On Mon, Feb 17, 2014 at 01:35:56PM -0800, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
>
> (Trivial patch.)
>
> If the code is looking at the RCU-protected pointer itself, but not
> dereferencing it, the rcu_dereference() functions can be downgraded to
> rcu_access_pointer(). This commit makes this downgrade in __alloc_fd(),
> which simply compares the RCU-protected pointer against NULL with no
> dereferencing.
>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
I'm beginning to wonder if this common pattern ought to have an
rcu_pointer_is_null(), which would not return the pointer, only the
boolean.
Regardless, for this patch:
Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> fs/file.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/file.c b/fs/file.c
> index db25c2bdfe46..18f7d27855c4 100644
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -497,7 +497,7 @@ repeat:
> error = fd;
> #if 1
> /* Sanity check */
> - if (rcu_dereference_raw(fdt->fd[fd]) != NULL) {
> + if (rcu_access_pointer(fdt->fd[fd]) != NULL) {
> printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
> rcu_assign_pointer(fdt->fd[fd], NULL);
> }
> --
> 1.8.1.5
>
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