Re: [PATCH] hid: usbhid: fix possible deadlock in __usbhid_submit_report

[Ming Lei <ming.lei@canonical.com>]

On Wed, Apr 25, 2012 at 4:06 PM, Oliver Neukum <oneukum@suse.de> wrote:

>
> Indeed. Upon further thought it seems to me that we need to prevent
> resubmission and all is well. And we almost have all the infrastructure.
>
> So how about this, making it more reusable:

Yes, this one is good, better than the adding lock.

>
> From ce77d793252d1abf3a0ec6c67e4a7a05ac6d846a Mon Sep 17 00:00:00 2001
> From: Oliver Neukum <oliver@neukum.org>
> Date: Wed, 25 Apr 2012 09:54:00 +0200
> Subject: [PATCH] usbhid: prevent deadlock during timeout
>
> On some HCDs usb_unlink_urb() can directly call the
> completion handler. That limits the spinlocks that can
> be taken in the handler to locks not held while calling
> usb_unlink_urb()
> To prevent a race with resubmission, this patch exposes
> usbcore's infrastructure for blocking submission, uses it
> and so drops the lock without causing a race in usbhid.
>
> Signed-off-by: Oliver Neukum <oneukum@suse.de>
> ---
>  drivers/hid/usbhid/hid-core.c |   38 ++++++++++++++++++++++++++++++++++----
>  drivers/usb/core/urb.c        |   30 ++++++++++++++++++++++++++++++
>  include/linux/usb.h           |    2 ++
>  3 files changed, 66 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/hid/usbhid/hid-core.c b/drivers/hid/usbhid/hid-core.c
> index 5bf91db..763257d 100644
> --- a/drivers/hid/usbhid/hid-core.c
> +++ b/drivers/hid/usbhid/hid-core.c
> @@ -535,11 +535,27 @@ static void __usbhid_submit_report(struct hid_device *hid, struct hid_report *re
>                         * the queue is known to run
>                         * but an earlier request may be stuck
>                         * we may need to time out
> -                        * no race because this is called under
> +                        * no race because the URB is blocked under
>                         * spinlock
>                         */
> -                       if (time_after(jiffies, usbhid->last_out + HZ * 5))
> +                       if (time_after(jiffies, usbhid->last_out + HZ * 5)) {
> +                               usb_block_urb(usbhid->urbout);
> +                               /* drop lock to not deadlock if the callback is called */
> +                               spin_unlock(&usbhid->lock);
>                                usb_unlink_urb(usbhid->urbout);
> +                               spin_lock(&usbhid->lock);
> +                               usb_unblock_urb(usbhid->urbout);
> +                               /*
> +                                * if the unlinking has already completed
> +                                * the pump will have been stopped
> +                                * it must be restarted now
> +                                */
> +                               if (!test_bit(HID_OUT_RUNNING, &usbhid->iofl))
> +                                       if (!hid_submit_out(hid))

You need to add check of "usbhid->outtail != usbhid->outhead" above.

> +                                               set_bit(HID_OUT_RUNNING, &usbhid->iofl);
> +
> +
> +                       }
>                }
>                return;
>        }
> @@ -583,11 +599,25 @@ static void __usbhid_submit_report(struct hid_device *hid, struct hid_report *re
>                 * the queue is known to run
>                 * but an earlier request may be stuck
>                 * we may need to time out
> -                * no race because this is called under
> +                * no race because the URB is blocked under
>                 * spinlock
>                 */
> -               if (time_after(jiffies, usbhid->last_ctrl + HZ * 5))
> +               if (time_after(jiffies, usbhid->last_ctrl + HZ * 5)) {
> +                       usb_block_urb(usbhid->urbctrl);
> +                       /* drop lock to not deadlock if the callback is called */
> +                       spin_unlock(&usbhid->lock);
>                        usb_unlink_urb(usbhid->urbctrl);
> +                       spin_lock(&usbhid->lock);
> +                       usb_unblock_urb(usbhid->urbctrl);
> +                       /*
> +                        * if the unlinking has already completed
> +                        * the pump will have been stopped
> +                        * it must be restarted now
> +                        */
> +                       if (!test_bit(HID_CTRL_RUNNING, &usbhid->iofl))
> +                               if (!hid_submit_ctrl(hid))

Similar as above.

> +                                       set_bit(HID_CTRL_RUNNING, &usbhid->iofl);
> +               }
>        }
>  }
>
> diff --git a/drivers/usb/core/urb.c b/drivers/usb/core/urb.c
> index cd9b3a2..1d1b010 100644
> --- a/drivers/usb/core/urb.c
> +++ b/drivers/usb/core/urb.c
> @@ -681,6 +681,36 @@ void usb_unpoison_urb(struct urb *urb)
>  EXPORT_SYMBOL_GPL(usb_unpoison_urb);
>
>  /**
> + * usb_block_urb - reliably prevent further use of an URB
> + * @urb: pointer to URB to be blocked, may be NULL
> + *
> + * After the routine has run, attempts to resubmit the URB will fail
> + * with error -EPERM.  Thus even if the URB's completion handler always
> + * tries to resubmit, it will not succeed and the URB will become idle.
> + *
> + * The URB must not be deallocated while this routine is running.  In
> + * particular, when a driver calls this routine, it must insure that the
> + * completion handler cannot deallocate the URB.
> + */
> +void usb_block_urb(struct urb *urb)
> +{
> +        if (!urb)
> +                return;
> +
> +        atomic_inc(&urb->reject);
> +}
> +EXPORT_SYMBOL_GPL(usb_block_urb);
> +
> +void usb_unblock_urb(struct urb *urb)
> +{
> +        if (!urb)
> +                return;
> +
> +        atomic_dec(&urb->reject);
> +}
> +EXPORT_SYMBOL_GPL(usb_unblock_urb);
> +
> +/**
>  * usb_kill_anchored_urbs - cancel transfer requests en masse
>  * @anchor: anchor the requests are bound to
>  *
> diff --git a/include/linux/usb.h b/include/linux/usb.h
> index 73b68d1..23df8ae 100644
> --- a/include/linux/usb.h
> +++ b/include/linux/usb.h
> @@ -1379,6 +1379,8 @@ extern int usb_unlink_urb(struct urb *urb);
>  extern void usb_kill_urb(struct urb *urb);
>  extern void usb_poison_urb(struct urb *urb);
>  extern void usb_unpoison_urb(struct urb *urb);
> +extern void usb_block_urb(struct urb *urb);
> +extern void usb_unblock_urb(struct urb *urb);
>  extern void usb_kill_anchored_urbs(struct usb_anchor *anchor);
>  extern void usb_poison_anchored_urbs(struct usb_anchor *anchor);
>  extern void usb_unpoison_anchored_urbs(struct usb_anchor *anchor);


Thanks,
--
Ming Lei
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