linux-kernel - Re: A race condition between debugfs and seq

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Date:	Wed, 10 Jun 2015 07:49:28 -0700
From:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:	Matthias Schiffer <mschiffer@...verse-factory.net>
Cc:	Lisa Du <cldu@...vell.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: A race condition between debugfs and seq_file operation

On Wed, Jun 10, 2015 at 04:00:37PM +0200, Matthias Schiffer wrote:
> On 06/10/2015 07:20 AM, gregkh@...uxfoundation.org wrote:
> > On Wed, Jun 10, 2015 at 05:00:03AM +0000, Lisa Du wrote:
> >>> -----Original Message-----
> >>> From: gregkh@...uxfoundation.org [mailto:gregkh@...uxfoundation.org]
> >>> Sent: 2015年6月10日 5:12
> >>> To: Lisa Du
> >>> Cc: linux-kernel@...r.kernel.org
> >>> Subject: Re: A race condition between debugfs and seq_file operation
> >>>
> >>> On Mon, Jun 08, 2015 at 04:28:10AM +0000, Lisa Du wrote:
> >>>> Hi, All
> >>>> Recently I met one race condition related to debugfs.
> >>>>
> >>>> Take an example from ion.c in kernel3.14:
> >>>> static int ion_debug_client_open(struct inode *inode, struct file
> >>>> *file) {
> >>>> 	return single_open(file, ion_debug_client_show, inode->i_private); }
> >>>>
> >>>> static const struct file_operations debug_client_fops = {
> >>>> 	.open = ion_debug_client_open,
> >>>> 	.read = seq_read,
> >>>> 	.llseek = seq_lseek,
> >>>> 	.release = single_release,
> >>>> };
> >>>> client->debug_root = debugfs_create_file(client->display_name, 0664,
> >>>> 					dev->clients_debug_root,
> >>>> 					client, &debug_client_fops);
> >>>>
> >>>> I find during I read the debugfs node, driver can do
> >>>> debugfs_remove_recursive(dentry); Is it expected?
> >>>
> >>> Yes.  Well, not "expected", but a mess, yes.
> >>>
> >>> Removing debugfs files are known to have lots of races, this isn't the only
> >>> one :(
> >> Thanks for the reply! 
> >> Not sure if there is any plan to resolve such races in the future?
> > 
> > Yes, I have "plans", but it's on my very long todo list behind lots of
> > other things...
> > 
> > If you want to look into it, please, that would be wonderful.
> > 
> > thanks,
> > 
> > greg k-h
> 
> I've stumbled across related issues a few days ago (mostly in network
> drivers). What I've found out:

<snip>

Yes, all of these are issues, as I mentioned.

greg k-h
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