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authorEric Dumazet <edumazet@google.com>2016-11-16 14:54:50 -0800
committerDavid S. Miller <davem@davemloft.net>2016-11-16 18:32:02 -0500
commit89c4b442b78bdba388337cc746fe63caba85f46c (patch)
tree825a8d6e04cdc937950e9d8a79b52eeb249236c3
parent1629dd4f763cc15ac3b2711ac65dab153b738c6d (diff)
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>
-rw-r--r--include/linux/netdevice.h1
-rw-r--r--include/linux/netpoll.h13
-rw-r--r--net/core/dev.c1
-rw-r--r--net/core/netpoll.c6
4 files changed, 10 insertions, 11 deletions
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index bcddf951ccee..e84800edd249 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -316,7 +316,6 @@ struct napi_struct {
unsigned int gro_count;
int (*poll)(struct napi_struct *, int);
#ifdef CONFIG_NETPOLL
- spinlock_t poll_lock;
int poll_owner;
#endif
struct net_device *dev;
diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index b25ee9ffdbe6..1828900c9411 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)
diff --git a/net/core/dev.c b/net/core/dev.c
index edba9efeb2e9..f71b34ab57a5 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5143,7 +5143,6 @@ void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
list_add(&napi->dev_list, &dev->napi_list);
napi->dev = dev;
#ifdef CONFIG_NETPOLL
- spin_lock_init(&napi->poll_lock);
napi->poll_owner = -1;
#endif
set_bit(NAPI_STATE_SCHED, &napi->state);
diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 53599bd0c82d..9424673009c1 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -171,12 +171,12 @@ static void poll_one_napi(struct napi_struct *napi)
static void poll_napi(struct net_device *dev)
{
struct napi_struct *napi;
+ int cpu = smp_processor_id();
list_for_each_entry(napi, &dev->napi_list, dev_list) {
- if (napi->poll_owner != smp_processor_id() &&
- spin_trylock(&napi->poll_lock)) {
+ if (cmpxchg(&napi->poll_owner, -1, cpu) == -1) {
poll_one_napi(napi);
- spin_unlock(&napi->poll_lock);
+ smp_store_release(&napi->poll_owner, -1);
}
}
}