Module Name: src
Committed By: kamil
Date: Tue Jun 4 11:54:04 UTC 2019
Modified Files:
src/sys/kern: kern_lwp.c kern_sig.c
Log Message:
Stop trying to inform debugger about events from an exiting child
Do not emit signals to parent for if a process is demising:
- fork/vfork/similar
- lwp created/exited
- exec
- syscall entry/exit
With these changes Go applications can be traced without a clash under
a debugger, at least without deadlocking always. The culprit reason was
an attempt to inform a debugger in the middle of exit1() call about
a dying LWP. Go applications perform exit(2) without collecting threads
first. Verified with GDB and picotrace-based utilities like sigtracer.
PR kern/53120
PR port-arm/51677
PR bin/54060
PR bin/49662
PR kern/52548
To generate a diff of this commit:
cvs rdiff -u -r1.201 -r1.202 src/sys/kern/kern_lwp.c
cvs rdiff -u -r1.358 -r1.359 src/sys/kern/kern_sig.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/kern_lwp.c
diff -u src/sys/kern/kern_lwp.c:1.201 src/sys/kern/kern_lwp.c:1.202
--- src/sys/kern/kern_lwp.c:1.201 Fri May 17 03:34:26 2019
+++ src/sys/kern/kern_lwp.c Tue Jun 4 11:54:03 2019
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_lwp.c,v 1.201 2019/05/17 03:34:26 ozaki-r Exp $ */
+/* $NetBSD: kern_lwp.c,v 1.202 2019/06/04 11:54:03 kamil Exp $ */
/*-
* Copyright (c) 2001, 2006, 2007, 2008, 2009 The NetBSD Foundation, Inc.
@@ -211,7 +211,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_lwp.c,v 1.201 2019/05/17 03:34:26 ozaki-r Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_lwp.c,v 1.202 2019/06/04 11:54:03 kamil Exp $");
#include "opt_ddb.h"
#include "opt_lockdebug.h"
@@ -1084,9 +1084,17 @@ lwp_exit(struct lwp *l)
if ((p->p_slflag & (PSL_TRACED|PSL_TRACELWP_EXIT)) ==
(PSL_TRACED|PSL_TRACELWP_EXIT)) {
mutex_enter(p->p_lock);
- p->p_lwp_exited = l->l_lid;
- eventswitch(TRAP_LWP);
- mutex_enter(proc_lock);
+ if (ISSET(p->p_sflag, PS_WEXIT)) {
+ mutex_exit(p->p_lock);
+ /*
+ * We are exiting, bail out without informing parent
+ * about a terminating LWP as it would deadlock.
+ */
+ } else {
+ p->p_lwp_exited = l->l_lid;
+ eventswitch(TRAP_LWP);
+ mutex_enter(proc_lock);
+ }
}
LIST_REMOVE(l, l_list);
Index: src/sys/kern/kern_sig.c
diff -u src/sys/kern/kern_sig.c:1.358 src/sys/kern/kern_sig.c:1.359
--- src/sys/kern/kern_sig.c:1.358 Mon May 6 08:05:03 2019
+++ src/sys/kern/kern_sig.c Tue Jun 4 11:54:03 2019
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_sig.c,v 1.358 2019/05/06 08:05:03 kamil Exp $ */
+/* $NetBSD: kern_sig.c,v 1.359 2019/06/04 11:54:03 kamil Exp $ */
/*-
* Copyright (c) 2006, 2007, 2008 The NetBSD Foundation, Inc.
@@ -70,7 +70,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_sig.c,v 1.358 2019/05/06 08:05:03 kamil Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_sig.c,v 1.359 2019/06/04 11:54:03 kamil Exp $");
#include "opt_ptrace.h"
#include "opt_dtrace.h"
@@ -913,6 +913,19 @@ trapsignal(struct lwp *l, ksiginfo_t *ks
mutex_enter(proc_lock);
mutex_enter(p->p_lock);
+ /*
+ * If we are exiting, demise now.
+ *
+ * This avoids notifying tracer and deadlocking.
+ */
+ if (__predict_false(ISSET(p->p_sflag, PS_WEXIT))) {
+ mutex_exit(p->p_lock);
+ mutex_exit(proc_lock);
+ lwp_exit(l);
+ panic("trapsignal");
+ /* NOTREACHED */
+ }
+
mask = &l->l_sigmask;
ps = p->p_sigacts;
action = SIGACTION_PS(ps, signo).sa_handler;
@@ -1569,6 +1582,19 @@ eventswitch(int code)
(code == TRAP_EXEC));
/*
+ * If we are exiting, demise now.
+ *
+ * This avoids notifying tracer and deadlocking.
+ */
+ if (__predict_false(ISSET(p->p_sflag, PS_WEXIT))) {
+ mutex_exit(p->p_lock);
+ mutex_exit(proc_lock);
+ lwp_exit(l);
+ panic("eventswitch");
+ /* NOTREACHED */
+ }
+
+ /*
* If there's a pending SIGKILL process it immediately.
*/
if (p->p_xsig == SIGKILL ||
@@ -1622,6 +1648,21 @@ sigswitch(int ppmask, int signo, bool re
KASSERT(p->p_nrlwps > 0);
/*
+ * If we are exiting, demise now.
+ *
+ * This avoids notifying tracer and deadlocking.
+ */
+ if (__predict_false(ISSET(p->p_sflag, PS_WEXIT))) {
+ mutex_exit(p->p_lock);
+ if (relock) {
+ mutex_exit(proc_lock);
+ }
+ lwp_exit(l);
+ panic("sigswitch");
+ /* NOTREACHED */
+ }
+
+ /*
* On entry we know that the process needs to stop. If it's
* the result of a 'sideways' stop signal that has been sourced
* through issignal(), then stop other LWPs in the process too.
@@ -2395,6 +2436,18 @@ proc_stoptrace(int trapno, int sysnum, c
mutex_enter(p->p_lock);
/*
+ * If we are exiting, demise now.
+ *
+ * This avoids notifying tracer and deadlocking.
+ */
+ if (__predict_false(ISSET(p->p_sflag, PS_WEXIT))) {
+ mutex_exit(p->p_lock);
+ lwp_exit(l);
+ panic("proc_stoptrace");
+ /* NOTREACHED */
+ }
+
+ /*
* If there's a pending SIGKILL process it immediately.
*/
if (p->p_xsig == SIGKILL ||
