s390/percpu: add READ_ONCE() to arch_this_cpu_to_op_simple()

Make sure that *ptr__ within arch_this_cpu_to_op_simple() is only
dereferenced once by using READ_ONCE(). Otherwise the compiler could
generate incorrect code.

Cc: <stable@vger.kernel.org>
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

diff --git a/arch/s390/include/asm/percpu.h b/arch/s390/include/asm/percpu.h
index cb5fc06904354a2e1cb523e826f02c1d171f7f55..081837b391e353a4467b194719671e4bd435e3a9 100644 (file)
--- a/arch/s390/include/asm/percpu.h
+++ b/arch/s390/include/asm/percpu.h
@@ -31,7 +31,7 @@
        pcp_op_T__ *ptr__;                                              \
        preempt_disable_notrace();                                      \
        ptr__ = raw_cpu_ptr(&(pcp));                                    \
-       prev__ = *ptr__;                                                \
+       prev__ = READ_ONCE(*ptr__);                                     \
        do {                                                            \
                old__ = prev__;                                         \
                new__ = old__ op (val);                                 \