* [Bug threads/18600] After forking and threads spawning, gdb leaves newly created threads stopped
2015-06-25 17:08 [Bug threads/18600] New: After forking and threads spawning, gdb leaves newly created threads stopped simon.marchi at ericsson dot com
@ 2015-06-25 17:08 ` simon.marchi at ericsson dot com
2015-07-07 22:11 ` simon.marchi at ericsson dot com
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From: simon.marchi at ericsson dot com @ 2015-06-25 17:08 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=18600
Simon Marchi <simon.marchi at ericsson dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |marc.khouzam at ericsson dot com
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2015-06-25 17:08 [Bug threads/18600] New: After forking and threads spawning, gdb leaves newly created threads stopped simon.marchi at ericsson dot com
2015-06-25 17:08 ` [Bug threads/18600] " simon.marchi at ericsson dot com
@ 2015-07-07 22:11 ` simon.marchi at ericsson dot com
2015-07-30 17:55 ` cvs-commit at gcc dot gnu.org
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From: simon.marchi at ericsson dot com @ 2015-07-07 22:11 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=18600
--- Comment #1 from Simon Marchi <simon.marchi at ericsson dot com> ---
Relevant discussion thread:
https://sourceware.org/ml/gdb-patches/2015-07/msg00153.html
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2015-06-25 17:08 [Bug threads/18600] New: After forking and threads spawning, gdb leaves newly created threads stopped simon.marchi at ericsson dot com
2015-06-25 17:08 ` [Bug threads/18600] " simon.marchi at ericsson dot com
2015-07-07 22:11 ` simon.marchi at ericsson dot com
@ 2015-07-30 17:55 ` cvs-commit at gcc dot gnu.org
2015-07-30 17:55 ` cvs-commit at gcc dot gnu.org
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From: cvs-commit at gcc dot gnu.org @ 2015-07-30 17:55 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=18600
--- Comment #3 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Pedro Alves <palves@sourceware.org>:
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=69dde7dcb81f6baf2b823dcc03e040c29ee5de7d
commit 69dde7dcb81f6baf2b823dcc03e040c29ee5de7d
Author: Pedro Alves <palves@redhat.com>
Date: Wed Jul 22 18:01:46 2015 +0100
PR threads/18600: Inferiors left around after fork+thread spawn
The new gdb.threads/fork-plus-threads.exp test exposes one more
problem. When one types "info inferiors" after running the program,
one see's a couple inferior left still, while there should only be
inferior #1 left. E.g.:
(gdb) info inferiors
Num Description Executable
4 process 8393 /home/pedro/bugs/src/test
2 process 8388 /home/pedro/bugs/src/test
* 1 <null> /home/pedro/bugs/src/test
(gdb) info threads
Calling prune_inferiors() manually at this point (from a top gdb) does
not remove them, because they still have inf->pid != 0 (while they
shouldn't). This suggests that we never mourned those inferiors.
Enabling logs (master + previous patch) we see:
...
WL: waitpid Thread 0x7ffff7fc2740 (LWP 9513) received Trace/breakpoint
trap (stopped)
WL: Handling extended status 0x03057f
LHEW: Got clone event from LWP 9513, new child is LWP 9579
[New Thread 0x7ffff37b8700 (LWP 9579)]
WL: waitpid Thread 0x7ffff7fc2740 (LWP 9508) received 0 (exited)
WL: Thread 0x7ffff7fc2740 (LWP 9508) exited.
^^^^^^^^
[Thread 0x7ffff7fc2740 (LWP 9508) exited]
WL: waitpid Thread 0x7ffff7fc2740 (LWP 9499) received 0 (exited)
WL: Thread 0x7ffff7fc2740 (LWP 9499) exited.
[Thread 0x7ffff7fc2740 (LWP 9499) exited]
RSRL: resuming stopped-resumed LWP Thread 0x7ffff37b8700 (LWP 9579) at
0x3615ef4ce1: step=0
...
(gdb) info inferiors
Num Description Executable
5 process 9508 /home/pedro/bugs/src/test
^^^^
4 process 9503 /home/pedro/bugs/src/test
3 process 9500 /home/pedro/bugs/src/test
2 process 9499 /home/pedro/bugs/src/test
* 1 <null> /home/pedro/bugs/src/test
(gdb)
...
Note the "Thread 0x7ffff7fc2740 (LWP 9508) exited." line.
