netpoll: more efficient locking
Callers of netpoll_poll_lock() own NAPI_STATE_SCHED
Callers of netpoll_poll_unlock() have BH blocked between
the NAPI_STATE_SCHED being cleared and poll_lock is released.
We can avoid the spinlock which has no contention, and use cmpxchg()
on poll_owner which we need to set anyway.
This removes a possible lockdep violation after the cited commit,
since sk_busy_loop() re-enables BH before calling busy_poll_stop()
Fixes: 217f69743681 ("net: busy-poll: allow preemption in sk_busy_loop()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index b25ee9f..1828900 100644
--- a/include/linux/netpoll.h
+++ b/include/linux/netpoll.h
@@ -78,8 +78,11 @@ static inline void *netpoll_poll_lock(struct napi_struct *napi)
struct net_device *dev = napi->dev;
if (dev && dev->npinfo) {
- spin_lock(&napi->poll_lock);
- napi->poll_owner = smp_processor_id();
+ int owner = smp_processor_id();
+
+ while (cmpxchg(&napi->poll_owner, -1, owner) != -1)
+ cpu_relax();
+
return napi;
}
return NULL;
@@ -89,10 +92,8 @@ static inline void netpoll_poll_unlock(void *have)
{
struct napi_struct *napi = have;
- if (napi) {
- napi->poll_owner = -1;
- spin_unlock(&napi->poll_lock);
- }
+ if (napi)
+ smp_store_release(&napi->poll_owner, -1);
}
static inline bool netpoll_tx_running(struct net_device *dev)