signal: Use GROUP_STOP_PENDING to stop once for a single group stop
Currently task->signal->group_stop_count is used to decide whether to
stop for group stop. However, if there is a task in the group which
is taking a long time to stop, other tasks which are continued by
ptrace would repeatedly stop for the same group stop until the group
stop is complete.
Conversely, if a ptraced task is in TASK_TRACED state, the debugger
won't get notified of group stops which is inconsistent compared to
the ptraced task in any other state.
This patch introduces GROUP_STOP_PENDING which tracks whether a task
is yet to stop for the group stop in progress. The flag is set when a
group stop starts and cleared when the task stops the first time for
the group stop, and consulted whenever whether the task should
participate in a group stop needs to be determined. Note that now
tasks in TASK_TRACED also participate in group stop.
This results in the following behavior changes.
* For a single group stop, a ptracer would see at most one stop
reported.
* A ptracee in TASK_TRACED now also participates in group stop and the
tracer would get the notification. However, as a ptraced task could
be in TASK_STOPPED state or any ptrace trap could consume group
stop, the notification may still be missing. These will be
addressed with further patches.
* A ptracee may start a group stop while one is still in progress if
the tracer let it continue with stop signal delivery. Group stop
code handles this correctly.
Oleg:
* Spotted that a task might skip signal check even when its
GROUP_STOP_PENDING is set. Fixed by updating
recalc_sigpending_tsk() to check GROUP_STOP_PENDING instead of
group_stop_count.
* Pointed out that task->group_stop should be cleared whenever
task->signal->group_stop_count is cleared. Fixed accordingly.
* Pointed out the behavior inconsistency between TASK_TRACED and
RUNNING and the last behavior change.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 85f5104..b2a17df 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1775,8 +1775,11 @@
/*
* task->group_stop flags
*/
+#define GROUP_STOP_PENDING (1 << 16) /* task should stop for group stop */
#define GROUP_STOP_CONSUME (1 << 17) /* consume group stop count */
+extern void task_clear_group_stop_pending(struct task_struct *task);
+
#ifdef CONFIG_PREEMPT_RCU
#define RCU_READ_UNLOCK_BLOCKED (1 << 0) /* blocked while in RCU read-side. */