signal: introduce do_sigtimedwait() to factor out compat/native code

Factor out the common code in sys_rt_sigtimedwait/compat_sys_rt_sigtimedwait
to the new helper, do_sigtimedwait().

Add the comment to document the extra tick we add to timespec_to_jiffies(ts),
thanks to Linus who explained this to me.

Perhaps it would be better to move compat_sys_rt_sigtimedwait() into
signal.c under CONFIG_COMPAT, then we can make do_sigtimedwait() static.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Matt Fleming <matt.fleming@linux.intel.com>

include/linux/signal.h

@@ -242,6 +242,8 @@ extern int __group_send_sig_info(int, struct siginfo *, struct task_struct *);
 extern long do_rt_tgsigqueueinfo(pid_t tgid, pid_t pid, int sig,
 				 siginfo_t *info);
 extern long do_sigpending(void __user *, unsigned long);
+extern int do_sigtimedwait(const sigset_t *, siginfo_t *,
+				const struct timespec *);
 extern int sigprocmask(int, sigset_t *, sigset_t *);
 extern void set_current_blocked(const sigset_t *);
 extern int show_unhandled_signals;

kernel/compat.c

@@ -890,10 +890,9 @@ compat_sys_rt_sigtimedwait (compat_sigset_t __user *uthese,
 {
 	compat_sigset_t s32;
 	sigset_t s;
-	int sig;
 	struct timespec t;
 	siginfo_t info;
-	long ret, timeout;
+	long ret;
 
 	if (sigsetsize != sizeof(sigset_t))
 		return -EINVAL;
@@ -901,45 +900,19 @@ compat_sys_rt_sigtimedwait (compat_sigset_t __user *uthese,
 	if (copy_from_user(&s32, uthese, sizeof(compat_sigset_t)))
 		return -EFAULT;
 	sigset_from_compat(&s, &s32);
-	sigdelsetmask(&s,sigmask(SIGKILL)|sigmask(SIGSTOP));
-	signotset(&s);
 
-	timeout = MAX_SCHEDULE_TIMEOUT;
 	if (uts) {
-		if (get_compat_timespec (&t, uts))
+		if (get_compat_timespec(&t, uts))
 			return -EFAULT;
-		if (!timespec_valid(&t))
-			return -EINVAL;
-		timeout = timespec_to_jiffies(&t) + (t.tv_sec || t.tv_nsec);
 	}
 
-	spin_lock_irq(&current->sighand->siglock);
-	sig = dequeue_signal(current, &s, &info);
-	if (!sig && timeout) {
-		current->real_blocked = current->blocked;
-		sigandsets(&current->blocked, &current->blocked, &s);
-		recalc_sigpending();
-		spin_unlock_irq(&current->sighand->siglock);
-
-		timeout = schedule_timeout_interruptible(timeout);
-
-		spin_lock_irq(&current->sighand->siglock);
-		sig = dequeue_signal(current, &s, &info);
-		current->blocked = current->real_blocked;
-		siginitset(&current->real_blocked, 0);
-		recalc_sigpending();
-	}
-	spin_unlock_irq(&current->sighand->siglock);
+	ret = do_sigtimedwait(&s, &info, uts ? &t : NULL);
 
-	if (sig) {
-		ret = sig;
-		if (uinfo) {
-			if (copy_siginfo_to_user32(uinfo, &info))
-				ret = -EFAULT;
-		}
-	} else {
-		ret = timeout?-EINTR:-EAGAIN;
+	if (ret > 0 && uinfo) {
+		if (copy_siginfo_to_user32(uinfo, &info))
+			ret = -EFAULT;
 	}
+
 	return ret;
 
 }

kernel/signal.c

@@ -2503,6 +2503,66 @@ int copy_siginfo_to_user(siginfo_t __user *to, siginfo_t *from)
 
