From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Sat, 27 May 2017 19:02:06 +0200
Subject: net/core: disable NET_RX_BUSY_POLL
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/wagi/linux-stable-rt.git
Git-commit: 8cdccfd6e7ecd408d2d595af6a9d768fdce6f40e
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

sk_busy_loop() does preempt_disable() followed by a few operations which can
take sleeping locks and may get long.
I _think_ that we could use preempt_disable_nort() (in sk_busy_loop()) instead
but after a successfull cmpxchg(&napi->state, …) we would gain the ressource
and could be scheduled out. At this point nobody knows who (which context) owns
it and so it could take a while until the state is realeased and napi_poll()
could be invoked again.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Daniel Wagner <dwagner@suse.de>
---
 net/Kconfig |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/Kconfig
+++ b/net/Kconfig
@@ -278,7 +278,7 @@ config CGROUP_NET_CLASSID
 
 config NET_RX_BUSY_POLL
 	bool
-	default y
+	default y if !PREEMPT_RT
 
 config BQL
 	bool