Re: [PATCH tip/core/rcu 07/13] vfs: apply lockdep-based checking to rcu_dereference() uses

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Sun, Feb 14, 2010 at 11:12:10AM +0100, Peter Zijlstra wrote:
> On Thu, 2010-02-11 at 16:00 -0800, Paul E. McKenney wrote:
> > 
> > -#define files_fdtable(files) (rcu_dereference((files)->fdt))
> > +#define files_fdtable(files) \
> > +       (rcu_dereference_check((files)->fdt, \
> > +                              rcu_read_lock_held() || \
> > +                              lockdep_is_held(&(files)->file_lock) ||
> > \
> > +                              atomic_read(&files->count) == 1))
> >  
> >  struct file_operations;
> >  struct vfsmount;
> > @@ -78,7 +82,7 @@ static inline struct file * fcheck_files(struct files_struct *files, unsigned in
> >         struct fdtable *fdt = files_fdtable(files);
> >  
> >         if (fd < fdt->max_fds)
> > -               file = rcu_dereference(fdt->fd[fd]);
> > +               file = rcu_dereference_check(fdt->fd[fd], rcu_read_lock_held() || lockdep_is_held(&files->file_lock) || atomic_read(&files->count) == 1);
> >         return file; 
> 
> I'm almost thinking you can do something smart here and not replicate
> that condition :-)

;-)

How about like the following?  If this is agreeable, I will re-send the
patch stack with this included.

							Thanx, Paul

------------------------------------------------------------------------

vfs: abstract rcu_dereference_check for files-fdtable use

Create an rcu_dereference_check_fdtable() that encapsulates the
rcu_dereference_check() condition for fcheck_files() use.  This has
the beneficial side-effect of getting rid of a very long line.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---

diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index 144412f..013dc52 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -57,11 +57,14 @@ struct files_struct {
 	struct file * fd_array[NR_OPEN_DEFAULT];
 };
 
-#define files_fdtable(files) \
-	(rcu_dereference_check((files)->fdt, \
+#define rcu_dereference_check_fdtable(files, fdtfd) \
+	(rcu_dereference_check((fdtfd), \
 			       rcu_read_lock_held() || \
 			       lockdep_is_held(&(files)->file_lock) || \
-			       atomic_read(&files->count) == 1))
+			       atomic_read(&(files)->count) == 1))
+
+#define files_fdtable(files) \
+		(rcu_dereference_check_fdtable((files), (files)->fdt))
 
 struct file_operations;
 struct vfsmount;
@@ -82,7 +85,7 @@ static inline struct file * fcheck_files(struct files_struct *files, unsigned in
 	struct fdtable *fdt = files_fdtable(files);
 
 	if (fd < fdt->max_fds)
-		file = rcu_dereference_check(fdt->fd[fd], rcu_read_lock_held() || lockdep_is_held(&files->file_lock) || atomic_read(&files->count) == 1);
+		file = rcu_dereference_check_fdtable(files, fdt->fd[fd]);
 	return file;
 }