Patch "gro_cells: mark napi struct as not busy poll candidates" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

gro_cells: mark napi struct as not busy poll candidates

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
gro_cells-mark-napi-struct-as-not-busy-poll-candidates.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Mon, 14 Nov 2016 16:28:42 -0800
Subject: gro_cells: mark napi struct as not busy poll candidates

From: Eric Dumazet <[email protected]>

[ Upstream commit e88a2766143a27bfe6704b4493b214de4094cf29 ]

Rolf Neugebauer reported very long delays at netns dismantle.

Eric W. Biederman was kind enough to look at this problem and noticed synchronize_net() occurring from netif_napi_del() that was added in linux-4.5

Busy polling makes no sense for tunnels NAPI.
If busy poll is used for sessions over tunnels, the poller will need to poll the physical device queue anyway.

netif_tx_napi_add() could be used here, but function name is misleading, and renaming it is not stable material, so set NAPI_STATE_NO_BUSY_POLL bit directly.

This will avoid inserting gro_cells napi structures in napi_hash[] and avoid the problematic synchronize_net() (per possible cpu) that Rolf reported.

---
 include/net/gro_cells.h |    3 +++
 1 file changed, 3 insertions(+)

@@ -68,6 +68,9 @@ static inline int gro_cells_init(struct
 		struct gro_cell *cell = per_cpu_ptr(gcells->cells, i);
 
 		__skb_queue_head_init(&cell->napi_skbs);
+
+		set_bit(NAPI_STATE_NO_BUSY_POLL, &cell->napi.state);
+
 		netif_napi_add(dev, &cell->napi, gro_cell_poll, 64);
 		napi_enable(&cell->napi);
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/ipv4-fix-memory-leak-in-exception-case-for-splitting-tries.patch queue-4.8/virtio-net-add-a-missing-synchronize_net.patch queue-4.8/gro_cells-mark-napi-struct-as-not-busy-poll-candidates.patch queue-4.8/udplite-call-proper-backlog-handlers.patch queue-4.8/ip6_offload-check-segs-for-null-in-ipv6_gso_segment.patch queue-4.8/ipv4-restore-fib_trie_flush_external-function-and-fix-call-ordering.patch queue-4.8/net-dccp-fix-use-after-free-in-dccp_invalid_packet.patch queue-4.8/net-avoid-signed-overflows-for-so_-snd-rcv-bufforce.patch queue-4.8/packet-fix-race-condition-in-packet_set_ring.patch