[PATCH v2] usbip: give back URBs for unsent unlink requests during cleanup

In vhci_device_unlink_cleanup(), the URBs for unsent unlink requests are
not given back. This sometimes causes usb_kill_urb to wait indefinitely
for that urb to be given back. syzbot has reported a hung task issue [1]
for this.

To fix this, give back the urbs corresponding to unsent unlink requests
(unlink_tx list) similar to how urbs corresponding to unanswered unlink
requests (unlink_rx list) are given back. Since the code is almost the
same, extract it into a new function and call it for both unlink_rx and
unlink_tx lists.

[1]: https://syzkaller.appspot.com/bug?id=08f12df95ae7da69814e64eb5515d5a85ed06b76

Reported-by: syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com
Tested-by: syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com
Signed-off-by: Anirudh Rayabharam <redacted>
---

Changes in v2:
Use WARN_ON() instead of BUG() when unlink_list is neither unlink_tx nor
unlink_rx.

v1: https://lore.kernel.org/lkml/20210806164015.25263-1-mail@anirudhrb.com/

---
 drivers/usb/usbip/vhci_hcd.c | 45 +++++++++++++++++++++++++-----------
 1 file changed, 32 insertions(+), 13 deletions(-)

diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
index 4ba6bcdaa8e9..67e638f4c455 100644
--- a/drivers/usb/usbip/vhci_hcd.c
+++ b/drivers/usb/usbip/vhci_hcd.c

@@ -945,7 +945,8 @@ static int vhci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
 	return 0;
 }
 
-static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
+static void __vhci_cleanup_unlink_list(struct vhci_device *vdev,
+		struct list_head *unlink_list)
 {
 	struct vhci_hcd *vhci_hcd = vdev_to_vhci_hcd(vdev);
 	struct usb_hcd *hcd = vhci_hcd_to_hcd(vhci_hcd);

@@ -953,23 +954,23 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
 	struct vhci_unlink *unlink, *tmp;
 	unsigned long flags;
 
+	if (WARN(unlink_list != &vdev->unlink_tx
+				&& unlink_list != &vdev->unlink_rx,
+			"Invalid list passed to __vhci_cleanup_unlink_list\n"))
+		return;
+
 	spin_lock_irqsave(&vhci->lock, flags);
 	spin_lock(&vdev->priv_lock);
 
-	list_for_each_entry_safe(unlink, tmp, &vdev->unlink_tx, list) {
-		pr_info("unlink cleanup tx %lu\n", unlink->unlink_seqnum);
-		list_del(&unlink->list);
-		kfree(unlink);
-	}
-
-	while (!list_empty(&vdev->unlink_rx)) {
+	list_for_each_entry_safe(unlink, tmp, unlink_list, list) {
 		struct urb *urb;
 
-		unlink = list_first_entry(&vdev->unlink_rx, struct vhci_unlink,
-			list);
-
-		/* give back URB of unanswered unlink request */
-		pr_info("unlink cleanup rx %lu\n", unlink->unlink_seqnum);
+		if (unlink_list == &vdev->unlink_tx)
+			pr_info("unlink cleanup tx %lu\n",
+					unlink->unlink_seqnum);
+		else
+			pr_info("unlink cleanup rx %lu\n",
+					unlink->unlink_seqnum);
 
 		urb = pickup_urb_and_free_priv(vdev, unlink->unlink_seqnum);
 		if (!urb) {

@@ -1001,6 +1002,24 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
 	spin_unlock_irqrestore(&vhci->lock, flags);
 }
 
+static inline void vhci_cleanup_unlink_tx(struct vhci_device *vdev)
+{
+	__vhci_cleanup_unlink_list(vdev, &vdev->unlink_tx);
+}
+
+static inline void vhci_cleanup_unlink_rx(struct vhci_device *vdev)
+{
+	__vhci_cleanup_unlink_list(vdev, &vdev->unlink_rx);
+}
+
+static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
+{
+	/* give back URBs of unsent unlink requests */
+	vhci_cleanup_unlink_tx(vdev);
+	/* give back URBs of unanswered unlink requests */
+	vhci_cleanup_unlink_rx(vdev);
+}
+
 /*
  * The important thing is that only one context begins cleanup.
  * This is why error handling and cleanup become simple.

-- 
2.26.2

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On 8/6/21 12:13 PM, Anirudh Rayabharam wrote:

In vhci_device_unlink_cleanup(), the URBs for unsent unlink requests are
not given back. This sometimes causes usb_kill_urb to wait indefinitely
for that urb to be given back. syzbot has reported a hung task issue [1]
for this.

To fix this, give back the urbs corresponding to unsent unlink requests
(unlink_tx list) similar to how urbs corresponding to unanswered unlink
requests (unlink_rx list) are given back. Since the code is almost the
same, extract it into a new function and call it for both unlink_rx and
unlink_tx lists.

Let's not do the refactor - let's first fix the problem and then the refactor.

With this change, this will be only place unlink_rx is used without
vdev->priv_lock hold? Please explain why this is safe.

