In r198506, kern_sigsuspend() started doing cursig/postsig loop to make

sure that a signal was delivered to the thread before returning from
syscall. Signal delivery puts new return frame on the user stack, and
modifies trap frame to enter signal handler. As a consequence, syscall
return code sets EINTR as error return for signal frame, instead of the
syscall return.

Also, for ia64, due to different registers layout for those two kind of
frames, usermode sigsegfaulted when returned from signal handler.

Use newly-introduced cpu_set_syscall_retval(9) to set syscall result,
and return EJUSTRETURN from kern_sigsuspend() to prevent syscall return
code from modifying this frame [1].

Another issue is that pending SIGCONT might be cancelled by SIGSTOP,
causing postsig() not to deliver any catched signal [2]. Modify
postsig() to return 1 if signal was posted, and 0 otherwise, and use
this in the kern_sigsuspend loop.

Proposed by:	marcel [1]
Noted by:	davidxu [2]
Reviewed by:	marcel, davidxu
MFC after:	1 month

2 files changed, 8 insertions, 9 deletions

diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index e174df1..412e00d 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -1471,21 +1471,19 @@ kern_sigsuspend(struct thread *td, sigset_t mask)
 	 * thread. But sigsuspend should return only on signal
 	 * delivery.
 	 */
+	cpu_set_syscall_retval(td, EINTR);
 	for (has_sig = 0; !has_sig;) {
 		while (msleep(&p->p_sigacts, &p->p_mtx, PPAUSE|PCATCH, "pause",
 			0) == 0)
 			/* void */;
 		thread_suspend_check(0);
 		mtx_lock(&p->p_sigacts->ps_mtx);
-		while ((sig = cursig(td, SIG_STOP_ALLOWED)) != 0) {
-			postsig(sig);
-			has_sig = 1;
-		}
+		while ((sig = cursig(td, SIG_STOP_ALLOWED)) != 0)
+			has_sig += postsig(sig);
 		mtx_unlock(&p->p_sigacts->ps_mtx);
 	}
 	PROC_UNLOCK(p);
-	/* always return EINTR rather than ERESTART... */
-	return (EINTR);
+	return (EJUSTRETURN);
 }
 
 #ifdef COMPAT_43	/* XXX - COMPAT_FBSD3 */
@@ -2670,7 +2668,7 @@ thread_stopped(struct proc *p)
  * Take the action for the specified signal
  * from the current set of pending signals.
  */
-void
+int
 postsig(sig)
 	register int sig;
 {
@@ -2689,7 +2687,7 @@ postsig(sig)
 	ksiginfo_init(&ksi);
 	if (sigqueue_get(&td->td_sigqueue, sig, &ksi) == 0 &&
 	    sigqueue_get(&p->p_sigqueue, sig, &ksi) == 0)
-		return;
+		return (0);
 	ksi.ksi_signo = sig;
 	if (ksi.ksi_code == SI_TIMER)
 		itimer_accept(p, ksi.ksi_timerid, &ksi);
@@ -2757,6 +2755,7 @@ postsig(sig)
 		}
 		(*p->p_sysent->sv_sendsig)(action, &ksi, &returnmask);
 	}
+	return (1);
 }
 
 /*
diff --git a/sys/sys/signalvar.h b/sys/sys/signalvar.h
index c27a128..65d9cf5 100644
--- a/sys/sys/signalvar.h
+++ b/sys/sys/signalvar.h
@@ -330,7 +330,7 @@ void	gsignal(int pgid, int sig);
 void	killproc(struct proc *p, char *why);
 void	pgsigio(struct sigio **, int signum, int checkctty);
 void	pgsignal(struct pgrp *pgrp, int sig, int checkctty);
-void	postsig(int sig);
+int	postsig(int sig);
 void	psignal(struct proc *p, int sig);
 int	psignal_event(struct proc *p, struct sigevent *, ksiginfo_t *);
 struct sigacts *sigacts_alloc(void);