From 203dda8a636c46efa6d2b7587507c9a503668aaa Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Thu, 8 Oct 2020 22:34:34 +0000
Subject: [PATCH] sig_intr(9): return early if AST is not scheduled.

Check td_flags for relevant AST requests lock-less.  This opens the
race slightly wider where sig_intr() returns false negative, but might
be it is worth it.

Requested by:	mjg
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
---
 sys/kern/kern_sig.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index 8108d4cb3a5..ed4dd52b66d 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -3212,6 +3212,9 @@ sig_intr(void)
 	int ret;
 
 	td = curthread;
+	if ((td->td_flags & (TDF_NEEDSIGCHK | TDF_NEEDSUSPCHK)) == 0)
+		return (0);
+
 	p = td->td_proc;
 
 	PROC_LOCK(p);