linux-kernel - Re: + procfs-directory-entry-cleanup.patch added to -mm tree

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Message-ID: <20070522201638.GB5689@martell.zuzino.mipt.ru>
Date:	Wed, 23 May 2007 00:16:39 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, xiaosuo@...il.com
Subject: Re: + procfs-directory-entry-cleanup.patch added to -mm tree

On Tue, May 22, 2007 at 11:29:51AM -0700, Andrew Morton wrote:
> On Tue, 22 May 2007 21:43:49 +0400
> Alexey Dobriyan <adobriyan@...il.com> wrote:
> 
> > On Sun, May 20, 2007 at 08:41:02PM -0700, akpm@...ux-foundation.org wrote:
> > > Subject: procfs directory entry cleanup
> > > From: "Changli Gao" <xiaosuo@...il.com>
> > >
> > > Function proc_register() will assign proc_dir_operations and
> > > proc_dir_inode_operations to ent's members proc_fops and proc_iops
> > > correctly if ent is a directory. So the early assignment isn't
> > > necessary.
> > 
> > > --- a/fs/proc/generic.c~procfs-directory-entry-cleanup
> > > +++ a/fs/proc/generic.c
> > > @@ -649,9 +649,6 @@ struct proc_dir_entry *proc_mkdir_mode(c
> > >  
> > >  	ent = proc_create(&parent, name, S_IFDIR | mode, 2);
> > >  	if (ent) {
> > > -		ent->proc_fops = &proc_dir_operations;
> > > -		ent->proc_iops = &proc_dir_inode_operations;
> > > -
> > >  		if (proc_register(parent, ent) < 0) {
> > >  			kfree(ent);
> > >  			ent = NULL;
> > > @@ -686,10 +683,6 @@ struct proc_dir_entry *create_proc_entry
> > >  
> > >  	ent = proc_create(&parent,name,mode,nlink);
> > >  	if (ent) {
> > > -		if (S_ISDIR(mode)) {
> > > -			ent->proc_fops = &proc_dir_operations;
> > > -			ent->proc_iops = &proc_dir_inode_operations;
> > > -		}
> > >  		if (proc_register(parent, ent) < 0) {
> > >  			kfree(ent);
> > >  			ent = NULL;
> > 
> > This should add race because new PDE for directory will be glued to tree
> > with NULL ->proc_iops and, at least, vfs_getattr() doesn't check for
> > NULL ->i_op.
> > 
> > I've tried to reproduce this scenario with udelay() inserted before
> > S_ISDIR checks in proc_register() but got some panic while in X,
> > so no cookie for me. Maybe it's impossible, indeed.
> > 
> > Anyway, this patch + moving ->proc_fops and ->proc_iops initialization
> > before gluing is OK with me.
> 
> Like this?

Yes, exactly.

> --- a/fs/proc/generic.c~procfs-directory-entry-cleanup-fix
> +++ a/fs/proc/generic.c
> @@ -529,12 +529,6 @@ static int proc_register(struct proc_dir
>  		return -EAGAIN;
>  	dp->low_ino = i;
>  
> -	spin_lock(&proc_subdir_lock);
> -	dp->next = dir->subdir;
> -	dp->parent = dir;
> -	dir->subdir = dp;
> -	spin_unlock(&proc_subdir_lock);
> -
>  	if (S_ISDIR(dp->mode)) {
>  		if (dp->proc_iops == NULL) {
>  			dp->proc_fops = &proc_dir_operations;
> @@ -550,6 +544,13 @@ static int proc_register(struct proc_dir
>  		if (dp->proc_iops == NULL)
>  			dp->proc_iops = &proc_file_inode_operations;
>  	}
> +
> +	spin_lock(&proc_subdir_lock);
> +	dp->next = dir->subdir;
> +	dp->parent = dir;
> +	dir->subdir = dp;
> +	spin_unlock(&proc_subdir_lock);
> +
>  	return 0;
>  }
>  
> _

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