[PATCH 4.4 258/312] sfc: clear napi_hash state when copying channels

[Greg Kroah-Hartman]

From: Bert Kenward <bkenward@xxxxxxxxxxxxxx>

commit 46d054f8f540612f09987a53154aa39ae15f2e4c upstream.

efx_copy_channel() doesn't correctly clear the napi_hash related state.
This means that when napi_hash_add is called for that channel nothing is
done, and we are left with a copy of the napi_hash_node from the old
channel. When we later call napi_hash_del() on this channel we have a
stale napi_hash_node.

Corruption is only seen when there are multiple entries in one of the
napi_hash lists. This is made more likely by having a very large number
of channels. Testing was carried out with 512 channels - 32 channels on
each of 16 ports.

This failure typically appears as protection faults within napi_by_id()
or napi_hash_add(). efx_copy_channel() is only used when tx or rx ring
sizes are changed (ethtool -G).

Fixes: 36763266bbe8 ("sfc: Add support for busy polling")
Signed-off-by: Bert Kenward <bkenward@xxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/net/ethernet/sfc/efx.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/net/ethernet/sfc/efx.c
+++ b/drivers/net/ethernet/sfc/efx.c
@@ -479,6 +479,9 @@ efx_copy_channel(const struct efx_channe
 	*channel = *old_channel;
 
 	channel->napi_dev = NULL;
+	INIT_HLIST_NODE(&channel->napi_str.napi_hash_node);
+	channel->napi_str.napi_id = 0;
+	channel->napi_str.state = 0;
 	memset(&channel->eventq, 0, sizeof(channel->eventq));
 
 	for (j = 0; j < EFX_TXQ_TYPES; j++) {