On Thu, Jan 24, 2019 at 06:54:15PM +0000, Will Deacon wrote:
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.
That is crazy...
Thanks for the patch, now queued up.
greg k-h