Add a knob to not drop signal with default ignored or ignored actions

(cherry picked from commit bc38762474caed2d41d2562e28f56aa211f47ceb)

3 files changed, 40 insertions, 27 deletions

diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index 1cab25aa5a40..4f6f424fb05d 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -163,6 +163,12 @@ SYSCTL_BOOL(_kern, OID_AUTO, sigfastblock_fetch_always, CTLFLAG_RWTUN,
     "Fetch sigfastblock word on each syscall entry for proper "
     "blocking semantic");
 
+static bool	kern_sig_discard_ign = true;
+SYSCTL_BOOL(_kern, OID_AUTO, sig_discard_ign, CTLFLAG_RWTUN,
+    &kern_sig_discard_ign, 0,
+    "Discard ignored signals on delivery, otherwise queue them to "
+    "the target queue");
+
 SYSINIT(signal, SI_SUB_P1003_1B, SI_ORDER_FIRST+3, sigqueue_start, NULL);
 
 /*
@@ -1290,6 +1296,9 @@ kern_sigtimedwait(struct thread *td, sigset_t waitset, ksiginfo_t *ksi,
 	PROC_LOCK(p);
 	saved_mask = td->td_sigmask;
 	SIGSETNAND(td->td_sigmask, waitset);
+	if ((p->p_sysent->sv_flags & SV_SIG_DISCIGN) != 0 ||
+	    !kern_sig_discard_ign)
+		td->td_pflags2 |= TDP2_SIGWAIT;
 	for (;;) {
 		mtx_lock(&ps->ps_mtx);
 		sig = cursig(td);
@@ -1352,6 +1361,7 @@ kern_sigtimedwait(struct thread *td, sigset_t waitset, ksiginfo_t *ksi,
 		if (error == 0 && (p->p_ptevents & PTRACE_SYSCALL) != 0)
 			traced = true;
 	}
+	td->td_pflags2 &= ~TDP2_SIGWAIT;
 
 	new_block = saved_mask;
 	SIGSETNAND(new_block, td->td_sigmask);
@@ -2200,22 +2210,25 @@ tdsendsignal(struct proc *p, struct thread *td, int sig, ksiginfo_t *ksi)
 	SDT_PROBE3(proc, , , signal__send, td, p, sig);
 
 	/*
-	 * If the signal is being ignored,
-	 * then we forget about it immediately.
-	 * (Note: we don't set SIGCONT in ps_sigignore,
-	 * and if it is set to SIG_IGN,
-	 * action will be SIG_DFL here.)
+	 * If the signal is being ignored, then we forget about it
+	 * immediately, except when the target process executes
+	 * sigwait().  (Note: we don't set SIGCONT in ps_sigignore,
+	 * and if it is set to SIG_IGN, action will be SIG_DFL here.)
 	 */
 	mtx_lock(&ps->ps_mtx);
 	if (SIGISMEMBER(ps->ps_sigignore, sig)) {
-		SDT_PROBE3(proc, , , signal__discard, td, p, sig);
+		if (kern_sig_discard_ign &&
+		    (p->p_sysent->sv_flags & SV_SIG_DISCIGN) == 0) {
+			SDT_PROBE3(proc, , , signal__discard, td, p, sig);
 
-		mtx_unlock(&ps->ps_mtx);
-		if (ksi && (ksi->ksi_flags & KSI_INS))
-			ksiginfo_tryfree(ksi);
-		return (ret);
-	}
-	if (SIGISMEMBER(td->td_sigmask, sig))
+			mtx_unlock(&ps->ps_mtx);
+			if (ksi && (ksi->ksi_flags & KSI_INS))
+				ksiginfo_tryfree(ksi);
+			return (ret);
+		} else {
+			action = SIG_CATCH;
+		}
+	} else if (SIGISMEMBER(td->td_sigmask, sig))
 		action = SIG_HOLD;
 	else if (SIGISMEMBER(ps->ps_sigcatch, sig))
 		action = SIG_CATCH;
@@ -2950,11 +2963,13 @@ issignal(struct thread *td)
 		}
 
 		/*
-		 * We should see pending but ignored signals
-		 * only if P_TRACED was on when they were posted.
+		 * We should allow pending but ignored signals below
+		 * only if there is sigwait() active, or P_TRACED was
+		 * on when they were posted.
 		 */
 		if (SIGISMEMBER(ps->ps_sigignore, sig) &&
-		    (p->p_flag & P_TRACED) == 0) {
+		    (p->p_flag & P_TRACED) == 0 &&
+		    (td->td_pflags2 & TDP2_SIGWAIT) == 0) {
 			sigqueue_delete(&td->td_sigqueue, sig);
 			sigqueue_delete(&p->p_sigqueue, sig);
 			continue;
@@ -3066,10 +3081,11 @@ issignal(struct thread *td)
 				PROC_SUNLOCK(p);
 				mtx_lock(&ps->ps_mtx);
 				goto next;
-			} else if (prop & SIGPROP_IGNORE) {
+			} else if ((prop & SIGPROP_IGNORE) != 0 &&
+			    (td->td_pflags2 & TDP2_SIGWAIT) == 0) {
 				/*
-				 * Except for SIGCONT, shouldn't get here.
-				 * Default action is to ignore; drop it.
+				 * Default action is to ignore; drop it if
+				 * not in kern_sigtimedwait().
 				 */
 				break;		/* == ignore */
 			} else
@@ -3077,15 +3093,10 @@ issignal(struct thread *td)
 			/*NOTREACHED*/
 
 		case (intptr_t)SIG_IGN:
-			/*
-			 * Masking above should prevent us ever trying
-			 * to take action on an ignored signal other
-			 * than SIGCONT, unless process is traced.
-			 */
-			if ((prop & SIGPROP_CONT) == 0 &&
-			    (p->p_flag & P_TRACED) == 0)
-				printf("issignal\n");
-			break;		/* == ignore */
+			if ((td->td_pflags2 & TDP2_SIGWAIT) == 0)
+				break;		/* == ignore */
+			else
+				return (sig);
 
 		default:
 			/*
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index d4476ac8d410..373e62bd266d 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -529,6 +529,7 @@ do {									\
 #define	TDP2_SBPAGES	0x00000001 /* Owns sbusy on some pages */
 #define	TDP2_COMPAT32RB	0x00000002 /* compat32 ABI for robust lists */
 #define	TDP2_ACCT	0x00000004 /* Doing accounting */
+#define	TDP2_SIGWAIT	0x00000008 /* Ignore ignored signals */
 
 /*
  * Reasons that the current thread can not be run yet.
diff --git a/sys/sys/sysent.h b/sys/sys/sysent.h
index c2cbd77a92b9..95e9dcb1a335 100644
--- a/sys/sys/sysent.h
+++ b/sys/sys/sysent.h
@@ -161,6 +161,7 @@ struct sysentvec {
 #define	SV_TIMEKEEP	0x040000	/* Shared page timehands. */
 #define	SV_ASLR		0x080000	/* ASLR allowed. */
 #define	SV_RNG_SEED_VER	0x100000	/* random(4) reseed generation. */
+#define	SV_SIG_DISCIGN	0x200000	/* Do not discard ignored signals */
 
 #define	SV_ABI_MASK	0xff
 #define	SV_PROC_FLAG(p, x)	((p)->p_sysent->sv_flags & (x))