Messages in this thread | | | Date | Mon, 5 Sep 2022 10:32:55 +0200 | Subject | Re: [PATCH 10/12] drm/udl: Fix inconsistent urbs.count value during udl_free_urb_list() | From | Thomas Zimmermann <> |
| |
Hi
Am 16.08.22 um 17:36 schrieb Takashi Iwai: > In the current design, udl_get_urb() may be called asynchronously > during the driver freeing its URL list via udl_free_urb_list(). > The problem is that the sync is determined by comparing the urbs.count > and urbs.available fields, while we clear urbs.count field only once > after udl_free_urb_list() finishes, i.e. during udl_free_urb_list(), > the state becomes inconsistent. > > For fixing this inconsistency and also for hardening the locking > scheme, this patch does a slight refactoring of the code around > udl_get_urb() and udl_free_urb_list(). Now urbs.count is updated in > the same spinlock at extracting a URB from the list in > udl_free_url_list(). > > Signed-off-by: Takashi Iwai <tiwai@suse.de> > --- > drivers/gpu/drm/udl/udl_drv.h | 8 +------- > drivers/gpu/drm/udl/udl_main.c | 37 ++++++++++++++++++++++++---------- > 2 files changed, 27 insertions(+), 18 deletions(-) > > diff --git a/drivers/gpu/drm/udl/udl_drv.h b/drivers/gpu/drm/udl/udl_drv.h > index 5923d2e02bc8..d943684b5bbb 100644 > --- a/drivers/gpu/drm/udl/udl_drv.h > +++ b/drivers/gpu/drm/udl/udl_drv.h > @@ -74,13 +74,7 @@ static inline struct usb_device *udl_to_usb_device(struct udl_device *udl) > int udl_modeset_init(struct drm_device *dev); > struct drm_connector *udl_connector_init(struct drm_device *dev); > > -struct urb *udl_get_urb_timeout(struct drm_device *dev, long timeout); > - > -#define GET_URB_TIMEOUT HZ > -static inline struct urb *udl_get_urb(struct drm_device *dev) > -{ > - return udl_get_urb_timeout(dev, GET_URB_TIMEOUT); > -} > +struct urb *udl_get_urb(struct drm_device *dev); > > int udl_submit_urb(struct drm_device *dev, struct urb *urb, size_t len); > int udl_sync_pending_urbs(struct drm_device *dev); > diff --git a/drivers/gpu/drm/udl/udl_main.c b/drivers/gpu/drm/udl/udl_main.c > index 8bbb4e2861fb..19dc8317e843 100644 > --- a/drivers/gpu/drm/udl/udl_main.c > +++ b/drivers/gpu/drm/udl/udl_main.c > @@ -28,6 +28,8 @@ > static uint udl_num_urbs = WRITES_IN_FLIGHT; > module_param_named(numurbs, udl_num_urbs, uint, 0600); > > +static struct urb *__udl_get_urb(struct udl_device *udl, long timeout); > + > static int udl_parse_vendor_descriptor(struct udl_device *udl) > { > struct usb_device *udev = udl_to_usb_device(udl); > @@ -151,15 +153,17 @@ void udl_urb_completion(struct urb *urb) > static void udl_free_urb_list(struct drm_device *dev) > { > struct udl_device *udl = to_udl(dev); > - int count = udl->urbs.count; > struct urb_node *unode; > struct urb *urb; > > DRM_DEBUG("Waiting for completes and freeing all render urbs\n"); > > /* keep waiting and freeing, until we've got 'em all */ > - while (count--) { > - urb = udl_get_urb_timeout(dev, MAX_SCHEDULE_TIMEOUT); > + while (udl->urbs.count) { > + spin_lock_irq(&udl->urbs.lock); > + urb = __udl_get_urb(udl, MAX_SCHEDULE_TIMEOUT); > + udl->urbs.count--; > + spin_unlock_irq(&udl->urbs.lock); > if (WARN_ON(!urb)) > break; > unode = urb->context; > @@ -169,7 +173,8 @@ static void udl_free_urb_list(struct drm_device *dev) > usb_free_urb(urb); > kfree(unode); > } > - udl->urbs.count = 0; > + > + wake_up(&udl->urbs.sleep);
There's just one waiter, but it's the shutdown code. Maybe wake_up_all() would more clearly communicate the intention.
> } > > static int udl_alloc_urb_list(struct drm_device *dev, int count, size_t size) > @@ -233,33 +238,43 @@ static int udl_alloc_urb_list(struct drm_device *dev, int count, size_t size) > return udl->urbs.count; > } > > -struct urb *udl_get_urb_timeout(struct drm_device *dev, long timeout) > +static struct urb *__udl_get_urb(struct udl_device *udl, long timeout)
I think in DRM, the correct name for this function would be udl_get_urb_locked().
> { > - struct udl_device *udl = to_udl(dev); > - struct urb_node *unode = NULL; > + struct urb_node *unode; > + > + assert_spin_locked(&udl->urbs.lock); > > if (!udl->urbs.count) > return NULL; > > /* Wait for an in-flight buffer to complete and get re-queued */ > - spin_lock_irq(&udl->urbs.lock); > if (!wait_event_lock_irq_timeout(udl->urbs.sleep, > !list_empty(&udl->urbs.list),
The urb-free function will wake up this code, but the urb list should be empty then. Should we update the condition to something like 'udl->urbs.count && !list_empty()' ?
Best regards Thomas
> udl->urbs.lock, timeout)) { > DRM_INFO("wait for urb interrupted: available: %d\n", > udl->urbs.available); > - goto unlock; > + return NULL; > } > > unode = list_first_entry(&udl->urbs.list, struct urb_node, entry); > list_del_init(&unode->entry); > udl->urbs.available--; > > -unlock: > - spin_unlock_irq(&udl->urbs.lock); > return unode ? unode->urb : NULL; > } > > +#define GET_URB_TIMEOUT HZ > +struct urb *udl_get_urb(struct drm_device *dev) > +{ > + struct udl_device *udl = to_udl(dev); > + struct urb *urb; > + > + spin_lock_irq(&udl->urbs.lock); > + urb = __udl_get_urb(udl, GET_URB_TIMEOUT); > + spin_unlock_irq(&udl->urbs.lock); > + return urb; > +} > + > int udl_submit_urb(struct drm_device *dev, struct urb *urb, size_t len) > { > struct udl_device *udl = to_udl(dev);
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Ivo Totev [unhandled content-type:application/pgp-signature] | |