old-cross-binutils/gdb/testsuite/gdb.threads/fork-plus-threads.c

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PR threads/18600: Threads left stopped after fork+thread spawn When a program forks and another process start threads while gdb is handling the fork event, newly created threads are left stuck stopped by gdb, even though gdb presents them as "running", to the user. This can be seen with the test added by this patch. The test has the inferior fork a certain number of times and waits for all children to exit. Each fork child spawns a number of threads that do nothing and joins them immediately. Normally, the program should run unimpeded (from the point of view of the user) and exit very quickly. Without this fix, it doesn't because of some threads left stopped by gdb, so inferior 1 never exits. The program triggers when a new clone thread is found while inside the linux_stop_and_wait_all_lwps call in linux-thread-db.c: linux_stop_and_wait_all_lwps (); ALL_LWPS (lp) if (ptid_get_pid (lp->ptid) == pid) thread_from_lwp (lp->ptid); linux_unstop_all_lwps (); Within linux_stop_and_wait_all_lwps, we reach linux_handle_extended_wait with the "stopping" parameter set to 1, and because of that we don't mark the new lwp as resumed. As consequence, the subsequent resume_stopped_resumed_lwps, called from linux_unstop_all_lwps, never resumes the new LWP. There's lots of cruft in linux_handle_extended_wait that no longer makes sense. On systems with CLONE events support, we don't rely on libthread_db for thread listing anymore, so the code that preserves stop_requested and the handling of last_resume_kind is all dead. So the fix is to remove all that, and simply always mark the new LWP as resumed, so that resume_stopped_resumed_lwps re-resumes it. gdb/ChangeLog: 2015-07-30 Pedro Alves <palves@redhat.com> Simon Marchi <simon.marchi@ericsson.com> PR threads/18600 * linux-nat.c (linux_handle_extended_wait): On CLONE event, always mark the new thread as resumed. Remove STOPPING parameter. (wait_lwp): Adjust call to linux_handle_extended_wait. (linux_nat_filter_event): Adjust call to linux_handle_extended_wait. (resume_stopped_resumed_lwps): Add debug output. gdb/testsuite/ChangeLog: 2015-07-30 Simon Marchi <simon.marchi@ericsson.com> Pedro Alves <palves@redhat.com> PR threads/18600 * gdb.threads/fork-plus-threads.c: New file. * gdb.threads/fork-plus-threads.exp: New file.
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/* This testcase is part of GDB, the GNU debugger.
Copyright 2015-2016 Free Software Foundation, Inc.
PR threads/18600: Threads left stopped after fork+thread spawn When a program forks and another process start threads while gdb is handling the fork event, newly created threads are left stuck stopped by gdb, even though gdb presents them as "running", to the user. This can be seen with the test added by this patch. The test has the inferior fork a certain number of times and waits for all children to exit. Each fork child spawns a number of threads that do nothing and joins them immediately. Normally, the program should run unimpeded (from the point of view of the user) and exit very quickly. Without this fix, it doesn't because of some threads left stopped by gdb, so inferior 1 never exits. The program triggers when a new clone thread is found while inside the linux_stop_and_wait_all_lwps call in linux-thread-db.c: linux_stop_and_wait_all_lwps (); ALL_LWPS (lp) if (ptid_get_pid (lp->ptid) == pid) thread_from_lwp (lp->ptid); linux_unstop_all_lwps (); Within linux_stop_and_wait_all_lwps, we reach linux_handle_extended_wait with the "stopping" parameter set to 1, and because of that we don't mark the new lwp as resumed. As consequence, the subsequent resume_stopped_resumed_lwps, called from linux_unstop_all_lwps, never resumes the new LWP. There's lots of cruft in linux_handle_extended_wait that no longer makes sense. On systems with CLONE events support, we don't rely on libthread_db for thread listing anymore, so the code that preserves stop_requested and the handling of last_resume_kind is all dead. So the fix is to remove all that, and simply always mark the new LWP as resumed, so that resume_stopped_resumed_lwps re-resumes it. gdb/ChangeLog: 2015-07-30 Pedro Alves <palves@redhat.com> Simon Marchi <simon.marchi@ericsson.com> PR threads/18600 * linux-nat.c (linux_handle_extended_wait): On CLONE event, always mark the new thread as resumed. Remove STOPPING parameter. (wait_lwp): Adjust call to linux_handle_extended_wait. (linux_nat_filter_event): Adjust call to linux_handle_extended_wait. (resume_stopped_resumed_lwps): Add debug output. gdb/testsuite/ChangeLog: 2015-07-30 Simon Marchi <simon.marchi@ericsson.com> Pedro Alves <palves@redhat.com> PR threads/18600 * gdb.threads/fork-plus-threads.c: New file. * gdb.threads/fork-plus-threads.exp: New file.
2015-07-30 17:50:29 +00:00
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 <assert.h>
#include <pthread.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
/* Number of times the main process forks. */
#define NFORKS 10
/* Number of threads by each fork child. */
#define NTHREADS 10
static void *
thread_func (void *arg)
{
/* Empty. */
}
static void
fork_child (void)
{
pthread_t threads[NTHREADS];
int i;
int ret;
for (i = 0; i < NTHREADS; i++)
{
ret = pthread_create (&threads[i], NULL, thread_func, NULL);
assert (ret == 0);
}
for (i = 0; i < NTHREADS; i++)
{
ret = pthread_join (threads[i], NULL);
assert (ret == 0);
}
}
int
main (void)
{
pid_t childs[NFORKS];
int i;
int status;
int num_exited = 0;
/* Don't run forever if the wait loop below gets stuck. */
alarm (180);
for (i = 0; i < NFORKS; i++)
{
pid_t pid;
pid = fork ();
if (pid > 0)
{
/* Parent. */
childs[i] = pid;
}
else if (pid == 0)
{
/* Child. */
fork_child ();
return 0;
}
else
{
perror ("fork");
return 1;
}
}
while (num_exited != NFORKS)
{
pid_t pid = wait (&status);
if (pid == -1)
{
perror ("wait");
return 1;
}
if (WIFEXITED (status))
{
num_exited++;
}
else
{
printf ("Hmm, unexpected wait status 0x%x from child %d\n", status,
pid);
}
}
return 0;
}