signal: Refactor send_sigqueue()

To handle posix timers which have their signal ignored via SIG_IGN properly
it is required to requeue a ignored signal for delivery when SIG_IGN is
lifted so the timer gets rearmed.

Split the required code out of send_sigqueue() so it can be reused in
context of sigaction().

While at it rename send_sigqueue() to posixtimer_send_sigqueue() so its
clear what this is about.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/20241105064213.586453412@linutronix.de

4 files changed, 47 insertions, 39 deletions

diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index 947176582de9..52611ea923b2 100644
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -109,6 +109,7 @@ static inline void posix_cputimers_rt_watchdog(struct posix_cputimers *pct,
 
 void posixtimer_rearm_itimer(struct task_struct *p);
 bool posixtimer_init_sigqueue(struct sigqueue *q);
+int posixtimer_send_sigqueue(struct k_itimer *tmr);
 bool posixtimer_deliver_signal(struct kernel_siginfo *info);
 void posixtimer_free_timer(struct k_itimer *timer);
 
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index bd9f569231d9..36283c1c55e9 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -340,7 +340,6 @@ extern int send_sig(int, struct task_struct *, int);
 extern int zap_other_threads(struct task_struct *p);
 extern struct sigqueue *sigqueue_alloc(void);
 extern void sigqueue_free(struct sigqueue *);
-extern int send_sigqueue(struct sigqueue *, struct pid *, enum pid_type, int si_private);
 extern int do_sigaction(int, struct k_sigaction *, struct k_sigaction *);
 
 static inline void clear_notify_signal(void)
diff --git a/kernel/signal.c b/kernel/signal.c
index 911ed3ab479e..5b71e26abb0e 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1947,40 +1947,54 @@ void sigqueue_free(struct sigqueue *q)
 		__sigqueue_free(q);
 }
 
-int send_sigqueue(struct sigqueue *q, struct pid *pid, enum pid_type type, int si_private)
+static void posixtimer_queue_sigqueue(struct sigqueue *q, struct task_struct *t, enum pid_type type)
 {
-	int sig = q->info.si_signo;
 	struct sigpending *pending;
+	int sig = q->info.si_signo;
+
+	signalfd_notify(t, sig);
+	pending = (type != PIDTYPE_PID) ? &t->signal->shared_pending : &t->pending;
+	list_add_tail(&q->list, &pending->list);
+	sigaddset(&pending->signal, sig);
+	complete_signal(sig, t, type);
+}
+
+/*
+ * This function is used by POSIX timers to deliver a timer signal.
+ * Where type is PIDTYPE_PID (such as for timers with SIGEV_THREAD_ID
+ * set), the signal must be delivered to the specific thread (queues
+ * into t->pending).
+ *
+ * Where type is not PIDTYPE_PID, signals must be delivered to the
+ * process. In this case, prefer to deliver to current if it is in
+ * the same thread group as the target process, which avoids
+ * unnecessarily waking up a potentially idle task.
+ */
+static inline struct task_struct *posixtimer_get_target(struct k_itimer *tmr)
+{
+	struct task_struct *t = pid_task(tmr->it_pid, tmr->it_pid_type);
+
+	if (t && tmr->it_pid_type != PIDTYPE_PID && same_thread_group(t, current))
+		t = current;
+	return t;
+}
+
+int posixtimer_send_sigqueue(struct k_itimer *tmr)
+{
+	struct sigqueue *q = tmr->sigq;
+	int sig = q->info.si_signo;
 	struct task_struct *t;
 	unsigned long flags;
 	int ret, result;
 
-	if (WARN_ON_ONCE(!(q->flags & SIGQUEUE_PREALLOC)))
-		return 0;
-	if (WARN_ON_ONCE(q->info.si_code != SI_TIMER))
-		return 0;
-
-	ret = -1;
-	rcu_read_lock();
+	guard(rcu)();
 
-	/*
-	 * This function is used by POSIX timers to deliver a timer signal.
-	 * Where type is PIDTYPE_PID (such as for timers with SIGEV_THREAD_ID
-	 * set), the signal must be delivered to the specific thread (queues
-	 * into t->pending).
-	 *
-	 * Where type is not PIDTYPE_PID, signals must be delivered to the
-	 * process. In this case, prefer to deliver to current if it is in
-	 * the same thread group as the target process, which avoids
-	 * unnecessarily waking up a potentially idle task.
-	 */
-	t = pid_task(pid, type);
+	t = posixtimer_get_target(tmr);
 	if (!t)
-		goto ret;
-	if (type != PIDTYPE_PID && same_thread_group(t, current))
-		t = current;
+		return -1;
+
 	if (!likely(lock_task_sighand(t, &flags)))
-		goto ret;
+		return -1;
 
 	/*
 	 * Update @q::info::si_sys_private for posix timer signals with
@@ -1988,30 +2002,24 @@ int send_sigqueue(struct sigqueue *q, struct pid *pid, enum pid_type type, int s
 	 * decides based on si_sys_private whether to invoke
 	 * posixtimer_rearm() or not.
 	 */
-	q->info.si_sys_private = si_private;
+	q->info.si_sys_private = tmr->it_signal_seq;
 
 	ret = 1; /* the signal is ignored */
-	result = TRACE_SIGNAL_IGNORED;
-	if (!prepare_signal(sig, t, false))
+	if (!prepare_signal(sig, t, false)) {
+		result = TRACE_SIGNAL_IGNORED;
 		goto out;
+	}
 
 	ret = 0;
 	if (unlikely(!list_empty(&q->list))) {
 		result = TRACE_SIGNAL_ALREADY_PENDING;
 		goto out;
 	}
-
-	signalfd_notify(t, sig);
-	pending = (type != PIDTYPE_PID) ? &t->signal->shared_pending : &t->pending;
-	list_add_tail(&q->list, &pending->list);
-	sigaddset(&pending->signal, sig);
-	complete_signal(sig, t, type);
+	posixtimer_queue_sigqueue(q, t, tmr->it_pid_type);
 	result = TRACE_SIGNAL_DELIVERED;
 out:
-	trace_signal_generate(sig, &q->info, t, type != PIDTYPE_PID, result);
+	trace_signal_generate(sig, &q->info, t, tmr->it_pid_type != PIDTYPE_PID, result);
 	unlock_task_sighand(t, &flags);
-ret:
-	rcu_read_unlock();
 	return ret;
 }
 #endif /* CONFIG_POSIX_TIMERS */
diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index f18d64c7cd3b..0901ed9ca183 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -307,7 +307,7 @@ int posix_timer_queue_signal(struct k_itimer *timr)
 
 	timr->it_status = state;
 
-	ret = send_sigqueue(timr->sigq, timr->it_pid, timr->it_pid_type, timr->it_signal_seq);
+	ret = posixtimer_send_sigqueue(timr);
 	/* If we failed to send the signal the timer stops. */
 	return ret > 0;
 }