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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 <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David S. Miller 2010-10-05 00:29:48 -07:00
parent 13f5bf18ba
commit 29fa060eab
1 changed files with 6 additions and 4 deletions
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10
include/linux/rtnetlink.h
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@ -755,20 +755,22 @@ extern int lockdep_rtnl_is_held(void);
* @p: The pointer to read, prior to dereferencing * @p: The pointer to read, prior to dereferencing
* *
* Do an rcu_dereference(p), but check caller either holds rcu_read_lock() * 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) \ #define rcu_dereference_rtnl(p) \
rcu_dereference_check(p, rcu_read_lock_held() || \ rcu_dereference_check(p, rcu_read_lock_held() || \
lockdep_rtnl_is_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 * @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) \ #define rtnl_dereference(p) \
rcu_dereference_check(p, lockdep_rtnl_is_held()) rcu_dereference_protected(p, lockdep_rtnl_is_held())
static inline struct netdev_queue *dev_ingress_queue(struct net_device *dev) static inline struct netdev_queue *dev_ingress_queue(struct net_device *dev)
{ {