[PATCH 4.14 034/109] nfp: avoid soft lockups under control message storm

[Greg Kroah-Hartman]

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

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

From: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>

[ Upstream commit ff58e2df62ce29d0552278c290ae494b30fe0c6f ]

When FW floods the driver with control messages try to exit the cmsg
processing loop every now and then to avoid soft lockups.  Cmsg
processing is generally very lightweight so 512 seems like a reasonable
budget, which should not be exceeded under normal conditions.

Fixes: 77ece8d5f196 ("nfp: add control vNIC datapath")
Signed-off-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxxx>
Tested-by: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@xxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/ethernet/netronome/nfp/nfp_net_common.c |   17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

--- a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
+++ b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
@@ -2058,14 +2058,17 @@ nfp_ctrl_rx_one(struct nfp_net *nn, stru
 	return true;
 }
 
-static void nfp_ctrl_rx(struct nfp_net_r_vector *r_vec)
+static bool nfp_ctrl_rx(struct nfp_net_r_vector *r_vec)
 {
 	struct nfp_net_rx_ring *rx_ring = r_vec->rx_ring;
 	struct nfp_net *nn = r_vec->nfp_net;
 	struct nfp_net_dp *dp = &nn->dp;
+	unsigned int budget = 512;
 
-	while (nfp_ctrl_rx_one(nn, dp, r_vec, rx_ring))
+	while (nfp_ctrl_rx_one(nn, dp, r_vec, rx_ring) && budget--)
 		continue;
+
+	return budget;
 }
 
 static void nfp_ctrl_poll(unsigned long arg)
@@ -2077,9 +2080,13 @@ static void nfp_ctrl_poll(unsigned long
 	__nfp_ctrl_tx_queued(r_vec);
 	spin_unlock_bh(&r_vec->lock);
 
-	nfp_ctrl_rx(r_vec);
-
-	nfp_net_irq_unmask(r_vec->nfp_net, r_vec->irq_entry);
+	if (nfp_ctrl_rx(r_vec)) {
+		nfp_net_irq_unmask(r_vec->nfp_net, r_vec->irq_entry);
+	} else {
+		tasklet_schedule(&r_vec->tasklet);
+		nn_dp_warn(&r_vec->nfp_net->dp,
+			   "control message budget exceeded!\n");
+	}
 }
 
 /* Setup and Configuration