On Mon, Feb 17, 2014 at 04:04:31PM -0800, Josh Triplett wrote: > On Mon, Feb 17, 2014 at 03:05:11PM -0800, Paul E. McKenney wrote: > > On Mon, Feb 17, 2014 at 02:00:15PM -0800, Josh Triplett wrote: > > > 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. > > > > Or perhaps an rcu_compare_pointer() to also handle the various cases like: > > > > if (rcu_dereference_raw(foop) == barp) ... > > > > I added the problem to the RCU cleanup list on the OPW site, and > > your solution or my elaboration of it might be the right thing to do. > > (Inspected all 1300 uses of members of the rcu_dereference() family of > > functions last week, and was feeling a bit buggy-eyed at the end...) > > rcu_pointer_eq and/or rcu_pointer_neq might make sense, yeah, as > self-documenting versions of the most sensible way to do the operation, > to steer people away from rcu_dereference or rcu_dereference_raw. Good point! I added this to http://kernelnewbies.org/OPWIntro-RCU?action=show, crediting you for the idea. Thanx, Paul > - Jsoh Triplett > > > Thanx, Paul > > > > > 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 > > > > > > > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
