On Wed, 25 Apr 2012, Oliver Neukum wrote:
> From 9ff6b78dc59c98b9844dc9922549fd338828a889 Mon Sep 17 00:00:00 2001
> From: Oliver Neukum <oliver@xxxxxxxxxx>
> Date: Wed, 25 Apr 2012 12:50:37 +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.
Simply preventing resubmission is a good idea.
> Signed-off-by: Oliver Neukum <oneukum@xxxxxxx>
> ---
> drivers/hid/usbhid/hid-core.c | 61 +++++++++++++++++++++++++++++++++++++----
> drivers/usb/core/urb.c | 30 ++++++++++++++++++++
> include/linux/usb.h | 2 +
> 3 files changed, 87 insertions(+), 6 deletions(-)
This should be split into two patches: one for usbhid and one for
usbcore.
> +void usb_block_urb(struct urb *urb)
> +{
> + if (!urb)
> + return;
> +
> + atomic_inc(&urb->reject);
> +}
> +EXPORT_SYMBOL_GPL(usb_block_urb);
Personally, I prefer
if (urb)
atomic_inc(&urb->reject);
It's a matter of taste; do what you want.
> +void usb_unblock_urb(struct urb *urb)
> +{
> + if (!urb)
> + return;
> +
> + atomic_dec(&urb->reject);
> +}
> +EXPORT_SYMBOL_GPL(usb_unblock_urb);
As was pointed out, this could be eliminated by...
> +
> +/**
> * 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);
changing this to
#define usb_unblock_urb usb_unpoison_urb
Alan Stern
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