linux-kernel - Re: [PATCH] hid: usbhid: hid-core: fix recursive deadlock

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Message-ID: <alpine.LNX.2.00.1511191005240.20111@pobox.suse.cz>
Date:	Thu, 19 Nov 2015 10:10:19 +0100 (CET)
From:	Jiri Kosina <jikos@...nel.org>
To:	Ioan-Adrian Ratiu <adi@...rat.com>
cc:	Josh Cartwright <joshc@...com>, pinglinux@...il.com,
	linux-usb@...r.kernel.org, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hid: usbhid: hid-core: fix recursive deadlock

On Thu, 19 Nov 2015, Ioan-Adrian Ratiu wrote:

> First part of lockdep report:
> http://imgur.com/clLsCWe
> 
> Second part:
> http://imgur.com/Wa2PzRl
> 
> Here are some printk's of mine while reproducing + debugging the issue:
> http://imgur.com/SETOHT7

So the real problem is that Intuos driver is calling hid_hw_request() 
(which tries to grab the lock in usbhid_submit_report()) while handling 
the CTRL IRQ (lock gets acquired there).

So the proper way to fix seems to be delaying the scheduling of the 
proximity read event in wacom_intuos_inout() to workqueue.

> I'll continue to research this more in depth, but progress is slow 
> because I don't have much time, I'm doing this in my spare time because 
> it's my girlfriend's tablet.

Oh, now I understand the level of severity of this bug! :-)

Thanks,

-- 
Jiri Kosina
SUSE Labs

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