linux-kernel - Re: [linux-pm] wacom + runtime PM = AA deadlock

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Date:	Mon, 13 Sep 2010 10:25:38 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Jiri Slaby <jslaby@...e.cz>
cc:	Oliver Neukum <oliver@...kum.org>, <pingc@...om.com>,
	Dmitry Torokhov <dtor@...l.ru>,
	linux-pm <linux-pm@...ts.linux-foundation.org>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	<linux-input@...r.kernel.org>
Subject: Re: [linux-pm] wacom + runtime PM = AA deadlock

On Mon, 13 Sep 2010, Jiri Slaby wrote:

> Hi,
> 
> by mistake when runtime PM is enabled by default for input devices, X
> hangs on wacom open:
> [<ffffffff814a00ea>] mutex_lock+0x1a/0x40
> [<ffffffffa02bc94b>] wacom_resume+0x3b/0x90 [wacom]
> [<ffffffff81327a32>] usb_resume_interface+0xd2/0x190
> [<ffffffff81327b5d>] usb_resume_both+0x6d/0x110
> [<ffffffff81327c24>] usb_runtime_resume+0x24/0x40
> [<ffffffff8130a2cf>] __pm_runtime_resume+0x26f/0x450
> [<ffffffff8130a23a>] __pm_runtime_resume+0x1da/0x450
> [<ffffffff8130a53a>] pm_runtime_resume+0x2a/0x50
> [<ffffffff81328176>] usb_autopm_get_interface+0x26/0x60
> [<ffffffffa02bc626>] wacom_open+0x36/0x90 [wacom]
> 
> wacom_open took wacom->lock and calls usb_autopm_get_interface which in
> turn calls wacom_resume which tries to aquire the lock again.
> 
> More details (dmesg including) at:
> https://bugzilla.novell.com/show_bug.cgi?id=638506
> 
> Any ideas how to fix that properly?

One possibility is for wacom_open simply not to acquire the lock until
after the usb_autopm_get_interface call returns.  And why does
wacom_open have that assignment to wacom->irq->dev?  The value was
already set in wacom_probe.

BTW, does anybody know why wacom_open calls usb_autopm_get_interface 
but wacom_close doesn't call usb_autopm_put_interface?

Alan Stern

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