From: Ping Cheng <pinglinux@gmail.com>
To: Jiri Kosina <jikos@kernel.org>
Cc: Ioan-Adrian Ratiu <adi@adirat.com>,
"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
linux-input <linux-input@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
joshc@ni.com, Benjamin Tissoires <benjamin.tissoires@gmail.com>
Subject: Re: [PATCH v2] hid: usbhid: hid-core: fix recursive deadlock
Date: Tue, 1 Dec 2015 16:00:12 -0800 [thread overview]
Message-ID: <CAF8JNh+HEfj7JV-i5yZebwthZn_xFzT7Hra+RWBqFfVtH6_58g@mail.gmail.com> (raw)
In-Reply-To: <alpine.LNX.2.00.1512011736030.32500@pobox.suse.cz>
Hi Jiri,
On Tue, Dec 1, 2015 at 8:36 AM, Jiri Kosina <jikos@kernel.org> wrote:
> On Fri, 20 Nov 2015, Ioan-Adrian Ratiu wrote:
>
>> 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>
>
> Applied to for-4.5/core branch. Thanks,
Since wacom_intuos_schedule_prox_event() was introduced on March 5,
2015, the call was first used in kernel 3.19. Shouldn't we back-port
this patch to other stable versions?
Thank you.
Ping
prev parent reply other threads:[~2015-12-02 0:00 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-18 19:25 [PATCH] hid: usbhid: hid-core: fix recursive deadlock Ioan-Adrian Ratiu
2015-11-18 20:37 ` Jiri Kosina
2015-11-18 21:05 ` Ioan-Adrian Ratiu
2015-11-18 23:58 ` Josh Cartwright
2015-11-19 6:47 ` Ioan-Adrian Ratiu
2015-11-19 9:10 ` Jiri Kosina
2015-11-19 16:33 ` Ioan-Adrian Ratiu
2015-11-19 21:34 ` Jiri Kosina
2015-11-20 20:08 ` Ioan-Adrian Ratiu
2015-11-19 8:56 ` Jiri Kosina
2015-11-20 20:19 ` [PATCH v2] " Ioan-Adrian Ratiu
2015-11-29 10:29 ` Ioan-Adrian Ratiu
2016-01-21 1:28 ` Jason Gerecke
2016-01-21 9:36 ` Jiri Kosina
2015-12-01 16:36 ` Jiri Kosina
2015-12-02 0:00 ` Ping Cheng [this message]
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