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

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Message-ID: <20150610052023.GA23451@kroah.com>
Date:	Tue, 9 Jun 2015 22:20:23 -0700
From:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:	Lisa Du <cldu@...vell.com>
Cc:	"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 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
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