linux-kernel - Re: [PATCH 1/1] vfs: umount

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Date:	Fri, 24 Apr 2009 08:15:36 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Alessio Igor Bogani <abogani@...ware.it>
Cc:	Jonathan Corbet <corbet@....net>,
	Fr??d??ric Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	LFSDEV <linux-fsdevel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, Matthew Wilcox <matthew@....cx>
Subject: Re: [PATCH 1/1] vfs: umount_begin BKL pushdown v2

On Fri, Apr 24, 2009 at 08:13:12AM +0100, Al Viro wrote:
> On Fri, Apr 24, 2009 at 09:06:53AM +0200, Alessio Igor Bogani wrote:
> >  static void cifs_umount_begin(struct super_block *sb)
> >  {
> > -	struct cifs_sb_info *cifs_sb = CIFS_SB(sb);
> > +	struct cifs_sb_info *cifs_sb;
> >  	struct cifsTconInfo *tcon;
> >  
> > -	if (cifs_sb == NULL)
> > +	lock_kernel();
> > +	cifs_sb = CIFS_SB(sb);
> > +
> > +	if (cifs_sb == NULL) {
> > +		unlock_kernel();
> >  		return;
> > +	}
> >  
> >  	tcon = cifs_sb->tcon;
> > -	if (tcon == NULL)
> > +	if (tcon == NULL) {
> > +		unlock_kernel();
> >  		return;
> > +	}
> 
> AFAICS, both CIFS_SB(sb) and ->tcon are assign-once, so lock_kernel() should
> really go here (if it can't be removed completely, of course, but that's up
> to CIFS folks).  Applied with such modification.

PS: I suspect that checks for NULL are actually "what if kernel memory got
corrupted", but I'm too lazy to verify that at the moment; again, up to
CIFS folks.
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