netdev - [PATCH net] net, neigh: Set lower cap for neigh_managed

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Message-Id: <3b8c5aa906c52c3a8c995d1b2e8ccf650ea7c716.1653432794.git.daniel@iogearbox.net>
Date:   Wed, 25 May 2022 00:56:18 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     kuba@...nel.org
Cc:     wangyuweihx@...il.com, pabeni@...hat.com, netdev@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>,
        Nikolay Aleksandrov <razor@...ckwall.org>
Subject: [PATCH net] net, neigh: Set lower cap for neigh_managed_work rearming

Yuwei reported that plain reuse of DELAY_PROBE_TIME to rearm work queue
in neigh_managed_work is problematic if user explicitly configures the
DELAY_PROBE_TIME to 0 for a neighbor table. Such misconfig can then hog
CPU to 100% processing the system work queue. Instead, set lower interval
bound to HZ which is totally sufficient. Yuwei is additionally looking
into making the interval separately configurable from DELAY_PROBE_TIME.

Reported-by: Yuwei Wang <wangyuweihx@...il.com>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Cc: Nikolay Aleksandrov <razor@...ckwall.org>
Link: https://lore.kernel.org/netdev/797c3c53-ce1b-9f60-e253-cda615788f4a@iogearbox.net
---
 net/core/neighbour.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index f64ebd050f6..fd69133dc7c 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1579,7 +1579,7 @@ static void neigh_managed_work(struct work_struct *work)
 	list_for_each_entry(neigh, &tbl->managed_list, managed_list)
 		neigh_event_send_probe(neigh, NULL, false);
 	queue_delayed_work(system_power_efficient_wq, &tbl->managed_work,
-			   NEIGH_VAR(&tbl->parms, DELAY_PROBE_TIME));
+			   max(NEIGH_VAR(&tbl->parms, DELAY_PROBE_TIME), HZ));
 	write_unlock_bh(&tbl->lock);
 }
 
-- 
2.21.0