Patch "ARC: Call trace_hardirqs_on() before enabling irqs" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

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

    ARC: Call trace_hardirqs_on() before enabling irqs

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:
     arc-call-trace_hardirqs_on-before-enabling-irqs.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@vger.kernel.org> know about it.


>From 18b43e89d295cc65151c505c643c98fb2c320e59 Mon Sep 17 00:00:00 2001
From: Daniel Mentz <danielmentz@google.com>
Date: Thu, 4 Aug 2016 17:56:53 -0700
Subject: ARC: Call trace_hardirqs_on() before enabling irqs

From: Daniel Mentz <danielmentz@google.com>

commit 18b43e89d295cc65151c505c643c98fb2c320e59 upstream.

trace_hardirqs_on_caller() in lockdep.c expects to be called before, not
after interrupts are actually enabled.

The following comment in kernel/locking/lockdep.c substantiates this
claim:

"
/*
 * We're enabling irqs and according to our state above irqs weren't
 * already enabled, yet we find the hardware thinks they are in fact
 * enabled.. someone messed up their IRQ state tracing.
 */
"

An example can be found in include/linux/irqflags.h:

	do { trace_hardirqs_on(); raw_local_irq_enable(); } while (0)

Without this change, we hit the following DEBUG_LOCKS_WARN_ON.

[    7.760000] ------------[ cut here ]------------
[    7.760000] WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:2711 resume_user_mode_begin+0x48/0xf0
[    7.770000] DEBUG_LOCKS_WARN_ON(!irqs_disabled())
[    7.780000] Modules linked in:
[    7.780000] CPU: 0 PID: 1 Comm: init Not tainted 4.7.0-00003-gc668bb9-dirty #366
[    7.790000]
[    7.790000] Stack Trace:
[    7.790000]   arc_unwind_core.constprop.1+0xa4/0x118
[    7.800000]   warn_slowpath_fmt+0x72/0x158
[    7.800000]   resume_user_mode_begin+0x48/0xf0
[    7.810000] ---[ end trace 6f6a7a8fae20d2f0 ]---

Signed-off-by: Daniel Mentz <danielmentz@google.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/arc/include/asm/irqflags-compact.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arc/include/asm/irqflags-compact.h
+++ b/arch/arc/include/asm/irqflags-compact.h
@@ -188,10 +188,10 @@ static inline int arch_irqs_disabled(voi
 .endm
 
 .macro IRQ_ENABLE  scratch
+	TRACE_ASM_IRQ_ENABLE
 	lr	\scratch, [status32]
 	or	\scratch, \scratch, (STATUS_E1_MASK | STATUS_E2_MASK)
 	flag	\scratch
-	TRACE_ASM_IRQ_ENABLE
 .endm
 
 #endif	/* __ASSEMBLY__ */


Patches currently in stable-queue which might be from danielmentz@google.com are

queue-4.4/arc-call-trace_hardirqs_on-before-enabling-irqs.patch