On Wed, 13 Feb 2008 14:00:24 -0800 "Paul E. McKenney" <[EMAIL PROTECTED]> wrote:
> Hello! > > This is an updated version of the patch posted last November: > > http://archives.free.net.ph/message/20071201.003721.cd6ff17c.en.html > > This new version permits arguments with side effects, for example: > > rcu_assign_pointer(global_p, p++); > > and also verifies that the arguments are pointers, while still avoiding > the unnecessary memory barrier when assigning NULL to a pointer. > This memory-barrier avoidance means that rcu_assign_pointer() is now only > permitted for pointers (not array indexes), and so this version emits a > compiler warning if the first argument is not a pointer. I built a "make > allyesconfig" version on an x86 system, and received no such warnings. > If RCU is ever applied to array indexes, then the second patch in this > series should be applied, and the resulting rcu_assign_index() be used. > > Given the rather surprising history of subtlely broken implementations of > rcu_assign_pointer(), I took the precaution of generating a full set of > test cases and verified that memory barriers and compiler warnings were > emitted when required. I guess it is the simple things that get you... > > Signed-off-by: Paul E. McKenney <[EMAIL PROTECTED]> > --- > > rcupdate.h | 16 ++++++++++++---- > 1 file changed, 12 insertions(+), 4 deletions(-) > > diff -urpNa -X dontdiff linux-2.6.24/include/linux/rcupdate.h > linux-2.6.24-rap/include/linux/rcupdate.h > --- linux-2.6.24/include/linux/rcupdate.h 2008-01-24 14:58:37.000000000 > -0800 > +++ linux-2.6.24-rap/include/linux/rcupdate.h 2008-02-13 13:36:47.000000000 > -0800 whoop, ancient kernel alert. > @@ -270,12 +270,20 @@ extern struct lockdep_map rcu_lock_map; > * structure after the pointer assignment. More importantly, this > * call documents which pointers will be dereferenced by RCU read-side > * code. > + * > + * Throws a compiler warning for non-pointer arguments. > + * > + * Does not insert a memory barrier for a NULL pointer. > */ > > -#define rcu_assign_pointer(p, v) ({ \ > - smp_wmb(); \ > - (p) = (v); \ > - }) > +#define rcu_assign_pointer(p, v) \ > + ({ \ > + typeof(*p) *_________p1 = (v); \ > + \ > + if (!__builtin_constant_p(v) || (_________p1 != NULL)) \ > + smp_wmb(); \ > + (p) = _________p1; \ > + }) Someone already merged the dont-do-it-for-NULL patch so I reworked this appropriately. Was too lazy to update the changelog though. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
