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Fix lwp_suspend/unsuspend imbalance in linux_wait_1

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This patch fixes imbalanced lwp_suspend/unsuspend calls caused by the
premature choosing of another event for fairness.

select_event_lwp would switch the event before a call to
unsuspend_all_lwps, thus it would be called with the wrong event.

This caused an assertion failure: unsuspend LWP xx, suspended=-1 when
testing  gdb.threads/non-stop-fair-events.exp with ARM range stepping in
GDBServer.

This patch moves the switch of event after the unsuspend/unstop calls.

No regressions, tested on ubuntu 14.04 ARMv7 and x86.
With gdbserver-native.

gdb/gdbserver/ChangeLog:

	* linux-low.c (linux_wait_1): Move event switch after unsuspend_lwps.
This commit is contained in:
Antoine Tremblay
2016-08-31 13:46:22 -04:00
parent f99bd5f2c1
commit 3aa5cfa0d1
2 changed files with 23 additions and 18 deletions
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4
gdb/gdbserver/ChangeLog
View File

@ -1,3 +1,7 @@
2016-08-31 Antoine Tremblay <antoine.tremblay@ericsson.com>
* linux-low.c (linux_wait_1): Move event switch after unsuspend_lwps.
2016-08-25 Adhemerval Zanella <adhemerval.zanella@linaro.org>
PR server/20491

37
gdb/gdbserver/linux-low.c
View File

@ -3771,24 +3771,6 @@ linux_wait_1 (ptid_t ptid,
if (!non_stop)
stop_all_lwps (0, NULL);
/* If we're not waiting for a specific LWP, choose an event LWP
from among those that have had events. Giving equal priority
to all LWPs that have had events helps prevent
starvation. */
if (ptid_equal (ptid, minus_one_ptid))
{
event_child->status_pending_p = 1;
event_child->status_pending = w;
select_event_lwp (&event_child);
/* current_thread and event_child must stay in sync. */
current_thread = get_lwp_thread (event_child);
event_child->status_pending_p = 0;
w = event_child->status_pending;
}
if (step_over_finished)
{
if (!non_stop)
@ -3813,6 +3795,25 @@ linux_wait_1 (ptid_t ptid,
}
}
/* If we're not waiting for a specific LWP, choose an event LWP
from among those that have had events. Giving equal priority
to all LWPs that have had events helps prevent
starvation. */
if (ptid_equal (ptid, minus_one_ptid))
{
event_child->status_pending_p = 1;
event_child->status_pending = w;
select_event_lwp (&event_child);
/* current_thread and event_child must stay in sync. */
current_thread = get_lwp_thread (event_child);
event_child->status_pending_p = 0;
w = event_child->status_pending;
}
/* Stabilize threads (move out of jump pads). */
if (!non_stop)
stabilize_threads ();