On s390 user space is a separate address space, so access_ok() has nothing to check, and get_user() and put_user() are __get_user() and __put_user() plus might_fault(). The remaining callers can use the normal accessors directly: - signal frame setup writes the back chain, the signal number and the ucontext header in process context; - the user stack walker for stack traces and perf callchains already runs under pagefault_disable(), where might_fault() returns early; - the general register set writer for ptrace runs in the tracer's process context with no locks held. This is part of getting rid of __get_user() and __put_user() entirely. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>