With this change, this will be only place unlink_rx is used without
vdev->priv_lock hold? Please explain why this is safe.

+}
+

Is there a need for this layer?

With this change, this will be only place unlink_rx is used without
vdev->priv_lock hold? Please explain why this is safe.

+}
+

Is there a need for this layer?

thanks,
-- Shuah
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On Tue, Aug 10, 2021 at 05:25:51PM -0600, Shuah Khan wrote:

On 8/6/21 12:13 PM, Anirudh Rayabharam wrote:

quoted

In vhci_device_unlink_cleanup(), the URBs for unsent unlink requests are
not given back. This sometimes causes usb_kill_urb to wait indefinitely
for that urb to be given back. syzbot has reported a hung task issue [1]
for this.

To fix this, give back the urbs corresponding to unsent unlink requests
(unlink_tx list) similar to how urbs corresponding to unanswered unlink
requests (unlink_rx list) are given back. Since the code is almost the
same, extract it into a new function and call it for both unlink_rx and
unlink_tx lists.

Let's not do the refactor - let's first fix the problem and then the refactor.

Sure, I will make it a two patch series where the first one fixes the
problem and the second one does the refactor.

quoted

[1]: https://syzkaller.appspot.com/bug?id=08f12df95ae7da69814e64eb5515d5a85ed06b76

Reported-by: syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com
Tested-by: syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com
Signed-off-by: Anirudh Rayabharam <redacted>
---

Changes in v2:
Use WARN_ON() instead of BUG() when unlink_list is neither unlink_tx nor
unlink_rx.

v1: https://lore.kernel.org/lkml/20210806164015.25263-1-mail@anirudhrb.com/

---
  drivers/usb/usbip/vhci_hcd.c | 45 +++++++++++++++++++++++++-----------
  1 file changed, 32 insertions(+), 13 deletions(-)

diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
index 4ba6bcdaa8e9..67e638f4c455 100644
--- a/drivers/usb/usbip/vhci_hcd.c
+++ b/drivers/usb/usbip/vhci_hcd.c

@@ -945,7 +945,8 @@ static int vhci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
  	return 0;
  }
-static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
+static void __vhci_cleanup_unlink_list(struct vhci_device *vdev,
+		struct list_head *unlink_list)
  {
  	struct vhci_hcd *vhci_hcd = vdev_to_vhci_hcd(vdev);
  	struct usb_hcd *hcd = vhci_hcd_to_hcd(vhci_hcd);

@@ -953,23 +954,23 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
  	struct vhci_unlink *unlink, *tmp;
  	unsigned long flags;
+	if (WARN(unlink_list != &vdev->unlink_tx
+				&& unlink_list != &vdev->unlink_rx,
+			"Invalid list passed to __vhci_cleanup_unlink_list\n"))
+		return;
+

With this change, this will be only place unlink_rx is used without
vdev->priv_lock hold? Please explain why this is safe.

Well, this doesn't read or modify the contents of unlink_rx and unlink_tx.
So, it looks safe to me. Let me know if I'm missing something here.

quoted

  	spin_lock_irqsave(&vhci->lock, flags);
  	spin_lock(&vdev->priv_lock);
-	list_for_each_entry_safe(unlink, tmp, &vdev->unlink_tx, list) {
-		pr_info("unlink cleanup tx %lu\n", unlink->unlink_seqnum);
-		list_del(&unlink->list);
-		kfree(unlink);
-	}
-
-	while (!list_empty(&vdev->unlink_rx)) {
+	list_for_each_entry_safe(unlink, tmp, unlink_list, list) {
  		struct urb *urb;
-		unlink = list_first_entry(&vdev->unlink_rx, struct vhci_unlink,
-			list);
-
-		/* give back URB of unanswered unlink request */
-		pr_info("unlink cleanup rx %lu\n", unlink->unlink_seqnum);
+		if (unlink_list == &vdev->unlink_tx)
+			pr_info("unlink cleanup tx %lu\n",
+					unlink->unlink_seqnum);
+		else
+			pr_info("unlink cleanup rx %lu\n",
+					unlink->unlink_seqnum);
  		urb = pickup_urb_and_free_priv(vdev, unlink->unlink_seqnum);
  		if (!urb) {

@@ -1001,6 +1002,24 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
  	spin_unlock_irqrestore(&vhci->lock, flags);
  }
+static inline void vhci_cleanup_unlink_tx(struct vhci_device *vdev)
+{
+	__vhci_cleanup_unlink_list(vdev, &vdev->unlink_tx);

With this change, this will be only place unlink_rx is used without
vdev->priv_lock hold? Please explain why this is safe.

quoted

+}
+

Is there a need for this layer?

quoted

+static inline void vhci_cleanup_unlink_rx(struct vhci_device *vdev)
+{
+	__vhci_cleanup_unlink_list(vdev, &vdev->unlink_rx);

With this change, this will be only place unlink_rx is used without
vdev->priv_lock hold? Please explain why this is safe.

quoted

+}
+

Is there a need for this layer?

I added these wrappers purely for convenience. There is no other purpose.
Would you prefer this patch without the wrappers?

Thanks for the review!

