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Subject[PATCH 4.13 13/85] parisc: Fix double-word compare and exchange in LWS code on 32-bit kernels
Date
4.13-stable review patch.  If anyone has any objections, please let me know.

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

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

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