linux-kernel - [PATCH 4.9 39/39] locking/qspinlock: Pull in asm/byteorder.h to ensure correct endianness

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Message-Id: <20190124190449.768201183@linuxfoundation.org>
Date:   Thu, 24 Jan 2019 20:20:42 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dave Airlie <airlied@...hat.com>,
        Will Deacon <will.deacon@....com>
Subject: [PATCH 4.9 39/39] locking/qspinlock: Pull in asm/byteorder.h to ensure correct endianness

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dave Airlie <airlied@...hat.com>

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@...r.kernel.org> # 4.9
Signed-off-by: Dave Airlie <airlied@...hat.com>
[will: wrote commit message]
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 include/asm-generic/qspinlock_types.h |    2 ++
 1 file changed, 2 insertions(+)

--- 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