	- Anirudh.
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On 8/11/21 7:58 AM, Anirudh Rayabharam wrote:

On Tue, Aug 10, 2021 at 05:25:51PM -0600, Shuah Khan wrote:

quoted

On 8/6/21 12:13 PM, Anirudh Rayabharam wrote:

quoted

In vhci_device_unlink_cleanup(), the URBs for unsent unlink requests are
not given back. This sometimes causes usb_kill_urb to wait indefinitely
for that urb to be given back. syzbot has reported a hung task issue [1]
for this.

To fix this, give back the urbs corresponding to unsent unlink requests
(unlink_tx list) similar to how urbs corresponding to unanswered unlink
requests (unlink_rx list) are given back. Since the code is almost the
same, extract it into a new function and call it for both unlink_rx and
unlink_tx lists.

Let's not do the refactor - let's first fix the problem and then the refactor.

Sure, I will make it a two patch series where the first one fixes the
problem and the second one does the refactor.

quoted

quoted

[1]: https://syzkaller.appspot.com/bug?id=08f12df95ae7da69814e64eb5515d5a85ed06b76

Reported-by: syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com
Tested-by: syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com
Signed-off-by: Anirudh Rayabharam <redacted>
---

Changes in v2:
Use WARN_ON() instead of BUG() when unlink_list is neither unlink_tx nor
unlink_rx.

v1: https://lore.kernel.org/lkml/20210806164015.25263-1-mail@anirudhrb.com/

---
   drivers/usb/usbip/vhci_hcd.c | 45 +++++++++++++++++++++++++-----------
   1 file changed, 32 insertions(+), 13 deletions(-)

diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
index 4ba6bcdaa8e9..67e638f4c455 100644
--- a/drivers/usb/usbip/vhci_hcd.c
+++ b/drivers/usb/usbip/vhci_hcd.c

@@ -945,7 +945,8 @@ static int vhci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
   	return 0;
   }
-static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
+static void __vhci_cleanup_unlink_list(struct vhci_device *vdev,
+		struct list_head *unlink_list)
   {
   	struct vhci_hcd *vhci_hcd = vdev_to_vhci_hcd(vdev);
   	struct usb_hcd *hcd = vhci_hcd_to_hcd(vhci_hcd);

@@ -953,23 +954,23 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
   	struct vhci_unlink *unlink, *tmp;
   	unsigned long flags;
+	if (WARN(unlink_list != &vdev->unlink_tx
+				&& unlink_list != &vdev->unlink_rx,
+			"Invalid list passed to __vhci_cleanup_unlink_list\n"))
+		return;
+

With this change, this will be only place unlink_rx is used without
vdev->priv_lock hold? Please explain why this is safe.

Well, this doesn't read or modify the contents of unlink_rx and unlink_tx.
So, it looks safe to me. Let me know if I'm missing something here.

quoted

quoted

   	spin_lock_irqsave(&vhci->lock, flags);
   	spin_lock(&vdev->priv_lock);
-	list_for_each_entry_safe(unlink, tmp, &vdev->unlink_tx, list) {
-		pr_info("unlink cleanup tx %lu\n", unlink->unlink_seqnum);
-		list_del(&unlink->list);
-		kfree(unlink);
-	}
-
-	while (!list_empty(&vdev->unlink_rx)) {
+	list_for_each_entry_safe(unlink, tmp, unlink_list, list) {
   		struct urb *urb;
-		unlink = list_first_entry(&vdev->unlink_rx, struct vhci_unlink,
-			list);
-
-		/* give back URB of unanswered unlink request */
-		pr_info("unlink cleanup rx %lu\n", unlink->unlink_seqnum);
+		if (unlink_list == &vdev->unlink_tx)
+			pr_info("unlink cleanup tx %lu\n",
+					unlink->unlink_seqnum);
+		else
+			pr_info("unlink cleanup rx %lu\n",
+					unlink->unlink_seqnum);
   		urb = pickup_urb_and_free_priv(vdev, unlink->unlink_seqnum);
   		if (!urb) {

@@ -1001,6 +1002,24 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
   	spin_unlock_irqrestore(&vhci->lock, flags);
   }
+static inline void vhci_cleanup_unlink_tx(struct vhci_device *vdev)
+{
+	__vhci_cleanup_unlink_list(vdev, &vdev->unlink_tx);

With this change, this will be only place unlink_rx is used without
vdev->priv_lock hold? Please explain why this is safe.

quoted

+}
+

Is there a need for this layer?

quoted

+static inline void vhci_cleanup_unlink_rx(struct vhci_device *vdev)
+{
+	__vhci_cleanup_unlink_list(vdev, &vdev->unlink_rx);

With this change, this will be only place unlink_rx is used without
vdev->priv_lock hold? Please explain why this is safe.

quoted

+}
+

Is there a need for this layer?

I added these wrappers purely for convenience. There is no other purpose.
Would you prefer this patch without the wrappers?

Yes. Prefer it without the wrappers. When you take the wrappers
out, I think the unlink_rx could be within spinlock hold easily.

thanks,
-- Shuah
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