Patch "arm64: cmpxchg_dbl: fix return value type" has been added to the 4.3-stable tree

[<gregkh@linuxfoundation.org>]

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

    arm64: cmpxchg_dbl: fix return value type

to the 4.3-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:
     arm64-cmpxchg_dbl-fix-return-value-type.patch
and it can be found in the queue-4.3 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 57a65667991aaddef730b0c910111ab76a1ff245 Mon Sep 17 00:00:00 2001
From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Date: Thu, 5 Nov 2015 14:00:56 +0000
Subject: arm64: cmpxchg_dbl: fix return value type

From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

commit 57a65667991aaddef730b0c910111ab76a1ff245 upstream.

The current arm64 __cmpxchg_double{_mb} implementations carry out the
compare exchange by first comparing the old values passed in to the
values read from the pointer provided and by stashing the cumulative
bitwise difference in a 64-bit register.

By comparing the register content against 0, it is possible to detect if
the values read differ from the old values passed in, so that the compare
exchange detects whether it has to bail out or carry on completing the
operation with the exchange.

Given the current implementation, to detect the cmpxchg operation
status, the __cmpxchg_double{_mb} functions should return the 64-bit
stashed bitwise difference so that the caller can detect cmpxchg failure
by comparing the return value content against 0. The current implementation
declares the return value as an int, which means that the 64-bit
value stashing the bitwise difference is truncated before being
returned to the __cmpxchg_double{_mb} callers, which means that
any bitwise difference present in the top 32 bits goes undetected,
triggering false positives and subsequent kernel failures.

This patch fixes the issue by declaring the arm64 __cmpxchg_double{_mb}
return values as a long, so that the bitwise difference is
properly propagated on failure, restoring the expected behaviour.

Fixes: e9a4b795652f ("arm64: cmpxchg_dbl: patch in lse instructions when supported by the CPU")
Cc: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/arm64/include/asm/atomic_ll_sc.h |    2 +-
 arch/arm64/include/asm/atomic_lse.h   |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

--- a/arch/arm64/include/asm/atomic_ll_sc.h
+++ b/arch/arm64/include/asm/atomic_ll_sc.h
@@ -211,7 +211,7 @@ __CMPXCHG_CASE( ,  , mb_8, dmb ish, l, "
 #undef __CMPXCHG_CASE
 
 #define __CMPXCHG_DBL(name, mb, rel, cl)				\
-__LL_SC_INLINE int							\
+__LL_SC_INLINE long							\
 __LL_SC_PREFIX(__cmpxchg_double##name(unsigned long old1,		\
 				      unsigned long old2,		\
 				      unsigned long new1,		\
--- a/arch/arm64/include/asm/atomic_lse.h
+++ b/arch/arm64/include/asm/atomic_lse.h
@@ -348,7 +348,7 @@ __CMPXCHG_CASE(x,  , mb_8, al, "memory")
 #define __LL_SC_CMPXCHG_DBL(op)	__LL_SC_CALL(__cmpxchg_double##op)
 
 #define __CMPXCHG_DBL(name, mb, cl...)					\
-static inline int __cmpxchg_double##name(unsigned long old1,		\
+static inline long __cmpxchg_double##name(unsigned long old1,		\
 					 unsigned long old2,		\
 					 unsigned long new1,		\
 					 unsigned long new2,		\


Patches currently in stable-queue which might be from lorenzo.pieralisi@arm.com are

queue-4.3/arm64-kernel-pause-unpause-function-graph-tracer-in-cpu_suspend.patch
queue-4.3/arm64-kernel-enforce-pmuserenr_el0-initialization-and-restore.patch
queue-4.3/arm64-cmpxchg_dbl-fix-return-value-type.patch