linux-kernel - [PATCH 4.8 01/45] gro_cells: mark napi struct as not busy poll candidates

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Date:   Fri,  9 Dec 2016 17:20:30 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        Rolf Neugebauer <rolf.neugebauer@...ker.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.8 01/45] gro_cells: mark napi struct as not busy poll candidates

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@...gle.com>

[ 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.

Fixes: 93d05d4a320c ("net: provide generic busy polling to all NAPI drivers")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: Rolf Neugebauer <rolf.neugebauer@...ker.com>
Reported-by: Eric W. Biederman <ebiederm@...ssion.com>
Acked-by: Cong Wang <xiyou.wangcong@...il.com>
Tested-by: Rolf Neugebauer <rolf.neugebauer@...ker.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 include/net/gro_cells.h |    3 +++
 1 file changed, 3 insertions(+)

--- a/include/net/gro_cells.h
+++ b/include/net/gro_cells.h
@@ -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);
 	}