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Thu, 26 Aug 2021 02:58:14 -0700 (PDT) Date: Thu, 26 Aug 2021 11:58:12 +0200 From: Daniel Vetter To: Desmond Cheong Zhi Xi Cc: maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@linux.ie, daniel@ffwll.ch, sumit.semwal@linaro.org, christian.koenig@amd.com, jani.nikula@linux.intel.com, joonas.lahtinen@linux.intel.com, rodrigo.vivi@intel.com, chris@chris-wilson.co.uk, ville.syrjala@linux.intel.com, matthew.auld@intel.com, dan.carpenter@oracle.com, tvrtko.ursulin@intel.com, matthew.d.roper@intel.com, lucas.demarchi@intel.com, karthik.b.s@intel.com, jose.souza@intel.com, manasi.d.navare@intel.com, airlied@redhat.com, aditya.swarup@intel.com, andrescj@chromium.org, linux-graphics-maintainer@vmware.com, zackr@vmware.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, skhan@linuxfoundation.org, gregkh@linuxfoundation.org, linux-kernel-mentees@lists.linuxfoundation.org Message-ID: Mail-Followup-To: Desmond Cheong Zhi Xi , maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@linux.ie, sumit.semwal@linaro.org, christian.koenig@amd.com, jani.nikula@linux.intel.com, joonas.lahtinen@linux.intel.com, rodrigo.vivi@intel.com, chris@chris-wilson.co.uk, ville.syrjala@linux.intel.com, matthew.auld@intel.com, dan.carpenter@oracle.com, tvrtko.ursulin@intel.com, matthew.d.roper@intel.com, lucas.demarchi@intel.com, karthik.b.s@intel.com, jose.souza@intel.com, manasi.d.navare@intel.com, airlied@redhat.com, aditya.swarup@intel.com, andrescj@chromium.org, linux-graphics-maintainer@vmware.com, zackr@vmware.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, skhan@linuxfoundation.org, gregkh@linuxfoundation.org, linux-kernel-mentees@lists.linuxfoundation.org References: <20210826020122.1488002-1-desmondcheongzx@gmail.com> <20210826020122.1488002-4-desmondcheongzx@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210826020122.1488002-4-desmondcheongzx@gmail.com> X-Operating-System: Linux phenom 5.10.0-7-amd64 Subject: Re: [Intel-gfx] [PATCH v8 3/7] drm: lock drm_global_mutex earlier in the ioctl handler 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: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Thu, Aug 26, 2021 at 10:01:18AM +0800, Desmond Cheong Zhi Xi wrote: > In a future patch, a read lock on drm_device.master_rwsem is > held in the ioctl handler before the check for ioctl > permissions. However, this inverts the lock hierarchy of > drm_global_mutex --> master_rwsem. > > To avoid this, we do some prep work to grab the drm_global_mutex > before checking for ioctl permissions. > > Signed-off-by: Desmond Cheong Zhi Xi > --- > drivers/gpu/drm/drm_ioctl.c | 18 +++++++++--------- > 1 file changed, 9 insertions(+), 9 deletions(-) > > diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c > index d25713b09b80..158629d88319 100644 > --- a/drivers/gpu/drm/drm_ioctl.c > +++ b/drivers/gpu/drm/drm_ioctl.c > @@ -772,19 +772,19 @@ long drm_ioctl_kernel(struct file *file, drm_ioctl_t *func, void *kdata, > if (drm_dev_is_unplugged(dev)) > return -ENODEV; > > + /* Enforce sane locking for modern driver ioctls. */ > + if (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)) && !(flags & DRM_UNLOCKED)) Maybe have a local bool locked_ioctl for this so it's extremely clear it's the same condition in both? Either way: Reviewed-by: Daniel Vetter > + mutex_lock(&drm_global_mutex); > + > retcode = drm_ioctl_permit(flags, file_priv); > if (unlikely(retcode)) > - return retcode; > + goto out; > > - /* Enforce sane locking for modern driver ioctls. */ > - if (likely(!drm_core_check_feature(dev, DRIVER_LEGACY)) || > - (flags & DRM_UNLOCKED)) > - retcode = func(dev, kdata, file_priv); > - else { > - mutex_lock(&drm_global_mutex); > - retcode = func(dev, kdata, file_priv); > + retcode = func(dev, kdata, file_priv); > + > +out: > + if (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)) && !(flags & DRM_UNLOCKED)) > mutex_unlock(&drm_global_mutex); > - } > return retcode; > } > EXPORT_SYMBOL(drm_ioctl_kernel); > -- > 2.25.1 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch