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

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Message-ID: <20150609211202.GA16801@kroah.com>
Date:	Tue, 9 Jun 2015 14:12:02 -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 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,

greg k-h
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