On Tue, Sep 22, 2015 at 02:00:23PM -0400, Neil Horman wrote: > 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 > > Signed-off-by: Neil Horman <nhor...@tuxdriver.com> > CC: "David S. Miller" <da...@davemloft.net> > CC: jmaxw...@redhat.com > Tested-by: jmaxw...@redhat.com > --- > include/linux/netdevice.h | 2 ++ > net/core/dev.c | 2 ++ > net/core/netpoll.c | 12 ++++++++++-- > 3 files changed, 14 insertions(+), 2 deletions(-) > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h > index b791405..48becac 100644 > --- a/include/linux/netdevice.h > +++ b/include/linux/netdevice.h > @@ -507,6 +507,8 @@ 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..91cf217 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 +151,14 @@ 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 +166,7 @@ static int poll_one_napi(struct napi_struct *napi, int > budget) > > clear_bit(NAPI_STATE_NPSVC, &napi->state); > > +out: > return budget - work; > } > > -- > 2.1.0 > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Shoot, I forgot to change my subject prefix, sorry about that. Dave this applies to net-next, shall I resubmit with a proper prefix, or are you good with it as is? Neil
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