Message ID | 1443034678-1475-1-git-send-email-nhorman@redhat.com |
---|---|
State | Accepted, archived |
Delegated to: | David Miller |
Headers | show |
From: Neil Horman <nhorman@redhat.com> Date: Wed, 23 Sep 2015 14:57:58 -0400 > Drivers might call napi_disable while not holding the napi instance poll_lock. > In those instances, its possible for a race condition to exist between > poll_one_napi and napi_disable. That is to say, poll_one_napi only tests the > NAPI_STATE_SCHED bit to see if there is work to do during a poll, and as such > the following may happen: > > CPU0 CPU1 > ndo_tx_timeout napi_poll_dev > napi_disable poll_one_napi > test_and_set_bit (ret 0) > test_bit (ret 1) > reset adapter napi_poll_routine > > If the adapter gets a tx timeout without a napi instance scheduled, its possible > for the adapter to think it has exclusive access to the hardware (as the napi > instance is now scheduled via the napi_disable call), while the netpoll code > thinks there is simply work to do. The result is parallel hardware access > leading to corrupt data structures in the driver, and a crash. > > Additionaly, there is another, more critical race between netpoll and > napi_disable. The disabled napi state is actually identical to the scheduled > state for a given napi instance. The implication being that, if a napi instance > is disabled, a netconsole instance would see the napi state of the device as > having been scheduled, and poll it, likely while the driver was dong something > requiring exclusive access. In the case above, its fairly clear that not having > the rings in a state ready to be polled will cause any number of crashes. > > The fix should be pretty easy. netpoll uses its own bit to indicate that that > the napi instance is in a state of being serviced by netpoll (NAPI_STATE_NPSVC). > We can just gate disabling on that bit as well as the sched bit. That should > prevent netpoll from conducting a napi poll if we convert its set bit to a > test_and_set_bit operation to provide mutual exclusion > > Change notes: > V2) > Remove a trailing whtiespace > Resubmit with proper subject prefix > > V3) > Clean up spacing nits > > Signed-off-by: Neil Horman <nhorman@tuxdriver.com> > CC: "David S. Miller" <davem@davemloft.net> > CC: jmaxwell@redhat.com > Tested-by: jmaxwell@redhat.com Applied, thanks Neil. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index b791405..d2ffeaf 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -507,6 +507,7 @@ static inline void napi_enable(struct napi_struct *n) BUG_ON(!test_bit(NAPI_STATE_SCHED, &n->state)); smp_mb__before_atomic(); clear_bit(NAPI_STATE_SCHED, &n->state); + clear_bit(NAPI_STATE_NPSVC, &n->state); } #ifdef CONFIG_SMP diff --git a/net/core/dev.c b/net/core/dev.c index ee0d628..b6b01bf 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -4723,6 +4723,8 @@ void napi_disable(struct napi_struct *n) while (test_and_set_bit(NAPI_STATE_SCHED, &n->state)) msleep(1); + while (test_and_set_bit(NAPI_STATE_NPSVC, &n->state)) + msleep(1); hrtimer_cancel(&n->timer); diff --git a/net/core/netpoll.c b/net/core/netpoll.c index 6aa3db8..1734f50 100644 --- a/net/core/netpoll.c +++ b/net/core/netpoll.c @@ -142,7 +142,7 @@ static void queue_process(struct work_struct *work) */ static int poll_one_napi(struct napi_struct *napi, int budget) { - int work; + int work = 0; /* net_rx_action's ->poll() invocations and our's are * synchronized by this test which is only made while @@ -151,7 +151,13 @@ static int poll_one_napi(struct napi_struct *napi, int budget) if (!test_bit(NAPI_STATE_SCHED, &napi->state)) return budget; - set_bit(NAPI_STATE_NPSVC, &napi->state); + /* 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; work = napi->poll(napi, budget); WARN_ONCE(work > budget, "%pF exceeded budget in poll\n", napi->poll); @@ -159,6 +165,7 @@ static int poll_one_napi(struct napi_struct *napi, int budget) clear_bit(NAPI_STATE_NPSVC, &napi->state); +out: return budget - work; }