linux-kernel - Re: race in sysfs between sysfs_remove

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Message-Id: <200612041735.13615.oliver@neukum.org>
Date:	Mon, 4 Dec 2006 17:35:13 +0100
From:	Oliver Neukum <oliver@...kum.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Maneesh Soni <maneesh@...ibm.com>, gregkh@...e.com,
	linux-usb-devel@...ts.sourceforge.net,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: race in sysfs between sysfs_remove_file() and read()/write() #2

Am Montag, 4. Dezember 2006 17:06 schrieb Alan Stern:
> On Mon, 4 Dec 2006, Maneesh Soni wrote:
> 
> > hmm, I guess Greg has to say the final word. The question is either to fail
> > the IO (-ENODEV) or fail the file removal (-EBUSY). If we are not going to
> > fail the removal then your patch is the way to go.
> > 
> > Greg?
> 
> Oliver is right that we cannot allow device_remove_file() to fail.  In 
> fact we can't even allow it to block until all the existing open file 
> references are closed.

Yes, we must have an upper bound with respect to time.

> Our major questions have to do with the details of the patch itself.  In 
> particular, we are worried about possible races with the VFS and the 
> handling of the inode's usage count.  Can you examine the patch carefully 
> to see if it is okay?
> 
> Also, Oliver, it looks like the latest version of your patch makes an 
> unnecessary change to sysfs_remove_file().

Code like:

int d(int a, int b)
{
	return a + b;
}

int c(int a, int b)
{
	return d(a, b);
}

is a detrimental to correct understanding and thence coding.
In fact reading sysfs source code is like jumping all around the kernel
tree. Such changes made it readable by normal people. I have to
understand which method I am coding on to do reasonable work. ;-)

	Regards
		Oliver
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