Patch "HID: usbhid: fix recursive deadlock" has been added to the 4.3-stable tree

Patch "HID: usbhid: fix recursive deadlock" has been added to the 4.3-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    HID: usbhid: fix recursive deadlock

to the 4.3-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     hid-usbhid-fix-recursive-deadlock.patch
and it can be found in the queue-4.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From e470127e9606b1fa151c4184243e61296d1e0c0f Mon Sep 17 00:00:00 2001
From: Ioan-Adrian Ratiu <adi@adirat.com>
Date: Fri, 20 Nov 2015 22:19:02 +0200
Subject: HID: usbhid: fix recursive deadlock

From: Ioan-Adrian Ratiu <adi@adirat.com>

commit e470127e9606b1fa151c4184243e61296d1e0c0f upstream.

The critical section protected by usbhid->lock in hid_ctrl() is too
big and because of this it causes a recursive deadlock. "Too big" means
the case statement and the call to hid_input_report() do not need to be
protected by the spinlock (no URB operations are done inside them).

The deadlock happens because in certain rare cases drivers try to grab
the lock while handling the ctrl irq which grabs the lock before them
as described above. For example newer wacom tablets like 056a:033c try
to reschedule proximity reads from wacom_intuos_schedule_prox_event()
calling hid_hw_request() -> usbhid_request() -> usbhid_submit_report()
which tries to grab the usbhid lock already held by hid_ctrl().

There are two ways to get out of this deadlock:
    1. Make the drivers work "around" the ctrl critical region, in the
    wacom case for ex. by delaying the scheduling of the proximity read
    request itself to a workqueue.
    2. Shrink the critical region so the usbhid lock protects only the
    instructions which modify usbhid state, calling hid_input_report()
    with the spinlock unlocked, allowing the device driver to grab the
    lock first, finish and then grab the lock afterwards in hid_ctrl().

This patch implements the 2nd solution.

Signed-off-by: Ioan-Adrian Ratiu <adi@adirat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/hid/usbhid/hid-core.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/hid/usbhid/hid-core.c
+++ b/drivers/hid/usbhid/hid-core.c
@@ -477,8 +477,6 @@ static void hid_ctrl(struct urb *urb)
 	struct usbhid_device *usbhid = hid->driver_data;
 	int unplug = 0, status = urb->status;
 
-	spin_lock(&usbhid->lock);
-
 	switch (status) {
 	case 0:			/* success */
 		if (usbhid->ctrl[usbhid->ctrltail].dir == USB_DIR_IN)
@@ -498,6 +496,8 @@ static void hid_ctrl(struct urb *urb)
 		hid_warn(urb->dev, "ctrl urb status %d received\n", status);
 	}
 
+	spin_lock(&usbhid->lock);
+
 	if (unplug) {
 		usbhid->ctrltail = usbhid->ctrlhead;
 	} else {


Patches currently in stable-queue which might be from adi@adirat.com are

queue-4.3/hid-usbhid-fix-recursive-deadlock.patch