linux-kernel - Is this a preempt issue in drivers/input/evdev.c

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Message-Id: <1178939925.14713.16.camel@localhost.localdomain>
Date:	Sat, 12 May 2007 11:18:45 +0800
From:	"Yin,Fengwei" <yfw.kernel@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Is this a preempt issue in drivers/input/evdev.c

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


	



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