linux-kernel - Lockdep violation in the serial driver

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Message-ID: <Pine.LNX.4.44L0.0707271726080.2810-100000@iolanthe.rowland.org>
Date:	Fri, 27 Jul 2007 17:33:14 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	linux-serial@...r.kernel.org,
	Kernel development list <linux-kernel@...r.kernel.org>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Lockdep violation in the serial driver

I want to make some changes to the Power Management core, and one of
the side effects will be to make it illegal for a driver to acquire a
mutex within its suspend() or resume() method if that mutex was locked
while the device was registered.

Unfortunately the serial core does exactly that.  In 
drivers/serial/serial_core.c the uart_add_one_port() routine holds 
state->mutex while calling tty_register_device(), and the same mutex is 
acquired by uart_suspend_port() and uart_resume_port().

Can anybody suggest a way around this?  Does the mutex really need to 
be locked at all these times?  Can it be released before calling 
tty_register_device()?  Or could two separate mutexes be used?

Thanks,

Alan Stern

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