parisc: Fix double-word compare and exchange in LWS code on 32-bit kernels

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@bell.net>
Tested-by: Christoph Biedl <debian.axhn@manchmal.in-ulm.de>
Fixes: 89206491201c ("parisc: Implement new LWS CAS supporting 64 bit operations.")
Cc: stable@vger.kernel.org # 3.13+
Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/arch/parisc/kernel/syscall.S b/arch/parisc/kernel/syscall.S
index 23de307c3052aa9ecac21fd6c294657fb53de447..41e60a9c7db23b8384b18bf8ddd45f188ef4a0c3 100644 (file)
--- a/arch/parisc/kernel/syscall.S
+++ b/arch/parisc/kernel/syscall.S
@@ -742,7 +742,7 @@ 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 */
@@ -834,11 +834,11 @@ 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 */