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[patch] Workaround for 10970, 12702, avoid calling waitpid
- From: dje at google dot com (Doug Evans)
- To: gdb-patches at sourceware dot org, jan dot kratochvil at redhat dot com
- Date: Tue, 17 May 2011 11:19:20 -0700 (PDT)
- Subject: [patch] Workaround for 10970, 12702, avoid calling waitpid
Hi.
A proper fix seems much more invasive, and this works well enough
for a large number of cases.
I'll be checking it in tomorrow if there are no objections.
The testcase handles 10970.
I'm not sure how to write a regression test for 12702 without
employing something like what I wrote in 12702 to show the bug,
or running gdb under gdb in order to effect the necessary
sequencing of events. Testing for 10970 (main does pthread_exit)
at least exercises the issue if not all the ways it can happen.
2011-05-17 Jan Kratochvil <jan.kratochvil@redhat.com>
Doug Evans <dje@google.com>
Workaround for bugs 10970, 12702.
* linux-nat.c (linux_lwp_is_zombie): New function.
(wait_lwp): Try to avoid calling waitpid on thread group leader
if it will hang.
testsuite/
* gdb.threads/leader-exit.c: New file.
* gdb.threads/leader-exit.exp: New file.
Index: linux-nat.c
===================================================================
RCS file: /cvs/src/src/gdb/linux-nat.c,v
retrieving revision 1.204
diff -u -p -r1.204 linux-nat.c
--- linux-nat.c 13 May 2011 17:28:19 -0000 1.204
+++ linux-nat.c 17 May 2011 18:04:06 -0000
@@ -2356,6 +2356,33 @@ linux_handle_extended_wait (struct lwp_i
_("unknown ptrace event %d"), event);
}
+/* Return non-zero if LWP is a zombie. */
+
+static int
+linux_lwp_is_zombie (long lwp)
+{
+ char buffer[MAXPATHLEN];
+ FILE *procfile;
+ int retval = 0;
+
+ sprintf (buffer, "/proc/%ld/status", lwp);
+ procfile = fopen (buffer, "r");
+ if (procfile == NULL)
+ {
+ warning (_("unable to open /proc file '%s'"), buffer);
+ return 0;
+ }
+ while (fgets (buffer, sizeof (buffer), procfile) != NULL)
+ if (strcmp (buffer, "State:\tZ (zombie)\n") == 0)
+ {
+ retval = 1;
+ break;
+ }
+ fclose (procfile);
+
+ return retval;
+}
+
/* Wait for LP to stop. Returns the wait status, or 0 if the LWP has
exited. */
@@ -2363,16 +2390,44 @@ static int
wait_lwp (struct lwp_info *lp)
{
pid_t pid;
- int status;
+ int status = 0;
int thread_dead = 0;
gdb_assert (!lp->stopped);
gdb_assert (lp->status == 0);
- pid = my_waitpid (GET_LWP (lp->ptid), &status, 0);
- if (pid == -1 && errno == ECHILD)
+ /* Bugs 10970, 12702.
+ Thread group leader may have exited in which case we'll lock up in
+ waitpid if there are other threads, even if they are all zombies too.
+ Basically, we're not supposed to use waitpid this way.
+ We can call waitpid with WNOHANG and obviously avoid the lock up, but we
+ don't want that here.
+ __WCLONE is not applicable for the leader so we can't use that.
+ LINUX_NAT_THREAD_ALIVE cannot be used here as it requires a STOPPED
+ process; it gets ESRCH both for the zombie and for running processes.
+
+ As a workaround, check if we're waiting for the thread group leader and
+ if it's a zombie, and avoid calling waitpid if it is.
+ This is racy, what if the tgl becomes a zombie right after we check?
+ But it seems to work in many cases, at least until a better fix/rewrite
+ can be done. */
+
+ if (is_lwp (lp->ptid)
+ && GET_PID (lp->ptid) == GET_LWP (lp->ptid)
+ && linux_lwp_is_zombie (GET_LWP (lp->ptid)))
+ {
+ thread_dead = 1;
+ if (debug_linux_nat)
+ fprintf_unfiltered (gdb_stdlog,
+ "WL: Thread group leader %s vanished.\n",
+ target_pid_to_str (lp->ptid));
+ }
+
+ if (!thread_dead)
{
- pid = my_waitpid (GET_LWP (lp->ptid), &status, __WCLONE);
+ pid = my_waitpid (GET_LWP (lp->ptid), &status, 0);
+ if (pid == -1 && errno == ECHILD)
+ pid = my_waitpid (GET_LWP (lp->ptid), &status, __WCLONE);
if (pid == -1 && errno == ECHILD)
{
/* The thread has previously exited. We need to delete it
Index: testsuite/gdb.threads/leader-exit.c
===================================================================
RCS file: testsuite/gdb.threads/leader-exit.c
diff -N testsuite/gdb.threads/leader-exit.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.threads/leader-exit.c 17 May 2011 18:04:06 -0000
@@ -0,0 +1,43 @@
+/* Clean exit of the thread group leader should not break GDB.
+
+ Copyright 2007, 2011 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/>. */
+
+#include <pthread.h>
+#include <assert.h>
+#include <unistd.h>
+
+static void *
+start (void *arg)
+{
+ for (;;)
+ pause ();
+ /* NOTREACHED */
+ return arg;
+}
+
+int
+main (void)
+{
+ pthread_t thread;
+ int i;
+
+ i = pthread_create (&thread, NULL, start, NULL); /* create1 */
+ assert (i == 0);
+
+ pthread_exit (NULL);
+ /* NOTREACHED */
+ return 0;
+}
Index: testsuite/gdb.threads/leader-exit.exp
===================================================================
RCS file: testsuite/gdb.threads/leader-exit.exp
diff -N testsuite/gdb.threads/leader-exit.exp
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.threads/leader-exit.exp 17 May 2011 18:04:06 -0000
@@ -0,0 +1,71 @@
+# Copyright (C) 2007, 2011 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/>.
+
+# Exit of the thread group leader should not break GDB.
+
+# This file was written by Jan Kratochvil <jan.kratochvil@redhat.com>.
+
+if $tracelevel then {
+ strace $tracelevel
+}
+
+set testfile "leader-exit"
+set srcfile ${testfile}.c
+set binfile ${objdir}/${subdir}/${testfile}
+
+if {[gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug}] != "" } {
+ return -1
+}
+
+gdb_exit
+gdb_start
+gdb_reinitialize_dir $srcdir/$subdir
+gdb_load ${binfile}
+runto_main
+
+# For this to work we must be sure to consume the "Continuing."
+# message first, or GDB's signal handler may not be in place.
+# We also want to ensure the thread is running.
+send_gdb "continue\n"
+gdb_expect {
+ -re "Continuing.\[\r\n\]+.*New Thread" {
+ pass "continue"
+ }
+ timeout {
+ fail "continue (timeout)"
+ }
+}
+
+proc stop_process { description } {
+ global gdb_prompt
+
+ after 1000 {send_gdb "\003"}
+ gdb_expect {
+ -re "Program received signal SIGINT.*$gdb_prompt $"
+ {
+ pass $description
+ }
+ timeout
+ {
+ fail "$description (timeout)"
+ }
+ }
+}
+
+stop_process "Threads could be stopped"
+
+gdb_test "info threads" \
+ "\\* 2 *Thread \[^\r\n\]* in \[^\r\n\]*" \
+ "Single thread has been left"