[PATCH v3 10/12] drm/udl: Fix inconsistent urbs.count value during udl_free_urb_list()

Takashi Iwai
2022-09-08T09:52:20Z

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().

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
drivers/gpu/drm/udl/udl_drv.h | 8 +------
drivers/gpu/drm/udl/udl_main.c | 42 +++++++++++++++++++++++-----------
2 files changed, 30 insertions(+), 20 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 de28eeff3155..16aa4a655e7f 100644
--- a/drivers/gpu/drm/udl/udl_main.c
+++ b/drivers/gpu/drm/udl/udl_main.c
@@ -23,6 +23,8 @@
#define WRITES_IN_FLIGHT (20)
#define MAX_VENDOR_DESCRIPTOR_SIZE 256

+static struct urb *udl_get_urb_locked(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);
@@ -146,15 +148,17 @@ 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_locked(udl, MAX_SCHEDULE_TIMEOUT);
+ udl->urbs.count--;
+ spin_unlock_irq(&udl->urbs.lock);
if (WARN_ON(!urb))
break;
unode = urb->context;
@@ -164,7 +168,8 @@ static void udl_free_urb_list(struct drm_device *dev)
usb_free_urb(urb);
kfree(unode);
}
- udl->urbs.count = 0;
+
+ wake_up_all(&udl->urbs.sleep);
}

static int udl_alloc_urb_list(struct drm_device *dev, int count, size_t size)
@@ -228,33 +233,44 @@ 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_locked(struct udl_device *udl, long timeout)
{
- struct udl_device *udl = to_udl(dev);
- struct urb_node *unode = NULL;
+ struct urb_node *unode;

- if (!udl->urbs.count)
- return NULL;
+ assert_spin_locked(&udl->urbs.lock);

/* 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,
+ !udl->urbs.count ||
!list_empty(&udl->urbs.list),
udl->urbs.lock, timeout)) {
DRM_INFO("wait for urb interrupted: available: %d\n",
udl->urbs.available);
- goto unlock;
+ return NULL;
}

+ if (!udl->urbs.count)
+ 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_locked(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);
--
2.35.3