[patch] Fix internal-error on dead LWPs with no associated thread

[Jan Kratochvil <jan dot kratochvil at redhat dot com>]

Hi,

original bugreport:
https://bugzilla.redhat.com/show_bug.cgi?id=471819

linux-nat.c:1662: internal-error: linux_nat_resume: Assertion `lp != NULL' failed.

A reproducing testcase included.
No regressions on {x86_64,i686}-fedora-linux-gnu.


Thanks,
Jan


gdb/
2009-06-27  Jan Kratochvil  <jan.kratochvil@redhat.com>

	Fix internal error on dead LWPs with no associated thread.
	* linux-nat.c (num_lwps): Do not count DEAD LWPs.
	(delete_lwp): Only set LP as DEAD if it is INFERIOR_PTID.
	(iterate_over_lwps): Skip DEAD LPs.  Discard DEAD LPs not in
	INFERIOR_PTID.
	(linux_nat_resume): Do not resume DEAD LPs.  Extend the debug message.
	* linux-nat.h (struct lwp_info): New field `dead'.

gdb/testsuite/
2009-06-27  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.threads/current-lwp-dead.exp, gdb.threads/current-lwp-dead.c: New.

--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -941,7 +941,7 @@ num_lwps (int pid)
   struct lwp_info *lp;
 
   for (lp = lwp_list; lp; lp = lp->next)
-    if (ptid_get_pid (lp->ptid) == pid)
+    if (ptid_get_pid (lp->ptid) == pid && !lp->dead)
       count++;
 
   return count;
@@ -991,6 +991,13 @@ delete_lwp (ptid_t ptid)
   if (!lp)
     return;
 
+  if (ptid_equal (ptid, inferior_ptid))
+    {
+      /* Delay the deletion the same way as in delete_thread_1.  */
+      lp->dead = 1;
+      return;
+    }
+
   if (lpprev)
     lpprev->next = lp->next;
   else
@@ -1063,6 +1070,15 @@ iterate_over_lwps (ptid_t filter,
     {
       lpnext = lp->next;
 
+      /* Ignored already dead LWPs.  Moreover delete them if we no longer have
+	 to keep them around.  */
+      if (lp->dead)
+      	{
+	  if (!ptid_equal (lp->ptid, inferior_ptid))
+	    delete_lwp (lp->ptid);
+	  continue;
+	}
+
       if (ptid_match (lp->ptid, filter))
 	{
 	  if ((*callback) (lp, data))
@@ -1732,15 +1748,19 @@ linux_nat_resume (struct target_ops *ops,
   /* Convert to something the lower layer understands.  */
   ptid = pid_to_ptid (GET_LWP (lp->ptid));
 
-  linux_ops->to_resume (linux_ops, ptid, step, signo);
-  memset (&lp->siginfo, 0, sizeof (lp->siginfo));
+  if (!lp->dead)
+    {
+      linux_ops->to_resume (linux_ops, ptid, step, signo);
+      memset (&lp->siginfo, 0, sizeof (lp->siginfo));
+    }
 
   if (debug_linux_nat)
     fprintf_unfiltered (gdb_stdlog,
-			"LLR: %s %s, %s (resume event thread)\n",
+			"LLR: %s %s, %s, %s (resume event thread)\n",
 			step ? "PTRACE_SINGLESTEP" : "PTRACE_CONT",
 			target_pid_to_str (ptid),
-			signo ? strsignal (signo) : "0");
+			signo ? strsignal (signo) : "0",
+			lp->dead ? "dead" : "alive");
 
   restore_child_signals_mask (&prev_mask);
   if (target_can_async_p ())
--- a/gdb/linux-nat.h
+++ b/gdb/linux-nat.h
@@ -32,6 +32,12 @@ struct lwp_info
      and overall process id.  */
   ptid_t ptid;
 
+  /* If this flag is set, the lwp is known to be dead already (exit
+     event already received in a my_waitpid()).  Such LWP should not longer be
+     iterated and it is being kept only temporarily if it is still referenced
+     by INFERIOR_PTID.  */
+  int dead;
+
   /* Non-zero if this LWP is cloned.  In this context "cloned" means
      that the LWP is reporting to its parent using a signal other than
      SIGCHLD.  */
new file mode 100644
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/current-lwp-dead.c
@@ -0,0 +1,75 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2009 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+   Do not use threads as we need to exploit a bug in LWP code masked by the
+   threads code otherwise.
+
+   INFERIOR_PTID must point to exited LWP.  Here we use the initial LWP as it
+   is automatically INFERIOR_PTID for GDB.
+
+   Finally we need to call target_resume (RESUME_ALL, ...) which we invoke by
+   NEW_THREAD_EVENT (called from the new LWP as initial LWP is exited now).  */
+
+#define _GNU_SOURCE
+#include <sched.h>
+#include <assert.h>
+#include <unistd.h>
+#include <stdlib.h>
+
+#define STACK_SIZE 0x1000
+
+static int
+fn_abort (void *unused)
+{
+  return 0;	/* at-fn_abort */
+}
+
+static int
+fn (void *unused)
+{
+  int i;
+  unsigned char *stack;
+  int new_pid;
+
+  i = sleep (1);
+  assert (i == 0);
+
+  stack = malloc (STACK_SIZE);
+  assert (stack != NULL);
+
+  new_pid = clone (fn_abort, stack + STACK_SIZE, CLONE_FILES | CLONE_VM, NULL,
+		   NULL, NULL, NULL);
+  assert (new_pid > 0);
+
+  return 0;
+}
+
+int
+main (int argc, char **argv)
+{
+  unsigned char *stack;
+  int new_pid;
+
+  stack = malloc (STACK_SIZE);
+  assert (stack != NULL);
+
+  new_pid = clone (fn, stack + STACK_SIZE, CLONE_FILES | CLONE_VM, NULL, NULL,
+		   NULL, NULL);
+  assert (new_pid > 0);
+
+  return 0;
+}
new file mode 100644
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/current-lwp-dead.exp
@@ -0,0 +1,31 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2009 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Please email any bugs, comments, and/or additions to this file to:
+# bug-gdb@gnu.org
+
+if { [prepare_for_testing current-lwp-dead.exp current-lwp-dead] } {
+    return -1
+}
+
+if {[runto_main] <= 0} {
+    untested current-lwp-dead.exp
+    return -1
+}
+
+gdb_breakpoint "fn_abort"
+gdb_continue_to_breakpoint "fn_abort" ".*at-fn_abort.*"