[src/trunk]: src/sys/kern - lwp_need_userret(): only do it if ONPROC and !cur...

[ad <ad%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/13a8ab18896e
branches:  trunk
changeset: 461275:13a8ab18896e
user:      ad <ad%NetBSD.org@localhost>
date:      Thu Nov 21 18:17:36 2019 +0000

description:
- lwp_need_userret(): only do it if ONPROC and !curlwp, and explain why.
- Use signotify() in a couple more places.

diffstat:

 sys/kern/kern_lwp.c |  29 ++++++++++++++++++++---------
 sys/kern/kern_sig.c |  12 +++++++-----
 2 files changed, 27 insertions(+), 14 deletions(-)

diffs (112 lines):

diff -r 674dc383da17 -r 13a8ab18896e sys/kern/kern_lwp.c
--- a/sys/kern/kern_lwp.c       Thu Nov 21 17:57:40 2019 +0000
+++ b/sys/kern/kern_lwp.c       Thu Nov 21 18:17:36 2019 +0000
@@ -1,7 +1,7 @@
-/*     $NetBSD: kern_lwp.c,v 1.208 2019/11/14 16:23:52 maxv Exp $      */
+/*     $NetBSD: kern_lwp.c,v 1.209 2019/11/21 18:17:36 ad Exp $        */
 
 /*-
- * Copyright (c) 2001, 2006, 2007, 2008, 2009 The NetBSD Foundation, Inc.
+ * Copyright (c) 2001, 2006, 2007, 2008, 2009, 2019 The NetBSD Foundation, Inc.
  * All rights reserved.
  *
  * This code is derived from software contributed to The NetBSD Foundation
@@ -211,7 +211,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_lwp.c,v 1.208 2019/11/14 16:23:52 maxv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_lwp.c,v 1.209 2019/11/21 18:17:36 ad Exp $");
 
 #include "opt_ddb.h"
 #include "opt_lockdebug.h"
@@ -1147,7 +1147,7 @@
            firstsig(&p->p_sigpend.sp_set) != 0) {
                LIST_FOREACH(l2, &p->p_lwps, l_sibling) {
                        lwp_lock(l2);
-                       l2->l_flag |= LW_PENDSIG;
+                       signotify(l2);
                        lwp_unlock(l2);
                }
        }
@@ -1616,15 +1616,26 @@
 void
 lwp_need_userret(struct lwp *l)
 {
+
+       KASSERT(!cpu_intr_p());
        KASSERT(lwp_locked(l, NULL));
 
        /*
-        * Since the tests in lwp_userret() are done unlocked, make sure
-        * that the condition will be seen before forcing the LWP to enter
-        * kernel mode.
+        * If the LWP is in any state other than LSONPROC, we know that it
+        * is executing in-kernel and will hit userret() on the way out. 
+        *
+        * If the LWP is curlwp, then we know we'll be back out to userspace
+        * soon (can't be called from a hardware interrupt here).
+        *
+        * Otherwise, we can't be sure what the LWP is doing, so first make
+        * sure the update to l_flag will be globally visible, and then
+        * force the LWP to take a trip through trap() where it will do
+        * userret().
         */
-       membar_producer();
-       cpu_signotify(l);
+       if (l->l_stat == LSONPROC && l != curlwp) {
+               membar_producer();
+               cpu_signotify(l);
+       }
 }
 
 /*
diff -r 674dc383da17 -r 13a8ab18896e sys/kern/kern_sig.c
--- a/sys/kern/kern_sig.c       Thu Nov 21 17:57:40 2019 +0000
+++ b/sys/kern/kern_sig.c       Thu Nov 21 18:17:36 2019 +0000
@@ -1,7 +1,7 @@
-/*     $NetBSD: kern_sig.c,v 1.379 2019/11/20 19:37:53 pgoyette Exp $  */
+/*     $NetBSD: kern_sig.c,v 1.380 2019/11/21 18:17:36 ad Exp $        */
 
 /*-
- * Copyright (c) 2006, 2007, 2008 The NetBSD Foundation, Inc.
+ * Copyright (c) 2006, 2007, 2008, 2019 The NetBSD Foundation, Inc.
  * All rights reserved.
  *
  * This code is derived from software contributed to The NetBSD Foundation
@@ -70,7 +70,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_sig.c,v 1.379 2019/11/20 19:37:53 pgoyette Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_sig.c,v 1.380 2019/11/21 18:17:36 ad Exp $");
 
 #include "opt_ptrace.h"
 #include "opt_dtrace.h"
@@ -710,6 +710,9 @@
  *     current LWP.  May be called unlocked provided that LW_PENDSIG is set,
  *     and that the signal has been posted to the appopriate queue before
  *     LW_PENDSIG is set.
+ *
+ *     This should only ever be called with (l == curlwp), unless the
+ *     result does not matter (procfs, sysctl).
  */ 
 int
 sigispending(struct lwp *l, int signo)
@@ -1133,7 +1136,7 @@
         * Have the LWP check for signals.  This ensures that even if no LWP
         * is found to take the signal immediately, it should be taken soon.
         */
-       l->l_flag |= LW_PENDSIG;
+       signotify(l);
 
        /*
         * SIGCONT can be masked, but if LWP is stopped, it needs restart.
@@ -1167,7 +1170,6 @@
        switch (l->l_stat) {
        case LSRUN:
        case LSONPROC:
-               lwp_need_userret(l);
                rv = 1;
                break;