That's this in wait_lwp:
/* Check if the thread has exited. */
if (WIFEXITED (status) || WIFSIGNALED (status))
{
thread_dead = 1;
if (debug_linux_nat)
fprintf_unfiltered (gdb_stdlog, "WL: %s exited.\n",
target_pid_to_str (lp->ptid));
}
}
That was the leader thread reporting an exit, meaning the whole
process is gone. So the problem is that this code doesn't understand
that an WIFEXITED status of the leader LWP should be reported to
infrun as process exit.
gdb/ChangeLog:
2015-07-30 Pedro Alves <palves@redhat.com>
PR threads/18600
* linux-nat.c (wait_lwp): Report to the core when thread group
leader exits.
gdb/testsuite/ChangeLog:
2015-07-30 Pedro Alves <palves@redhat.com>
PR threads/18600
* gdb.threads/fork-plus-threads.exp: Test that "info inferiors"
only shows inferior 1.
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2015-06-25 17:08 [Bug threads/18600] New: After forking and threads spawning, gdb leaves newly created threads stopped simon.marchi at ericsson dot com
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2015-07-30 17:55 ` cvs-commit at gcc dot gnu.org
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2015-07-30 18:05 ` cvs-commit at gcc dot gnu.org
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From: cvs-commit at gcc dot gnu.org @ 2015-07-30 17:55 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=18600
--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Pedro Alves <palves@sourceware.org>:
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=4dd63d488a76482543517c4c4cde699ee6fa33ef
commit 4dd63d488a76482543517c4c4cde699ee6fa33ef
Author: Pedro Alves <palves@redhat.com>
Date: Thu Jul 30 18:50:29 2015 +0100
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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2015-07-30 17:55 ` cvs-commit at gcc dot gnu.org
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2015-07-30 18:05 ` cvs-commit at gcc dot gnu.org
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From: cvs-commit at gcc dot gnu.org @ 2015-07-30 18:05 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=18600
--- Comment #4 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The gdb-7.10-branch branch has been updated by Pedro Alves
<palves@sourceware.org>:
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=b31f5e79aac67f61a684c3af281caebd2ac1eece
commit b31f5e79aac67f61a684c3af281caebd2ac1eece
Author: Pedro Alves <palves@redhat.com>
Date: Thu Jul 30 18:55:36 2015 +0100
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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` (4 preceding siblings ...)
2015-07-30 18:05 ` cvs-commit at gcc dot gnu.org
@ 2015-07-30 18:05 ` cvs-commit at gcc dot gnu.org
2015-07-30 18:26 ` palves at redhat dot com
` (2 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2015-07-30 18:05 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=18600
--- Comment #5 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The gdb-7.10-branch branch has been updated by Pedro Alves
<palves@sourceware.org>:
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=7476be08b73fdfba4eb91d891b235d4cf2e70f3b
commit 7476be08b73fdfba4eb91d891b235d4cf2e70f3b
Author: Pedro Alves <palves@redhat.com>
Date: Thu Jul 30 18:55:36 2015 +0100
PR threads/18600: Inferiors left around after fork+thread spawn
The new gdb.threads/fork-plus-threads.exp test exposes one more
problem. When one types "info inferiors" after running the program,
one see's a couple inferior left still, while there should only be
inferior #1 left. E.g.:
(gdb) info inferiors
Num Description Executable
4 process 8393 /home/pedro/bugs/src/test
2 process 8388 /home/pedro/bugs/src/test
* 1 <null> /home/pedro/bugs/src/test
(gdb) info threads
Calling prune_inferiors() manually at this point (from a top gdb) does
not remove them, because they still have inf->pid != 0 (while they
shouldn't). This suggests that we never mourned those inferiors.
Enabling logs (master + previous patch) we see:
...
WL: waitpid Thread 0x7ffff7fc2740 (LWP 9513) received Trace/breakpoint
trap (stopped)
WL: Handling extended status 0x03057f
LHEW: Got clone event from LWP 9513, new child is LWP 9579
[New Thread 0x7ffff37b8700 (LWP 9579)]
WL: waitpid Thread 0x7ffff7fc2740 (LWP 9508) received 0 (exited)
WL: Thread 0x7ffff7fc2740 (LWP 9508) exited.
^^^^^^^^
[Thread 0x7ffff7fc2740 (LWP 9508) exited]
WL: waitpid Thread 0x7ffff7fc2740 (LWP 9499) received 0 (exited)
WL: Thread 0x7ffff7fc2740 (LWP 9499) exited.
[Thread 0x7ffff7fc2740 (LWP 9499) exited]
RSRL: resuming stopped-resumed LWP Thread 0x7ffff37b8700 (LWP 9579) at
0x3615ef4ce1: step=0
...
(gdb) info inferiors
Num Description Executable
5 process 9508 /home/pedro/bugs/src/test
^^^^
4 process 9503 /home/pedro/bugs/src/test
3 process 9500 /home/pedro/bugs/src/test
2 process 9499 /home/pedro/bugs/src/test
* 1 <null> /home/pedro/bugs/src/test
(gdb)
...
