net: make napi_disable() symmetric with enable

Commit 3765996e4f0b ("napi: fix race inside napi_enable") fixed
an ordering bug in napi_enable() and made the napi_enable() diverge
from napi_disable(). The state transitions done on disable are
not symmetric to enable.

There is no known bug in napi_disable() this is just refactoring.

Eric suggests we can also replace msleep(1) with a more opportunistic
usleep_range().

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index 62ddd7d..fa989ab 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6900,19 +6900,25 @@ EXPORT_SYMBOL(netif_napi_add);
 
 void napi_disable(struct napi_struct *n)
 {
+       unsigned long val, new;
+
        might_sleep();
        set_bit(NAPI_STATE_DISABLE, &n->state);
 
-       while (test_and_set_bit(NAPI_STATE_SCHED, &n->state))
-               msleep(1);
-       while (test_and_set_bit(NAPI_STATE_NPSVC, &n->state))
-               msleep(1);
+       do {
+               val = READ_ONCE(n->state);
+               if (val & (NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC)) {
+                       usleep_range(20, 200);
+                       continue;
+               }
+
+               new = val | NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC;
+               new &= ~(NAPIF_STATE_THREADED | NAPIF_STATE_PREFER_BUSY_POLL);
+       } while (cmpxchg(&n->state, val, new) != val);
 
        hrtimer_cancel(&n->timer);
 
-       clear_bit(NAPI_STATE_PREFER_BUSY_POLL, &n->state);
        clear_bit(NAPI_STATE_DISABLE, &n->state);
-       clear_bit(NAPI_STATE_THREADED, &n->state);
 }
 EXPORT_SYMBOL(napi_disable);