Patch "MIPS: Fix kernel hang under FUNCTION_GRAPH_TRACER and PREEMPT_TRACER" has been added to the 4.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    MIPS: Fix kernel hang under FUNCTION_GRAPH_TRACER and PREEMPT_TRACER

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mips-fix-kernel-hang-under-function_graph_tracer-and.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit c829fcb804d606ebcc2f80ad0cdf066d9071f1e1
Author: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
Date:   Sat May 15 19:02:01 2021 +0800

    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 f93a1a00f2bd ("MIPS: Fix crash that occurs when function tracing
    is enabled").
    
    Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
    Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
    Signed-off-by: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/mips/lib/mips-atomic.c b/arch/mips/lib/mips-atomic.c
index 272af8ac2425..fd50aa7b178a 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);
 
@@ -62,7 +62,7 @@ notrace unsigned long arch_local_irq_save(void)
 {
 	unsigned long flags;
 
-	preempt_disable();
+	preempt_disable_notrace();
 
 	__asm__ __volatile__(
 	"	.set	push						\n"
@@ -79,7 +79,7 @@ notrace unsigned long arch_local_irq_save(void)
 	: /* no inputs */
 	: "memory");
 
-	preempt_enable();
+	preempt_enable_notrace();
 
 	return flags;
 }
@@ -89,7 +89,7 @@ notrace void arch_local_irq_restore(unsigned long flags)
 {
 	unsigned long __tmp1;
 
-	preempt_disable();
+	preempt_disable_notrace();
 
 	__asm__ __volatile__(
 	"	.set	push						\n"
@@ -107,7 +107,7 @@ notrace void arch_local_irq_restore(unsigned long flags)
 	: "0" (flags)
 	: "memory");
 
-	preempt_enable();
+	preempt_enable_notrace();
 }
 EXPORT_SYMBOL(arch_local_irq_restore);