linux-kernel - Re: [PATCH] proc: proc_get_inode should de

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Date:	Tue, 24 Feb 2009 10:07:45 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Krzysztof Sachanowicz <analyzer1@...il.com>,
	linux-kernel@...r.kernel.org, marcin.pilipczuk@...il.com,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH] proc: proc_get_inode should de_put when inode already
	initialized

On Mon, Feb 23, 2009 at 03:25:55PM -0800, Andrew Morton wrote:
> On Mon, 23 Feb 2009 22:21:55 +0100
> Krzysztof Sachanowicz <analyzer1@...il.com> wrote:
> 
> > de_get is called before every proc_get_inode, but corresponding de_put is 
> > called only when dropping last reference to an inode. This might cause 
> > something like
> > remove_proc_entry: /proc/stats busy, count=14496
> > to be printed to the syslog.
> > 
> > The fix is to call de_put in case of an already initialized inode in 
> > proc_get_inode.
> > 
> > Signed-off-by: Krzysztof Sachanowicz <analyzer1@...il.com>
> > Tested-by: Marcin Pilipczuk <marcin.pilipczuk@...il.com>
> > ---
> > --- linux-2.6.29-rc6.orig/fs/proc/inode.c	2009-02-23 20:43:32.000000000 +0100
> > +++ linux-2.6.29-rc6/fs/proc/inode.c	2009-02-23 20:46:37.000000000 +0100
> > @@ -485,8 +485,10 @@ struct inode *proc_get_inode(struct supe
> >  			}
> >  		}
> >  		unlock_new_inode(inode);
> > -	} else
> > +	} else {
> >  	       module_put(de->owner);
> > +	       de_put(de);
> > +	}
> >  	return inode;
> >  
> >  out_ino:
> 
> This code area looks quite different in linux-next, although the
> changes there are removing proc_dir_entry.owner altogether and aren't
> obviously targetted at fixing this bug.

->owner issue is independent of this leak, I'll rebase/edit patches as
needed.

> Also...
> 
> It's unpleasing to have the de_get() inside the caller and the de_put()
> inside the callee - it is better to have them both happening at the
> same level.  If it is the case that "de_get is called before every
> proc_get_inode", then perhaps that operation should simply be moved
> into proc_get_inode().

Well, yes, this sucks. But unlock_new_inode() will clear I_NEW state,
so after function returns, there is no way to distinguish.
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