netdev - [PATCH net] net: reduce RECURSION

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Message-Id: <1452188453-5523-1-git-send-email-hannes@stressinduktion.org>
Date:	Thu,  7 Jan 2016 18:40:53 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	netdev@...r.kernel.org
Cc:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net] net: reduce RECURSION_LIMIT to 8

When RECURSION_LIMIT was first introduced, Eric proposed a limit of 3.
This limit was later raised to 10 by DaveM. Nowadays it is observed that
configuraion errors in openvswitch cause the STACK_END_MAGIC to be
overwritten shortly after 9 recursion.

This patch tries to be conservative and reduces the limit to 8 without
further measurements. It seems ovs uses the stack more than other parts
of the networking stack - I couldn't bring the system down with a non-ovs
tunneling setup.

Cc: David S. Miller <davem@...emloft.net>
Cc: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
---
I don't do crazy run-time estimation of the stack size for one recursion
and try automatically to come up with a limit per arch or kconfig
settings, as I assume that all systems should behave the same regarding
the recursion maximum. All configurations should run on all kinds of
systems. I consider 8 recursions to be plenty enough for the time being.

 net/core/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index ae00b894e67555..d93da7df84325d 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2941,7 +2941,7 @@ static void skb_update_prio(struct sk_buff *skb)
 DEFINE_PER_CPU(int, xmit_recursion);
 EXPORT_SYMBOL(xmit_recursion);
 
-#define RECURSION_LIMIT 10
+#define RECURSION_LIMIT 8
 
 /**
  *	dev_loopback_xmit - loop back @skb
-- 
2.5.0