posix-timers: Target group sigqueue to current task only if not exiting

A sigqueue belonging to a posix timer, which target is not a specific thread but a whole thread group, is preferrably targeted to the current task if it is part of that thread group. However nothing prevents a posix timer event from queueing such a sigqueue from a reaped yet running task. The interruptible code space between exit_notify() and the final call to schedule() is enough for posix_timer_fn() hrtimer to fire. If that happens while the current task is part of the thread group target, it is proposed to handle it but since its sighand pointer may have been cleared already, the sigqueue is dropped even if there are other tasks running within the group that could handle it. As a result posix timers with thread group wide target may miss signals when some of their threads are exiting. Fix this with verifying that the current task hasn't been through exit_notify() before proposing it as a preferred target so as to ensure that its sighand is still here and stable. complete_signal() might still reconsider the choice and find a better target within the group if current has passed retarget_shared_pending() already.

Frederic Weisbecker committed 1 year ago

Commit 63dffec1 parent 4d17c251 file · +4 −3Browse files

Unified · Split

kernel/signal.c+4−3

@@ -1959,14 +1959,15 @@ static void posixtimer_queue_sigqueue(struct sigqueue q, struct task_struct t, · 1958 unmodified lines
1959	1959	*
1960	1960	* Where type is not PIDTYPE_PID, signals must be delivered to the
1961	1961	* process. In this case, prefer to deliver to current if it is in
1962		− * the same thread group as the target process, which avoids
1963		− * unnecessarily waking up a potentially idle task.
	1962	+ * the same thread group as the target process and its sighand is
	1963	+ * stable, which avoids unnecessarily waking up a potentially idle task.
1964	1964	*/
1965	1965	static inline struct task_struct posixtimer_get_target(struct k_itimer tmr)
1966	1966	{
1967	1967	struct task_struct *t = pid_task(tmr->it_pid, tmr->it_pid_type);
1968	1968
1969		− if (t && tmr->it_pid_type != PIDTYPE_PID && same_thread_group(t, current))
	1969	+ if (t && tmr->it_pid_type != PIDTYPE_PID &&
	1970	+ same_thread_group(t, current) && !current->exit_state)
1970	1971	t = current;
1971	1972	return t;
1972	1973	}