 #endif
 
+/**
+ *  do_sigtimedwait - wait for queued signals specified in @which
+ *  @which: queued signals to wait for
+ *  @info: if non-null, the signal's siginfo is returned here
+ *  @ts: upper bound on process time suspension
+ */
+int do_sigtimedwait(const sigset_t *which, siginfo_t *info,
+			const struct timespec *ts)
+{
+	struct task_struct *tsk = current;
+	long timeout = MAX_SCHEDULE_TIMEOUT;
+	sigset_t mask = *which;
+	int sig;
+
+	if (ts) {
+		if (!timespec_valid(ts))
+			return -EINVAL;
+		timeout = timespec_to_jiffies(ts);
+		/*
+		 * We can be close to the next tick, add another one
+		 * to ensure we will wait at least the time asked for.
+		 */
+		if (ts->tv_sec || ts->tv_nsec)
+			timeout++;
+	}
+
+	/*
+	 * Invert the set of allowed signals to get those we want to block.
+	 */
+	sigdelsetmask(&mask, sigmask(SIGKILL) | sigmask(SIGSTOP));
+	signotset(&mask);
+
+	spin_lock_irq(&tsk->sighand->siglock);
+	sig = dequeue_signal(tsk, &mask, info);
+	if (!sig && timeout) {
+		/*
+		 * None ready, temporarily unblock those we're interested
+		 * while we are sleeping in so that we'll be awakened when
+		 * they arrive.
+		 */
+		tsk->real_blocked = tsk->blocked;
+		sigandsets(&tsk->blocked, &tsk->blocked, &mask);
+		recalc_sigpending();
+		spin_unlock_irq(&tsk->sighand->siglock);
+
+		timeout = schedule_timeout_interruptible(timeout);
+
+		spin_lock_irq(&tsk->sighand->siglock);
+		sig = dequeue_signal(tsk, &mask, info);
+		tsk->blocked = tsk->real_blocked;
+		siginitset(&tsk->real_blocked, 0);
+		recalc_sigpending();
+	}
+	spin_unlock_irq(&tsk->sighand->siglock);
+
+	if (sig)
+		return sig;
+	return timeout ? -EINTR : -EAGAIN;
+}
+
 /**
  *  sys_rt_sigtimedwait - synchronously wait for queued signals specified
  *			in @uthese
@@ -2515,11 +2575,10 @@ SYSCALL_DEFINE4(rt_sigtimedwait, const sigset_t __user *, uthese,
 		siginfo_t __user *, uinfo, const struct timespec __user *, uts,
 		size_t, sigsetsize)
 {
-	int ret, sig;
 	sigset_t these;
 	struct timespec ts;
 	siginfo_t info;
-	long timeout;
+	int ret;
 
 	/* XXX: Don't preclude handling different sized sigset_t's.  */
 	if (sigsetsize != sizeof(sigset_t))
@@ -2528,55 +2587,16 @@ SYSCALL_DEFINE4(rt_sigtimedwait, const sigset_t __user *, uthese,
 	if (copy_from_user(&these, uthese, sizeof(these)))
 		return -EFAULT;
 
-	/*
-	 * Invert the set of allowed signals to get those we
-	 * want to block.
-	 */
-	sigdelsetmask(&these, sigmask(SIGKILL)|sigmask(SIGSTOP));
-	signotset(&these);
-
-	timeout = MAX_SCHEDULE_TIMEOUT;
 	if (uts) {
 		if (copy_from_user(&ts, uts, sizeof(ts)))
 			return -EFAULT;
-		if (!timespec_valid(&ts))
-			return -EINVAL;
-		timeout = timespec_to_jiffies(&ts) + (ts.tv_sec || ts.tv_nsec);
 	}
 
-	spin_lock_irq(&current->sighand->siglock);
-	sig = dequeue_signal(current, &these, &info);
-	if (!sig && timeout) {
-		/*
-		 * None ready -- temporarily unblock those we're
-		 * interested while we are sleeping in so that we'll
-		 * be awakened when they arrive.
-		 */
-		current->real_blocked = current->blocked;
-		sigandsets(&current->blocked, &current->blocked, &these);
-		recalc_sigpending();
-		spin_unlock_irq(&current->sighand->siglock);
-
-		timeout = schedule_timeout_interruptible(timeout);
-
-		spin_lock_irq(&current->sighand->siglock);
-		sig = dequeue_signal(current, &these, &info);
-		current->blocked = current->real_blocked;
-		siginitset(&current->real_blocked, 0);
-		recalc_sigpending();
-	}
-	spin_unlock_irq(&current->sighand->siglock);
+	ret = do_sigtimedwait(&these, &info, uts ? &ts : NULL);
 
-	if (sig) {
-		ret = sig;
-		if (uinfo) {
-			if (copy_siginfo_to_user(uinfo, &info))
-				ret = -EFAULT;
-		}
-	} else {
-		ret = -EAGAIN;
-		if (timeout)
-			ret = -EINTR;
+	if (ret > 0 && uinfo) {
+		if (copy_siginfo_to_user(uinfo, &info))
+			ret = -EFAULT;
 	}
 
 	return ret;