DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=beta;
        h=received:subject:from:to:content-type:date:message-id:mime-version:x-mailer:content-transfer-encoding;
        b=PcOfNR8IuQyMZ1X/VpTW4YLBkPY1kg8+uEzEJNnyoJT0tfDyfwPCM9QFFuD8s8d6JwCFHBqHNyKLBQuB2KExaF6NqCgk3akfTjTGNnH6eUkKMB2i8TB1iKhj9kYAx+KBn1NkdKzSHJhfHPAhRNrftTbCHGbBjqHxRdT4nKy7ppQ=
Subject: Is this a preempt issue in drivers/input/evdev.c
From: "Yin,Fengwei" <yfw.kernel@gmail.com>
To: linux-kernel@vger.kernel.org
Content-Type: text/plain; charset=UTF-8
Date: Sat, 12 May 2007 11:18:45 +0800
Message-Id: <1178939925.14713.16.camel@localhost.localdomain>
Mime-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1080
Lines: 54

Hi,
When open/close evdev, the code is as following to handle multi-client
operation:
static int evdev_release(...)
{
	...
	if (!--evdev->open) {
		<------------preempted
		if (evdev->exist)
			input_close_device(...);
		else
			evdev_free(evdev);
	}
	return 0;
}

static int evdev_open(...)
{
	...
	if (!evdev->open++ && evdev->exist)｛
		errror = input_open_device(...);
		if (error) {
			...
		}
	}
	...
	return 0;
}

So if the evdev_release() is preempted at the point marked by another
process which will open the evdev, which will make operation sequence
like:

   --evdev->open in evdev_release()
         -----> preempted
	                            evdev->open++ and input_open_devie()
	 <----- reschedule 
	input_close_device()

Should we introduce a mutex here? Or do I miss something? Thanks.

Regards
Yin, Fengwei


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/