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    Subject[PATCH 4.9 39/39] locking/qspinlock: Pull in asm/byteorder.h to ensure correct endianness
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

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

    From: Dave Airlie <airlied@redhat.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@vger.kernel.org> # 4.9
    Signed-off-by: Dave Airlie <airlied@redhat.com>
    [will: wrote commit message]
    Signed-off-by: Will Deacon <will.deacon@arm.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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

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