netpoll: Drop budget parameter from NAPI polling call hierarchy

For some reason we were carrying the budget value around between the
various calls to napi->poll.  If for example one of the drivers called had
a bug in which it returned a non-zero value for work this could result in
the budget value becoming negative.

Rather than carry around a value of budget that is 0 or less we can instead
just loop through and pass 0 to each napi->poll call.  If any driver
returns a value for work done that is non-zero then we can report that
driver and continue rather than allowing a bad actor to make the budget
value negative and pass that negative value to napi->poll.

Note, the only actual change here is that instead of letting budget become
negative we are keeping it at 0 regardless of the value returned for work
since it should not be possible for the polling routine to do any actual
work with a budget of 0.  So if the polling routine returns a non-0 value
we are just reporting it and continuing with a budget of 0 rather than
letting that work value be subtracted from the budget of 0.

Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 8bdada242a7d1266fe276f86aa02bd1691d56697..94acfc89ad976da245bed577511bd7a1c079f6f5 100644 (file)
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -140,7 +140,7 @@ static void queue_process(struct work_struct *work)
  * case. Further, we test the poll_owner to avoid recursion on UP
  * systems where the lock doesn't exist.
  */
-static int poll_one_napi(struct napi_struct *napi, int budget)
+static void poll_one_napi(struct napi_struct *napi)
 {
        int work = 0;
 
@@ -149,33 +149,33 @@ static int poll_one_napi(struct napi_struct *napi, int budget)
         * holding the napi->poll_lock.
         */
        if (!test_bit(NAPI_STATE_SCHED, &napi->state))
-               return budget;
+               return;
 
        /* If we set this bit but see that it has already been set,
         * that indicates that napi has been disabled and we need
         * to abort this operation
         */
        if (test_and_set_bit(NAPI_STATE_NPSVC, &napi->state))
-               goto out;
+               return;
 
-       work = napi->poll(napi, budget);
-       WARN_ONCE(work > budget, "%pF exceeded budget in poll\n", napi->poll);
+       /* We explicilty pass the polling call a budget of 0 to
+        * indicate that we are clearing the Tx path only.
+        */
+       work = napi->poll(napi, 0);
+       WARN_ONCE(work, "%pF exceeded budget in poll\n", napi->poll);
        trace_napi_poll(napi);
 
        clear_bit(NAPI_STATE_NPSVC, &napi->state);
-
-out:
-       return budget - work;
 }
 
-static void poll_napi(struct net_device *dev, int budget)
+static void poll_napi(struct net_device *dev)
 {
        struct napi_struct *napi;
 
        list_for_each_entry(napi, &dev->napi_list, dev_list) {
                if (napi->poll_owner != smp_processor_id() &&
                    spin_trylock(&napi->poll_lock)) {
-                       budget = poll_one_napi(napi, budget);
+                       poll_one_napi(napi);
                        spin_unlock(&napi->poll_lock);
                }
        }
@@ -185,7 +185,6 @@ static void netpoll_poll_dev(struct net_device *dev)
 {
        const struct net_device_ops *ops;
        struct netpoll_info *ni = rcu_dereference_bh(dev->npinfo);
-       int budget = 0;
 
        /* Don't do any rx activity if the dev_lock mutex is held
         * the dev_open/close paths use this to block netpoll activity
@@ -208,7 +207,7 @@ static void netpoll_poll_dev(struct net_device *dev)
        /* Process pending work on NIC */
        ops->ndo_poll_controller(dev);
 
-       poll_napi(dev, budget);
+       poll_napi(dev);
 
        up(&ni->dev_lock);