From: Lisa Du <cldu@marvell.com>
To: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
CC: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: A race condition between debugfs and seq_file operation
Thread-Topic: A race condition between debugfs and seq_file operation
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Date: Wed, 10 Jun 2015 06:18:26 +0000
Message-ID: <cac45ab977954eea86b46f6566b3ee87@SC-EXCH04.marvell.com>
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 <3626bdb18cfc40c98618d0ee68816ab0@SC-EXCH04.marvell.com>
 <20150609211202.GA16801@kroah.com>
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 <20150610052023.GA23451@kroah.com>
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> -----Original Message-----
> From: gregkh@linuxfoundation.org [mailto:gregkh@linuxfoundation.org]
> Sent: 2015年6月10日 13:20
> To: Lisa Du
> Cc: linux-kernel@vger.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@linuxfoundation.org [mailto:gregkh@linuxfoundation.org]
> > > Sent: 2015年6月10日 5:12
> > > To: Lisa Du
> > > Cc: linux-kernel@vger.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,
> > > > client->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.
Ok, I see, thanks!
> 
> thanks,
> 
> greg k-h
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