Adjust conditions in on_stack function. That fixes backchain unwinder
which was unable to read pt_regs at the very bottom of the stack and
hence couldn't follow stacks (e.g. from async stack to a task stack).
Fixes: 78c98f9074 ("s390/unwind: introduce stack unwind API")
Reported-by: Julian Wiedmann <[email protected]>
Reviewed-by: Heiko Carstens <[email protected]>
Signed-off-by: Vasily Gorbik <[email protected]>
Signed-off-by: Heiko Carstens <[email protected]>