[PATCH stable-4.9.y] locking/qspinlock: Pull in asm/byteorder.h to ensure correct endianness

[Will Deacon]

From: Dave Airlie <airlied@xxxxxxxxxx>

This commit is not required upstream, but is required for the 4.9.y
stable series.

Upstream commit 101110f6271c ("Kbuild: always define endianess in
kconfig.h") ensures that either __LITTLE_ENDIAN or __BIG_ENDIAN is
defined to reflect the endianness of the target CPU architecture
regardless of whether or not <asm/byteorder.h> has been #included. The
upstream definition of 'struct qspinlock' relies on this property.

Unfortunately, the 4.9.y stable series does not provide this guarantee,
so the 'spin_unlock()' routine can erroneously treat the underlying
lockword as big-endian on little-endian architectures using native
qspinlock (i.e. x86_64 without PV) if the caller has not included
<asm/byteorder.h>. This can lead to hangs such as the one in
'i915_gem_request()' reported via bugzilla:

  https://bugzilla.kernel.org/show_bug.cgi?id=202063

Fix the issue by ensuring that <asm/byteorder.h> is #included in
<asm/qspinlock_types.h>, where 'struct qspinlock' is defined.

Cc: <stable@xxxxxxxxxxxxxxx> # 4.9
Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx>
[will: wrote commit message]
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
---
 include/asm-generic/qspinlock_types.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/asm-generic/qspinlock_types.h b/include/asm-generic/qspinlock_types.h
index d10f1e7d6ba8..6503e96710fa 100644
--- a/include/asm-generic/qspinlock_types.h
+++ b/include/asm-generic/qspinlock_types.h
@@ -18,6 +18,8 @@
 #ifndef __ASM_GENERIC_QSPINLOCK_TYPES_H
 #define __ASM_GENERIC_QSPINLOCK_TYPES_H
 
+#include <asm/byteorder.h>
+
 /*
  * Including atomic.h with PARAVIRT on will cause compilation errors because
  * of recursive header file incluson via paravirt_types.h. So don't include
-- 
2.17.1