From 590d25e7d72d525d63309d586bdb442818268a48 Mon Sep 17 00:00:00 2001
Message-Id: <590d25e7d72d525d63309d586bdb442818268a48.1592846147.git.zanussi@kernel.org>
In-Reply-To: <07cd0dbc80b976663c80755496a03f288decfe5a.1592846146.git.zanussi@kernel.org>
References: <07cd0dbc80b976663c80755496a03f288decfe5a.1592846146.git.zanussi@kernel.org>
From: Steven Rostedt <rostedt@goodmis.org>
Date: Tue, 6 Dec 2016 17:50:30 -0500
Subject: [PATCH 204/330] net: Have __napi_schedule_irqoff() disable interrupts
 on RT
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.127-rt55.tar.xz

A customer hit a crash where the napi sd->poll_list became corrupted.
The customer had the bnx2x driver, which does a
__napi_schedule_irqoff() in its interrupt handler. Unfortunately, when
running with CONFIG_PREEMPT_RT_FULL, this interrupt handler is run as a
thread and is preemptable. The call to ____napi_schedule() must be done
with interrupts disabled to protect the per cpu softnet_data's
"poll_list, which is protected by disabling interrupts (disabling
preemption is enough when all interrupts are threaded and
local_bh_disable() can't preempt)."

As bnx2x isn't the only driver that does this, the safest thing to do
is to make __napi_schedule_irqoff() call __napi_schedule() instead when
CONFIG_PREEMPT_RT_FULL is enabled, which will call local_irq_save()
before calling ____napi_schedule().

Cc: stable-rt@vger.kernel.org
Signed-off-by: Steven Rostedt (Red Hat) <rostedt@goodmis.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/netdevice.h | 12 ++++++++++++
 net/core/dev.c            |  2 ++
 2 files changed, 14 insertions(+)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 5de4b66e11fe..1d6bb0ab437f 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -422,7 +422,19 @@ typedef enum rx_handler_result rx_handler_result_t;
 typedef rx_handler_result_t rx_handler_func_t(struct sk_buff **pskb);
 
 void __napi_schedule(struct napi_struct *n);
+
+/*
+ * When PREEMPT_RT_FULL is defined, all device interrupt handlers
+ * run as threads, and they can also be preempted (without PREEMPT_RT
+ * interrupt threads can not be preempted). Which means that calling
+ * __napi_schedule_irqoff() from an interrupt handler can be preempted
+ * and can corrupt the napi->poll_list.
+ */
+#ifdef CONFIG_PREEMPT_RT_FULL
+#define __napi_schedule_irqoff(n) __napi_schedule(n)
+#else
 void __napi_schedule_irqoff(struct napi_struct *n);
+#endif
 
 static inline bool napi_disable_pending(struct napi_struct *n)
 {
diff --git a/net/core/dev.c b/net/core/dev.c
index 52d44a4db2ff..c67056ad032b 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5951,6 +5951,7 @@ bool napi_schedule_prep(struct napi_struct *n)
 }
 EXPORT_SYMBOL(napi_schedule_prep);
 
+#ifndef CONFIG_PREEMPT_RT_FULL
 /**
  * __napi_schedule_irqoff - schedule for receive
  * @n: entry to schedule
@@ -5962,6 +5963,7 @@ void __napi_schedule_irqoff(struct napi_struct *n)
 	____napi_schedule(this_cpu_ptr(&softnet_data), n);
 }
 EXPORT_SYMBOL(__napi_schedule_irqoff);
+#endif
 
 bool napi_complete_done(struct napi_struct *n, int work_done)
 {
-- 
2.17.1

