[PATCH net-next] net: relax rtnl_dereference()
From: Eric Dumazet <hidden>
Date: 2010-10-04 09:00:17
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
Le lundi 04 octobre 2010 à 10:42 +0200, Eric Dumazet a écrit :
BTW, rtnl_dereference() should be changed to use rcu_dereference_protected() instead of rcu_dereference_check() : If RTBL is held, there is no need to force a barrier.
[PATCH net-next] net: relax rtnl_dereference() rtnl_dereference() is used in contexts where RTNL is held, to fetch an RCU protected pointer. Updates to this pointer are prevented by RTNL, so we dont need smp_read_barrier_depends() and the ACCESS_ONCE() provided in rcu_dereference_check(). rtnl_dereference() is mainly a macro to document the locking invariant. Signed-off-by: Eric Dumazet <redacted> --- include/linux/rtnetlink.h | 10 ++++++---- 1 files changed, 6 insertions(+), 4 deletions(-)
diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index 68c436b..d3c4efa 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h@@ -754,20 +754,22 @@ extern int lockdep_rtnl_is_held(void); * @p: The pointer to read, prior to dereferencing * * Do an rcu_dereference(p), but check caller either holds rcu_read_lock() - * or RTNL + * or RTNL. Note : Please prefer rtnl_dereference() or rcu_dereference() */ #define rcu_dereference_rtnl(p) \ rcu_dereference_check(p, rcu_read_lock_held() || \ lockdep_rtnl_is_held()) /** - * rtnl_dereference - rcu_dereference with debug checking + * rtnl_dereference - fetch RCU pointer when updates are prevented by RTNL * @p: The pointer to read, prior to dereferencing * - * Do an rcu_dereference(p), but check caller holds RTNL + * Return the value of the specified RCU-protected pointer, but omit + * both the smp_read_barrier_depends() and the ACCESS_ONCE(), because + * caller holds RTNL. */ #define rtnl_dereference(p) \ - rcu_dereference_check(p, lockdep_rtnl_is_held()) + rcu_dereference_protected(p, lockdep_rtnl_is_held()) extern void rtnetlink_init(void); extern void __rtnl_unlock(void);