Commit 822d54b9 authored by Alexander Duyck's avatar Alexander Duyck Committed by David S. Miller
Browse files

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: default avatarAlexander Duyck <aduyck@mirantis.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 2594e906

net/core/netpoll.c

+11 −12
Original line number Diff line number Diff line
@@ -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);

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