Commit 0cc12a28 authored May 15, 2021 by Tiezhu Yang Committed by Greg Kroah-Hartman Jun 16, 2021

MIPS: Fix kernel hang under FUNCTION_GRAPH_TRACER and PREEMPT_TRACER



[ Upstream commit 78cf0eb926cb1abeff2106bae67752e032fe5f3e ]

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 f93a1a00 ("MIPS: Fix crash that occurs when function tracing
is enabled").

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent e84620e8

arch/mips/lib/mips-atomic.c

+6 −6

Original line number	Diff line number	Diff line
		@@ -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);