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gdbserver/Linux: unbreak thread event randomization 

Wanting to make sure the new continue-pending-status.exp test tests
both cases of threads 2 and 3 reporting an event, I added counters to
the test, to make it FAIL if events for both threads aren't seen.
Assuming a well behaved backend, and given a reasonable number of
iterations, it should PASS.

However, running that against GNU/Linux gdbserver, I found that
surprisingly, that FAILed.  GDBserver always reported the breakpoint
hit for the same thread.

Turns out that I broke gdbserver's thread event randomization
recently, with git commit 582511be ([gdbserver] linux-low.c: better
starvation avoidance, handle non-stop mode too).  In that commit I
missed that the thread structure also has a status_pending_p field...
The end result was that count_events_callback always returns 0, and
then if no thread is stepping, select_event_lwp always returns the
event thread.  IOW, no randomization is happening at all.  Quite
curious how all the other changes in that patch were sufficient to fix
non-stop-fair-events.exp anyway even with that broken.

Tested on x86_64 Fedora 20, native and gdbserver.

gdb/gdbserver/ChangeLog:
2015-03-19 Pedro Alves  <palves@redhat.com>

	* linux-low.c (count_events_callback, select_event_lwp_callback):
	Use the lwp's status_pending_p field, not the thread's.

gdb/testsuite/ChangeLog:
2015-03-19  Pedro Alves  <palves@redhat.com>

	* gdb.threads/continue-pending-status.exp (saw_thread_2)
	(saw_thread_3): New globals.
	(top level): Increment them when an event for the corresponding
	thread is seen.
	(no thread starvation): New test.
This commit is contained in:
Pedro Alves 2015-03-15 19:35:26 +00:00
parent eb54c8bf08
commit 8bf3b159e5
6 changed files with 38 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
gdb/ChangeLog
View File

@ -1,3 +1,8 @@
2015-03-19 Pedro Alves <palves@redhat.com>
* linux-low.c (count_events_callback, select_event_lwp_callback):
Use the lwp's status_pending_p field, not the thread's.
2015-03-19 Pedro Alves <palves@redhat.com>
* linux-nat.c (status_callback): Return early if the LWP has no

5
gdb/gdbserver/ChangeLog
View File

@ -1,3 +1,8 @@
2015-03-19 Pedro Alves <palves@redhat.com>
* linux-low.c (count_events_callback, select_event_lwp_callback):
Use the lwp's status_pending_p field, not the thread's.
2015-03-19 Pedro Alves <palves@redhat.com>
* linux-low.c (select_event_lwp_callback): Update comments to

7
gdb/gdbserver/linux-low.c
View File

@ -2238,6 +2238,7 @@ static int
count_events_callback (struct inferior_list_entry *entry, void *data)
{
struct thread_info *thread = (struct thread_info *) entry;
struct lwp_info *lp = get_thread_lwp (thread);
int *count = data;
gdb_assert (count != NULL);
@ -2245,7 +2246,7 @@ count_events_callback (struct inferior_list_entry *entry, void *data)
/* Count only resumed LWPs that have an event pending. */
if (thread->last_status.kind == TARGET_WAITKIND_IGNORE
&& thread->last_resume_kind != resume_stop
&& thread->status_pending_p)
&& lp->status_pending_p)
(*count)++;
return 0;
@ -2273,6 +2274,7 @@ static int
select_event_lwp_callback (struct inferior_list_entry *entry, void *data)
{
struct thread_info *thread = (struct thread_info *) entry;
struct lwp_info *lp = get_thread_lwp (thread);
int *selector = data;
gdb_assert (selector != NULL);
@ -2280,7 +2282,7 @@ select_event_lwp_callback (struct inferior_list_entry *entry, void *data)
/* Select only resumed LWPs that have an event pending. */
if (thread->last_resume_kind != resume_stop
&& thread->last_status.kind == TARGET_WAITKIND_IGNORE
&& thread->status_pending_p)
&& lp->status_pending_p)
if ((*selector)-- == 0)
return 1;
@ -2324,6 +2326,7 @@ select_event_lwp (struct lwp_info **orig_lp)
/* First see how many events we have. */
find_inferior (&all_threads, count_events_callback, &num_events);
gdb_assert (num_events > 0);
/* Now randomly pick a LWP out of those that have had
events. */

1
gdb/linux-nat.c
View File

@ -2841,6 +2841,7 @@ select_event_lwp (ptid_t filter, struct lwp_info **orig_lp, int *status)
/* First see how many events we have. */
iterate_over_lwps (filter, count_events_callback, &num_events);
gdb_assert (num_events > 0);
/* Now randomly pick a LWP out of those that have had
events. */

8
gdb/testsuite/ChangeLog
View File

@ -1,3 +1,11 @@
2015-03-19 Pedro Alves <palves@redhat.com>
* gdb.threads/continue-pending-status.exp (saw_thread_2)
(saw_thread_3): New globals.
(top level): Increment them when an event for the corresponding
thread is seen.
(no thread starvation): New test.
2015-03-19 Pedro Alves <palves@redhat.com>
* gdb.threads/continue-pending-status.c: New file.

14
gdb/testsuite/gdb.threads/continue-pending-status.exp
View File

@ -56,6 +56,13 @@ proc get_current_thread {} {
set attempts 20
# These track whether we saw events for both threads 2 and 3. If the
# backend always returns the breakpoint hit for the same thread, then
# it fails to make sure threads aren't starved, and we'll fail the
# assert after the loop.
set saw_thread_2 0
set saw_thread_3 0
for {set i 0} {$i < $attempts} {incr i} {
with_test_prefix "attempt $i" {
gdb_test "b $srcfile:$break_line" \
@ -71,8 +78,10 @@ for {set i 0} {$i < $attempts} {incr i} {
# the resume and go straight to consuming the pending event.
set thread [get_current_thread]
if {$thread == 2} {
incr saw_thread_2
set thread 3
} else {
incr saw_thread_3
set thread 2
}
gdb_test "thread $thread" \
@ -108,3 +117,8 @@ for {set i 0} {$i < $attempts} {incr i} {
}
}
}
verbose -log "saw_thread_2=$saw_thread_2"
verbose -log "saw_thread_3=$saw_thread_3"
gdb_assert {$saw_thread_2 > 0 && $saw_thread_3 > 0} "no thread starvation"