From: Neil Horman <nhor...@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 <nhor...@tuxdriver.com> > CC: "David S. Miller" <da...@davemloft.net> > CC: jmaxw...@redhat.com > Tested-by: jmaxw...@redhat.com Applied, thanks Neil. -- 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
