[RFA] Fix internal error with 'set debug infrun 1' under high load

Philippe Waroquiers
2019-03-24T14:25:18Z

The test gdb.threads/watchthreads-reorder.exp verifies that the
'set debug infrun 1' debug output does not crash GDB.

Under high load, the test can still cause a GDB internal error (see details
below).

This patch checks that ptid differs from null_ptid to call
pid_to_str so that it does not crash.
The change also outputs event_ptid.

(top-gdb) bt
#0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
#1 0x00007f3d54a0642a in __GI_abort () at abort.c:89
#2 0x0000555c24c60e66 in dump_core () at ../../fixleaks/gdb/utils.c:201
#3 0x0000555c24c63d49 in internal_vproblem(internal_problem *, const char *, int, const char *, typedef __va_list_tag __va_list_tag *) (problem=problem@entry=0x555c25338d40 <internal_error_problem>, file=<optimized out>, line=287,
fmt=<optimized out>, ap=<optimized out>) at ../../fixleaks/gdb/utils.c:411
#4 0x0000555c24c63eab in internal_verror (file=<optimized out>, line=<optimized out>, fmt=<optimized out>,
ap=<optimized out>) at ../../fixleaks/gdb/utils.c:436
#5 0x0000555c249e8c22 in internal_error (file=file@entry=0x555c24e0f2ad "../../fixleaks/gdb/inferior.c",
line=line@entry=287, fmt=<optimized out>) at ../../fixleaks/gdb/common/errors.c:55
#6 0x0000555c247d3f5c in find_inferior_pid (pid=<optimized out>) at ../../fixleaks/gdb/inferior.c:287
#7 0x0000555c24ad2248 in find_inferior_pid (pid=<optimized out>) at ../../fixleaks/gdb/inferior.c:302
#8 find_inferior_ptid (ptid=...) at ../../fixleaks/gdb/inferior.c:301
#9 0x0000555c24c35f25 in find_thread_ptid (ptid=...) at ../../fixleaks/gdb/thread.c:522
#10 0x0000555c24b0ab4d in thread_db_target::pid_to_str[abi:cxx11](ptid_t) (
this=0x555c2532e3e0 <the_thread_db_target>, ptid=...) at ../../fixleaks/gdb/linux-thread-db.c:1637
#11 0x0000555c24c2f420 in target_pid_to_str[abi:cxx11](ptid_t) (ptid=...) at ../../fixleaks/gdb/target.c:2083
#12 0x0000555c24ad9cab in stop_all_threads () at ../../fixleaks/gdb/infrun.c:4373
#13 0x0000555c24ada00f in stop_waiting (ecs=<optimized out>) at ../../fixleaks/gdb/infrun.c:7464
#14 0x0000555c24adc401 in process_event_stop_test (ecs=ecs@entry=0x7ffc9402d9d0) at ../../fixleaks/gdb/infrun.c:6181
...
(top-gdb) fr 12
#12 0x0000555c24ad9cab in stop_all_threads () at ../../fixleaks/gdb/infrun.c:4373
(top-gdb) p event_ptid
$5 = {m_pid = 25419, m_lwp = 25427, m_tid = 0}
(top-gdb) p ptid
$6 = {m_pid = 0, m_lwp = 0, m_tid = 0}
(top-gdb) p ws
$7 = {kind = TARGET_WAITKIND_THREAD_EXITED, value = {integer = 0, sig = GDB_SIGNAL_0, related_pid = {m_pid = 0,
m_lwp = 0, m_tid = 0}, execd_pathname = 0x0, syscall_number = 0}}
(top-gdb)

The gdb.log corresponding to the above crash is:
(gdb) PASS: gdb.threads/watchthreads-reorder.exp: reorder1: set debug infrun 1
continue
Continuing.
infrun: clear_proceed_status_thread (Thread 0x7ffff7fcfb40 (LWP 25419))
infrun: clear_proceed_status_thread (Thread 0x7ffff7310700 (LWP 25427))
infrun: clear_proceed_status_thread (Thread 0x7ffff6b0f700 (LWP 25428))
infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)
infrun: proceed: resuming Thread 0x7ffff7fcfb40 (LWP 25419)
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [Thread 0x7ffff7fcfb40 (LWP 25419)] at 0x7ffff7344317
infrun: infrun_async(1)
infrun: prepare_to_wait
infrun: proceed: resuming Thread 0x7ffff7310700 (LWP 25427)
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [Thread 0x7ffff7310700 (LWP 25427)] at 0x5555555553d7
infrun: prepare_to_wait
infrun: proceed: resuming Thread 0x7ffff6b0f700 (LWP 25428)
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [Thread 0x7ffff6b0f700 (LWP 25428)] at 0x5555555554c8
infrun: prepare_to_wait
infrun: target_wait (-1.0.0, status) =
infrun: -1.0.0 [process -1],
infrun: status->kind = ignore
infrun: TARGET_WAITKIND_IGNORE
infrun: prepare_to_wait
Joining the threads.
[Thread 0x7ffff6b0f700 (LWP 25428) exited]
infrun: target_wait (-1.0.0, status) =
infrun: -1.0.0 [process -1],
infrun: status->kind = ignore
infrun: TARGET_WAITKIND_IGNORE
infrun: prepare_to_wait
infrun: target_wait (-1.0.0, status) =
infrun: 25419.25419.0 [Thread 0x7ffff7fcfb40 (LWP 25419)],
infrun: status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: TARGET_WAITKIND_STOPPED
infrun: stop_pc = 0x555555555e50
infrun: context switch
infrun: Switching context from Thread 0x7ffff6b0f700 (LWP 25428) to Thread 0x7ffff7fcfb40 (LWP 25419)
infrun: BPSTAT_WHAT_STOP_NOISY
infrun: stop_waiting
infrun: stop_all_threads
infrun: stop_all_threads, pass=0, iterations=0
infrun: Thread 0x7ffff7fcfb40 (LWP 25419) not executing
infrun: Thread 0x7ffff7310700 (LWP 25427) executing, need stop
[Thread 0x7ffff7310700 (LWP 25427) exited]
infrun: target_wait (-1.0.0, status) =
infrun: 25419.25427.0 [LWP 25427],
infrun: status->kind = thread exited, status = 0
infrun: infrun_async(0)
../../fixleaks/gdb/inferior.c:287: internal-error: inferior* find_inferior_pid(int): Assertion `pid != 0' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n) FAIL: gdb.threads/watchthreads-reorder.exp: reorder1: continue to breakpoint: break-at-exit (GDB internal error)
Resyncing due to internal error.
n
infrun: infrun_async(1)

This is a bug, please report it. For instructions, see:
<http://www.gnu.org/software/gdb/bugs/>.

infrun: infrun_async(0)
../../fixleaks/gdb/inferior.c:287: internal-error: inferior* find_inferior_pid(int): Assertion `pid != 0' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Create a core file of GDB? (y or n) y
---
gdb/infrun.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index ad7892105a..111879c318 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -4368,9 +4368,13 @@ stop_all_threads (void)
ptid_t ptid = ptid_t (ws.value.integer);

fprintf_unfiltered (gdb_stdlog,
- "infrun: %s exited while "
+ "infrun: %s "
+ "(event_ptid %s) exited while "
"stopping threads\n",
- target_pid_to_str (ptid).c_str ());
+ ptid == null_ptid
+ ? "<null thread>"
+ : target_pid_to_str (ptid).c_str (),
+ target_pid_to_str (event_ptid).c_str ());
}
}
else
--
2.20.1