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authorNeil Horman <nhorman@redhat.com>2015-09-23 14:57:58 -0400
committerDavid S. Miller <davem@davemloft.net>2015-09-23 14:32:50 -0700
commit2d8bff12699abc3a9bf886bb0b79f44d94d81496 (patch)
treef694b97b2ced5e50327215366fd63d7cd0dd42fd /include
parent675ee231d960af2af3606b4480324e26797eb010 (diff)
netpoll: Close race condition between poll_one_napi and napi_disable
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 Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include')
-rw-r--r--include/linux/netdevice.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 88a00694eda5..2d15e3831440 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

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