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netpoll: Drop budget parameter from NAPI polling call hierarchy

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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>
This commit is contained in:
Alexander Duyck 2015-09-28 09:16:17 -07:00 committed by David S. Miller
parent 2594e9064a
commit 822d54b9c2
1 changed files with 11 additions and 12 deletions
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23
net/core/netpoll.c
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@ -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);