linux-kernel - [PATCH 4.4 26/27] parisc: Fix double-word compare and exchange in LWS code on 32-bit kernels

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Date:   Tue, 24 Oct 2017 14:58:11 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, John David Anglin <dave.anglin@...l.net>,
        Christoph Biedl <debian.axhn@...chmal.in-ulm.de>,
        Helge Deller <deller@....de>
Subject: [PATCH 4.4 26/27] parisc: Fix double-word compare and exchange in LWS code on 32-bit kernels

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

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

From: John David Anglin <dave.anglin@...l.net>

commit 374b3bf8e8b519f61eb9775888074c6e46b3bf0c upstream.

As discussed on the debian-hppa list, double-wordcompare and exchange
operations fail on 32-bit kernels.  Looking at the code, I realized that
the ",ma" completer does the wrong thing in the  "ldw,ma  4(%r26), %r29"
instruction.  This increments %r26 and causes the following store to
write to the wrong location.

Note by Helge Deller:
The patch applies cleanly to stable kernel series if this upstream
commit is merged in advance:
f4125cfdb300 ("parisc: Avoid trashing sr2 and sr3 in LWS code").

Signed-off-by: John David Anglin <dave.anglin@...l.net>
Tested-by: Christoph Biedl <debian.axhn@...chmal.in-ulm.de>
Fixes: 89206491201c ("parisc: Implement new LWS CAS supporting 64 bit operations.")
Signed-off-by: Helge Deller <deller@....de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/parisc/kernel/syscall.S |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/arch/parisc/kernel/syscall.S
+++ b/arch/parisc/kernel/syscall.S
@@ -740,7 +740,7 @@ lws_compare_and_swap_2:
 10:	ldd	0(%r25), %r25
 11:	ldd	0(%r24), %r24
 #else
-	/* Load new value into r22/r23 - high/low */
+	/* Load old value into r22/r23 - high/low */
 10:	ldw	0(%r25), %r22
 11:	ldw	4(%r25), %r23
 	/* Load new value into fr4 for atomic store later */
@@ -832,11 +832,11 @@ cas2_action:
 	copy	%r0, %r28
 #else
 	/* Compare first word */
-19:	ldw,ma	0(%r26), %r29
+19:	ldw	0(%r26), %r29
 	sub,=	%r29, %r22, %r0
 	b,n	cas2_end
 	/* Compare second word */
-20:	ldw,ma	4(%r26), %r29
+20:	ldw	4(%r26), %r29
 	sub,=	%r29, %r23, %r0
 	b,n	cas2_end
 	/* Perform the store */