On Wed, Jan 29, 2020 at 05:47:33PM +0100, Sam Ravnborg wrote: > Hi Daniel. > > In the nit-pick department today - sorry. > > Subject: [PATCH 5/5] drm: Nerv drm_global_mutex BKL for good drivers > I did not understand this subject... - what is "Nerv"? It's a typo, supposed to be nerf: https://www.urbandictionary.com/define.php?term=nerf Cheers, Daniel > > Sam > > On Wed, Jan 29, 2020 at 09:24:10AM +0100, Daniel Vetter wrote: > > This catches the majority of drivers (unfortunately not if we take > > users into account, because all the big drivers have at least a > > lastclose hook). > > > > With the prep patches out of the way all drm state is fully protected > > and either prevents or can deal with the races from dropping the BKL > > around open/close. The only thing left to audit are the various driver > > hooks - by keeping the BKL around if any of them are set we have a > > very simple cop-out! > > > > Note that one of the biggest prep pieces to get here was making > > dev->open_count atomic, which was done in > > > > commit 7e13ad896484a0165a68197a2e64091ea28c9602 > > Author: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > Date: Fri Jan 24 13:01:07 2020 +0000 > > > > drm: Avoid drm_global_mutex for simple inc/dec of dev->open_count > > > > Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> > > --- > > drivers/gpu/drm/drm_drv.c | 6 +++-- > > drivers/gpu/drm/drm_file.c | 46 ++++++++++++++++++++++++++++++---- > > drivers/gpu/drm/drm_internal.h | 1 + > > 3 files changed, 46 insertions(+), 7 deletions(-) > > > > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c > > index 05bdf0b9d2b3..9fcd6ab3c154 100644 > > --- a/drivers/gpu/drm/drm_drv.c > > +++ b/drivers/gpu/drm/drm_drv.c > > @@ -946,7 +946,8 @@ int drm_dev_register(struct drm_device *dev, unsigned long flags) > > struct drm_driver *driver = dev->driver; > > int ret; > > > > - mutex_lock(&drm_global_mutex); > > + if (drm_dev_needs_global_mutex(dev)) > > + mutex_lock(&drm_global_mutex); > > > > if (dev->driver->load) { > > if (!drm_core_check_feature(dev, DRIVER_LEGACY)) > > @@ -992,7 +993,8 @@ int drm_dev_register(struct drm_device *dev, unsigned long flags) > > drm_minor_unregister(dev, DRM_MINOR_PRIMARY); > > drm_minor_unregister(dev, DRM_MINOR_RENDER); > > out_unlock: > > - mutex_unlock(&drm_global_mutex); > > + if (drm_dev_needs_global_mutex(dev)) > > + mutex_unlock(&drm_global_mutex); > > return ret; > > } > > EXPORT_SYMBOL(drm_dev_register); > > diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c > > index d36cb74ebe0c..efd6fe0b6b4f 100644 > > --- a/drivers/gpu/drm/drm_file.c > > +++ b/drivers/gpu/drm/drm_file.c > > @@ -51,6 +51,37 @@ > > /* from BKL pushdown */ > > DEFINE_MUTEX(drm_global_mutex); > > > > +bool drm_dev_needs_global_mutex(struct drm_device *dev) > > +{ > > + /* > > + * Legacy drivers rely on all kinds of BKL locking semantics, don't > > + * bother. They also still need BKL locking for their ioctls, so better > > + * safe than sorry. > > + */ > > + if (drm_core_check_feature(dev, DRIVER_LEGACY)) > > + return true; > > + > > + /* > > + * The deprecated ->load callback must be called after the driver is > > + * already registered. This means such drivers rely on the BKL to make > > + * sure an open can't proceed until the driver is actually fully set up. > > + * Similar hilarity holds for the unload callback. > > + */ > > + if (dev->driver->load || dev->driver->unload) > > + return true; > > + > > + /* > > + * Drivers with the lastclose callback assume that it's synchronized > > + * against concurrent opens, which again needs the BKL. The proper fix > > + * is to use the drm_client infrastructure with proper locking for each > > + * client. > > + */ > > + if (dev->driver->lastclose) > > + return true; > > + > > + return false; > > +} > > + > > /** > > * DOC: file operations > > * > > @@ -378,9 +409,10 @@ int drm_open(struct inode *inode, struct file *filp) > > if (IS_ERR(minor)) > > return PTR_ERR(minor); > > > > - mutex_unlock(&drm_global_mutex); > > - > > dev = minor->dev; > > + if (drm_dev_needs_global_mutex(dev)) > > + mutex_unlock(&drm_global_mutex); > > + > > if (!atomic_fetch_inc(&dev->open_count)) > > need_setup = 1; > > > > @@ -398,13 +430,15 @@ int drm_open(struct inode *inode, struct file *filp) > > } > > } > > > > - mutex_unlock(&drm_global_mutex); > > + if (drm_dev_needs_global_mutex(dev)) > > + mutex_unlock(&drm_global_mutex); > > > > return 0; > > > > err_undo: > > atomic_dec(&dev->open_count); > > - mutex_unlock(&drm_global_mutex); > > + if (drm_dev_needs_global_mutex(dev)) > > + mutex_unlock(&drm_global_mutex); > > drm_minor_release(minor); > > return retcode; > > } > > @@ -444,6 +478,7 @@ int drm_release(struct inode *inode, struct file *filp) > > struct drm_minor *minor = file_priv->minor; > > struct drm_device *dev = minor->dev; > > > > + if (drm_dev_needs_global_mutex(dev)) > > mutex_lock(&drm_global_mutex); > > > > DRM_DEBUG("open_count = %d\n", atomic_read(&dev->open_count)); > > @@ -453,7 +488,8 @@ int drm_release(struct inode *inode, struct file *filp) > > if (atomic_dec_and_test(&dev->open_count)) > > drm_lastclose(dev); > > > > - mutex_unlock(&drm_global_mutex); > > + if (drm_dev_needs_global_mutex(dev)) > > + mutex_unlock(&drm_global_mutex); > > > > drm_minor_release(minor); > > > > diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h > > index 6937bf923f05..aeec2e68d772 100644 > > --- a/drivers/gpu/drm/drm_internal.h > > +++ b/drivers/gpu/drm/drm_internal.h > > @@ -41,6 +41,7 @@ struct drm_printer; > > > > /* drm_file.c */ > > extern struct mutex drm_global_mutex; > > +bool drm_dev_needs_global_mutex(struct drm_device *dev); > > struct drm_file *drm_file_alloc(struct drm_minor *minor); > > void drm_file_free(struct drm_file *file); > > void drm_lastclose(struct drm_device *dev); > > -- > > 2.24.1 > > > > _______________________________________________ > > dri-devel mailing list > > dri-devel@xxxxxxxxxxxxxxxxxxxxx > > https://lists.freedesktop.org/mailman/listinfo/dri-devel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
