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From:   Tiezhu Yang <yangtiezhu@loongson.cn>
To:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc:     linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
        Xuefeng Li <lixuefeng@loongson.cn>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: [PATCH 2/2] MIPS: Fix kernel hang under FUNCTION_GRAPH_TRACER and PREEMPT_TRACER
Date:   Sat, 15 May 2021 19:02:01 +0800
Message-Id: <1621076521-22412-3-git-send-email-yangtiezhu@loongson.cn>
In-Reply-To: <1621076521-22412-1-git-send-email-yangtiezhu@loongson.cn>
References: <1621076521-22412-1-git-send-email-yangtiezhu@loongson.cn>
Precedence: bulk

When update the latest mainline kernel with the following three configs,
the kernel hangs during startup:

(1) CONFIG_FUNCTION_GRAPH_TRACER=y
(2) CONFIG_PREEMPT_TRACER=y
(3) CONFIG_FTRACE_STARTUP_TEST=y

When update the latest mainline kernel with the above two configs (1)
and (2), the kernel starts normally, but it still hangs when execute
the following command:

echo "function_graph" > /sys/kernel/debug/tracing/current_tracer

Without CONFIG_PREEMPT_TRACER=y, the above two kinds of kernel hangs
disappeared, so it seems that CONFIG_PREEMPT_TRACER has some influences
with function_graph tracer at the first glance.

I use ejtag to find out the epc address is related with preempt_enable()
in the file arch/mips/lib/mips-atomic.c, because function tracing can
trace the preempt_{enable,disable} calls that are traced, replace them
with preempt_{enable,disable}_notrace to prevent function tracing from
going into an infinite loop, and then it can fix the kernel hang issue.

By the way, it seems that this commit is a complement and improvement of
commit f93a1a00f2bd ("MIPS: Fix crash that occurs when function tracing
is enabled").

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Steven Rostedt <rostedt@goodmis.org>
---
 arch/mips/lib/mips-atomic.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/mips/lib/mips-atomic.c b/arch/mips/lib/mips-atomic.c
index de03838..a9b72ea 100644
--- a/arch/mips/lib/mips-atomic.c
+++ b/arch/mips/lib/mips-atomic.c
@@ -37,7 +37,7 @@
  */
 notrace void arch_local_irq_disable(void)
 {
-	preempt_disable();
+	preempt_disable_notrace();
 
 	__asm__ __volatile__(
 	"	.set	push						\n"
@@ -53,7 +53,7 @@ notrace void arch_local_irq_disable(void)
 	: /* no inputs */
 	: "memory");
 
-	preempt_enable();
+	preempt_enable_notrace();
 }
 EXPORT_SYMBOL(arch_local_irq_disable);
 
@@ -61,7 +61,7 @@ notrace unsigned long arch_local_irq_save(void)
 {
 	unsigned long flags;
 
-	preempt_disable();
+	preempt_disable_notrace();
 
 	__asm__ __volatile__(
 	"	.set	push						\n"
@@ -78,7 +78,7 @@ notrace unsigned long arch_local_irq_save(void)
 	: /* no inputs */
 	: "memory");
 
-	preempt_enable();
+	preempt_enable_notrace();
 
 	return flags;
 }
@@ -88,7 +88,7 @@ notrace void arch_local_irq_restore(unsigned long flags)
 {
 	unsigned long __tmp1;
 
-	preempt_disable();
+	preempt_disable_notrace();
 
 	__asm__ __volatile__(
 	"	.set	push						\n"
@@ -106,7 +106,7 @@ notrace void arch_local_irq_restore(unsigned long flags)
 	: "0" (flags)
 	: "memory");
 
-	preempt_enable();
+	preempt_enable_notrace();
 }
 EXPORT_SYMBOL(arch_local_irq_restore);
 
-- 
2.1.0