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

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

[Will Deacon]

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>
---
 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

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

[Greg KH]

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

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

[David Airlie]

On Fri, Jan 25, 2019 at 5:04 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> 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...

You've no idea, we've spent a couple of days at LCA figuring it all out :-)

Dave.