The patch titled remove rcu_assign_pointer(NULL) penalty with type/macro safety has been removed from the -mm tree. Its filename was remove-rcu_assign_pointernull-penalty-with-type-macro-safety.patch This patch was dropped because it had testing failures The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: remove rcu_assign_pointer(NULL) penalty with type/macro safety From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> 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 <paulmck@xxxxxxxxxxxxxxxxxx> Cc: Stephen Hemminger <shemminger@xxxxxxxx> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/rcupdate.h | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff -puN include/linux/rcupdate.h~remove-rcu_assign_pointernull-penalty-with-type-macro-safety include/linux/rcupdate.h --- a/include/linux/rcupdate.h~remove-rcu_assign_pointernull-penalty-with-type-macro-safety +++ a/include/linux/rcupdate.h @@ -172,14 +172,19 @@ struct rcu_head { * 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) \ +#define rcu_assign_pointer(p, v) \ ({ \ - if (!__builtin_constant_p(v) || \ - ((v) != NULL)) \ + typeof(*p) *_________p1 = (v); \ + \ + if (!__builtin_constant_p(v) || (_________p1 != NULL)) \ smp_wmb(); \ - (p) = (v); \ + (p) = _________p1; \ }) /** _ Patches currently in -mm which might be from paulmck@xxxxxxxxxxxxxxxxxx are git-sched.patch kthread-add-a-missing-memory-barrier-to-kthread_stop.patch kthread-call-wake_up_process-without-the-lock-being-held.patch remove-rcu_assign_pointernull-penalty-with-type-macro-safety.patch add-rcu_assign_index-if-ever-needed.patch add-rcu_assign_index-if-ever-needed-fix.patch rcu-split-listh-and-move-rcu-protected-lists-into-rculisth.patch lock_task_sighand-add-rcu-lock-unlock.patch k_getrusage-dont-take-rcu_read_lock.patch do_task_stat-dont-take-rcu_read_lock.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html