Note the "Thread 0x7ffff7fc2740 (LWP 9508) exited." line.
That's this in wait_lwp:
/* Check if the thread has exited. */
if (WIFEXITED (status) || WIFSIGNALED (status))
{
thread_dead = 1;
if (debug_linux_nat)
fprintf_unfiltered (gdb_stdlog, "WL: %s exited.\n",
target_pid_to_str (lp->ptid));
}
}
That was the leader thread reporting an exit, meaning the whole
process is gone. So the problem is that this code doesn't understand
that an WIFEXITED status of the leader LWP should be reported to
infrun as process exit.
gdb/ChangeLog:
2015-07-30 Pedro Alves <palves@redhat.com>
PR threads/18600
* linux-nat.c (wait_lwp): Report to the core when thread group
leader exits.
gdb/testsuite/ChangeLog:
2015-07-30 Pedro Alves <palves@redhat.com>
PR threads/18600
* gdb.threads/fork-plus-threads.exp: Test that "info inferiors"
only shows inferior 1.
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2015-06-25 17:08 [Bug threads/18600] New: After forking and threads spawning, gdb leaves newly created threads stopped simon.marchi at ericsson dot com
` (5 preceding siblings ...)
2015-07-30 18:05 ` cvs-commit at gcc dot gnu.org
@ 2015-07-30 18:26 ` palves at redhat dot com
2015-08-06 14:02 ` cvs-commit at gcc dot gnu.org
2015-08-06 14:03 ` cvs-commit at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: palves at redhat dot com @ 2015-07-30 18:26 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=18600
Pedro Alves <palves at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
CC| |palves at redhat dot com
Resolution|--- |FIXED
--- Comment #6 from Pedro Alves <palves at redhat dot com> ---
Fixed.
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` (6 preceding siblings ...)
2015-07-30 18:26 ` palves at redhat dot com
@ 2015-08-06 14:02 ` cvs-commit at gcc dot gnu.org
2015-08-06 14:03 ` cvs-commit at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2015-08-06 14:02 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=18600
--- Comment #7 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Pedro Alves <palves@sourceware.org>:
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=f0ce0d3a331129309a46a6a9ac85fce35acae72b
commit f0ce0d3a331129309a46a6a9ac85fce35acae72b
Author: Pedro Alves <palves@redhat.com>
Date: Thu Jul 23 16:01:01 2015 +0100
gdbserver: move_out_of_jump_pad_callback misses switching current thread
While hacking on the fix for PR threads/18600 (Threads left stopped
after fork+thread spawn), I once saw its test (fork-plus-threads.exp)
FAIL against gdbserver because move_out_of_jump_pad_callback has a
gdb_breakpoint_here call, and the caller isn't making sure the current
thread points to the right thread. In the case I saw, the current
thread pointed to the wrong process, so gdb_breakpoint_here returned
the wrong answer. Unfortunately I didn't save logs. Still, seems
obvious enough and it should fix a potential occasional racy FAIL.
Tested on x86_64 Fedora 20.
gdb/gdbserver/ChangeLog:
2015-08-06 Pedro Alves <palves@redhat.com>
* linux-low.c (move_out_of_jump_pad_callback): Temporarily switch
the current thread.
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2015-08-06 14:02 ` cvs-commit at gcc dot gnu.org
@ 2015-08-06 14:03 ` cvs-commit at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2015-08-06 14:03 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=18600
--- Comment #8 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The gdb-7.10-branch branch has been updated by Pedro Alves
<palves@sourceware.org>:
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=a01c46276aa3a16c2ac1dae249df14e39d1c281f
commit a01c46276aa3a16c2ac1dae249df14e39d1c281f
Author: Pedro Alves <palves@redhat.com>
Date: Thu Aug 6 15:02:26 2015 +0100
gdbserver: move_out_of_jump_pad_callback misses switching current thread
While hacking on the fix for PR threads/18600 (Threads left stopped
after fork+thread spawn), I once saw its test (fork-plus-threads.exp)
FAIL against gdbserver because move_out_of_jump_pad_callback has a
gdb_breakpoint_here call, and the caller isn't making sure the current
thread points to the right thread. In the case I saw, the current
thread pointed to the wrong process, so gdb_breakpoint_here returned
the wrong answer. Unfortunately I didn't save logs. Still, seems
obvious enough and it should fix a potential occasional racy FAIL.
Tested on x86_64 Fedora 20.
gdb/gdbserver/ChangeLog:
2015-08-06 Pedro Alves <palves@redhat.com>
* linux-low.c (move_out_of_jump_pad_callback): Temporarily switch
the current thread.
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