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


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