[PATCH -mm 0/1] signal: simplify set_user_sigmask/restore_user_sigmask

[Oleg Nesterov]

On top of

        
signal-remove-the-wrong-signal_pending-check-in-restore_user_sigmask.patch

Let me repeat, every file touched by this patch needs more cleanups,
fs/aio.c looks wrong with or without the recent changes. Lets discuss
this later.

To simplify the review, please see the code with this patch applied.
I am using epoll_pwait() as an example because it looks very simple.

Note that this patch moves WARN_ON(!TIF_SIGPENDING) from set_restore_sigmask()
to restore_unless().

        int set_user_sigmask(const sigset_t __user *umask, size_t sigsetsize)
        {
                sigset_t *kmask;

                if (!umask)
                        return 0;
                if (sigsetsize != sizeof(sigset_t))
                        return -EINVAL;
                if (copy_from_user(kmask, umask, sizeof(sigset_t)))
                        return -EFAULT;

                set_restore_sigmask();
                current->saved_sigmask = current->blocked;
                set_current_blocked(kmask);

                return 0;
        }

        static inline void restore_saved_sigmask_unless(bool interrupted)
        {
                if (interrupted)
                        WARN_ON(!test_thread_flag(TIF_SIGPENDING));
                else
                        restore_saved_sigmask();
        }

        SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, 
events,
                        int, maxevents, int, timeout, const sigset_t __user *, 
sigmask,
                        size_t, sigsetsize)
        {
                int error;

                /*
                 * If the caller wants a certain signal mask to be set during 
the wait,
                 * we apply it here.
                 */
                error = set_user_sigmask(sigmask, sigsetsize);
                if (error)
                        return error;

                error = do_epoll_wait(epfd, events, maxevents, timeout);
                restore_saved_sigmask_unless(error == -EINTR);

                return error;
        }

Oleg.