1 files changed, 42 insertions, 0 deletions
diff --git a/debian/patches-rt/0238-net-dev-always-take-qdisc-s-busylock-in-__dev_xmit_s.patch b/debian/patches-rt/0238-net-dev-always-take-qdisc-s-busylock-in-__dev_xmit_s.patch
new file mode 100644
index 000000000..fe05e1e78
--- /dev/null
+++ b/debian/patches-rt/0238-net-dev-always-take-qdisc-s-busylock-in-__dev_xmit_s.patch
@@ -0,0 +1,42 @@
+From 3a7ff2036ac29effdf8fc39fc7ea9610f98ca5e4 Mon Sep 17 00:00:00 2001
+From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Date: Wed, 30 Mar 2016 13:36:29 +0200
+Subject: [PATCH 238/323] net: dev: always take qdisc's busylock in
+ __dev_xmit_skb()
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz
+
+The root-lock is dropped before dev_hard_start_xmit() is invoked and after
+setting the __QDISC___STATE_RUNNING bit. If this task is now pushed away
+by a task with a higher priority then the task with the higher priority
+won't be able to submit packets to the NIC directly instead they will be
+enqueued into the Qdisc. The NIC will remain idle until the task(s) with
+higher priority leave the CPU and the task with lower priority gets back
+and finishes the job.
+
+If we take always the busylock we ensure that the RT task can boost the
+low-prio task and submit the packet.
+
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ net/core/dev.c | 4 ++++
+ 1 file changed, 4 insertions(+)
+
+diff --git a/net/core/dev.c b/net/core/dev.c
+index c55993848233..c3b4e5e320ca 100644
+--- a/net/core/dev.c
++++ b/net/core/dev.c
+@@ -3796,7 +3796,11 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
+ 	 * This permits qdisc->running owner to get the lock more
+ 	 * often and dequeue packets faster.
+ 	 */
++#ifdef CONFIG_PREEMPT_RT
++	contended = true;
++#else
+ 	contended = qdisc_is_running(q);
++#endif
+ 	if (unlikely(contended))
+ 		spin_lock(&q->busylock);
+ 
+-- 
+2.43.0
+