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

stable inclusion
from stable-v5.10.164
commit 51dbedee2ff3b000c9905189e33e1972b6c9f649
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7T7G4

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=51dbedee2ff3b000c9905189e33e1972b6c9f649



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

commit e3f360db upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>