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

Message ID 20190124185415.29830-1-will.deacon@arm.com
State New
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Series
  • [stable-4.9.y] locking/qspinlock: Pull in asm/byteorder.h to ensure correct endianness
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Commit Message

Will Deacon Jan. 24, 2019, 6:54 p.m.
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(+)

-- 
2.17.1

Comments

Greg Kroah-Hartman Jan. 24, 2019, 7:04 p.m. | #1
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
David Airlie Jan. 24, 2019, 7:14 p.m. | #2
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.

Patch

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