloading the module, that is prevented by open >> fds. The driver still exists after being unbound from a device and may >> just respond with -ENODEV. > > i915_gem_contexts_fini() *is* module unload. Janusz, please describe what you're doing exactly. BR, Jani. -- Jani Nikula, Intel Open Source Graphics Center