[review v2] infrun: handle already-exited threads when attempting to stop

Tankut Baris Aktemur (Code Review)
2019-11-04T10:23:48Z

infrun: handle already-exited threads when attempting to stop

In stop_all_threads, GDB sends signals to other threads in an attempt
to stop them. While in a typical scenario the expected wait status is
TARGET_WAITKIND_STOPPED, it is possible that the thread GDB attempted
to stop has already terminated. If so, a waitstatus other than
TARGET_WAITKIND_STOPPED would be received. Handle this case
appropriately.

If a wait status that denotes thread termination is ignored, GDB goes
into an infinite loop in stop_all_threads.
E.g.:

~~~
$ gdb ./a.out
(gdb) start
...
(gdb) add-inferior -exec ./a.out
...
(gdb) inferior 2
...
(gdb) start
...
(gdb) set schedule-multiple on
(gdb) set debug infrun 2
(gdb) continue
Continuing.
infrun: clear_proceed_status_thread (process 23419)
infrun: clear_proceed_status_thread (process 23703)
infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)
infrun: proceed: resuming process 23419
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 23419] at 0x55555555514e
infrun: infrun_async(1)
infrun: prepare_to_wait
infrun: proceed: resuming process 23703
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 23703] at 0x55555555514e
infrun: prepare_to_wait
infrun: target_wait (-1.0.0, status) =
infrun: 23703.23703.0 [process 23703],
infrun: status->kind = exited, status = 0
infrun: handle_inferior_event status->kind = exited, status = 0
[Inferior 2 (process 23703) exited normally]
infrun: stop_waiting
infrun: stop_all_threads
infrun: stop_all_threads, pass=0, iterations=0
infrun: process 23419 executing, need stop
infrun: target_wait (-1.0.0, status) =
infrun: 23419.23419.0 [process 23419],
infrun: status->kind = exited, status = 0
infrun: stop_all_threads status->kind = exited, status = 0 process 23419
infrun: process 23419 executing, already stopping
infrun: target_wait (-1.0.0, status) =
infrun: -1.0.0 [process -1],
infrun: status->kind = no-resumed
infrun: stop_all_threads status->kind = no-resumed process -1
infrun: process 23419 executing, already stopping
infrun: target_wait (-1.0.0, status) =
infrun: -1.0.0 [process -1],
infrun: status->kind = no-resumed
infrun: stop_all_threads status->kind = no-resumed process -1
infrun: process 23419 executing, already stopping
infrun: target_wait (-1.0.0, status) =
infrun: -1.0.0 [process -1],
infrun: status->kind = no-resumed
infrun: stop_all_threads status->kind = no-resumed process -1
infrun: process 23419 executing, already stopping
infrun: target_wait (-1.0.0, status) =
infrun: -1.0.0 [process -1],
infrun: status->kind = no-resumed
infrun: stop_all_threads status->kind = no-resumed process -1
infrun: process 23419 executing, already stopping
~~~

And this polling goes on forever. This patch prevents the infinite
looping behavior. For the same scenario above, we obtain the
following behavior:

~~~
...
(gdb) continue
Continuing.
infrun: clear_proceed_status_thread (process 1635)
infrun: clear_proceed_status_thread (process 1763)
infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)
infrun: proceed: resuming process 1635
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 1635] at 0x55555555514e
infrun: infrun_async(1)
infrun: prepare_to_wait
infrun: proceed: resuming process 1763
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 1763] at 0x55555555514e
infrun: prepare_to_wait
infrun: target_wait (-1.0.0, status) =
infrun: 1635.1635.0 [process 1635],
infrun: status->kind = exited, status = 0
infrun: handle_inferior_event status->kind = exited, status = 0
[Inferior 1 (process 1635) exited normally]
infrun: stop_waiting
infrun: stop_all_threads
infrun: stop_all_threads, pass=0, iterations=0
infrun: process 1763 executing, need stop
infrun: target_wait (-1.0.0, status) =
infrun: 1763.1763.0 [process 1763],
infrun: status->kind = exited, status = 0
infrun: stop_all_threads status->kind = exited, status = 0 process 1763
[Inferior 2 (process 1763) exited normally]
infrun: stop_all_threads, pass=1, iterations=1
infrun: stop_all_threads done
(gdb) info inferiors
Num Description Executable
* 1 <null> /path/to/a.out
2 <null> /path/to/a.out
(gdb) info threads
No threads.
(gdb)
~~~

gdb/ChangeLog:
2019-11-04 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>

* infrun.c (stop_all_threads): Do NOT ignore
TARGET_WAITKIND_NO_RESUMED, TARGET_WAITKIND_THREAD_EXITED,
TARGET_WAITKIND_EXITED, TARGET_WAITKIND_SIGNALLED wait statuses
received from threads we attempt to stop.

Change-Id: I7cec98f40283773b79255d998511da434e9cd408
---
M gdb/infrun.c
1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index f628fd1..45aa1d9 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -4489,8 +4489,35 @@
|| ws.kind == TARGET_WAITKIND_EXITED
|| ws.kind == TARGET_WAITKIND_SIGNALLED)
{
- /* All resumed threads exited
- or one thread/process exited/signalled. */
+ if (event_ptid != minus_one_ptid)
+ {
+ thread_info *t = find_thread_ptid (event_ptid);
+ if (t == nullptr)
+ {
+ /* This is the first time we see this thread. */
+ t = add_thread (event_ptid);
+ }
+
+ /* Set the threads as non-executing to avoid infinitely
+ waiting for them to stop. */
+ mark_non_executing_threads (event_ptid, ws);
+
+ if (ws.kind == TARGET_WAITKIND_NO_RESUMED)
+ {
+ /* Do nothing. Already marked the threads. */
+ }
+ if (ws.kind == TARGET_WAITKIND_THREAD_EXITED)
+ delete_thread (t);
+ else
+ {
+ /* TARGET_WAITKIND_EXITED or
+ TARGET_WAITKIND_SIGNALLED. */
+ /* Need to restore the context because
+ handle_inferior_exit switches it. */
+ scoped_restore_current_pspace_and_thread restore;
+ handle_inferior_exit (event_ptid, ws);
+ }
+ }
}
else
{

--
Gerrit-Project: binutils-gdb
Gerrit-Branch: master
Gerrit-Change-Id: I7cec98f40283773b79255d998511da434e9cd408
Gerrit-Change-Number: 133
Gerrit-PatchSet: 2
Gerrit-Owner: Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
Gerrit-Reviewer: Luis Machado <luis.machado@linaro.org>
Gerrit-Reviewer: Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
Gerrit-MessageType: newpatchset