linux-kernel - [patch V3 48/51] signal: Queue ignored posixtimers on ignore list

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Message-ID: <20240610164028.472552548@linutronix.de>
Date: Mon, 10 Jun 2024 18:43:04 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Anna-Maria Behnsen <anna-maria@...utronix.de>,
 Frederic Weisbecker <frederic@...nel.org>,
 John Stultz <jstultz@...gle.com>,
 Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...nel.org>,
 Stephen Boyd <sboyd@...nel.org>,
 Eric Biederman <ebiederm@...ssion.com>,
 Oleg Nesterov <oleg@...hat.com>
Subject: [patch V3 48/51] signal: Queue ignored posixtimers on ignore list

Queue posixtimers which have their signal ignored on the ignored list:

   1) When the timer fires and the signal has SIG_IGN set

   2) When SIG_IGN is installed via sigaction() and a timer signal
      is queued

This completes the SIG_IGN handling and such timers are not longer self
rearmed which avoids pointless wakeups.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/signal.c |   44 ++++++++++++++++++++++++++++++++++++--------
 1 file changed, 36 insertions(+), 8 deletions(-)

--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -722,6 +722,16 @@ void signal_wake_up_state(struct task_st
 		kick_process(t);
 }
 
+static inline void posixtimer_sig_ignore(struct task_struct *tsk, struct sigqueue *q);
+
+static void sigqueue_free_ignored(struct task_struct *ptmr_tsk, struct sigqueue *q)
+{
+	if (likely(!ptmr_tsk || q->info.si_code != SI_TIMER))
+		__sigqueue_free(q);
+	else
+		posixtimer_sig_ignore(ptmr_tsk, q);
+}
+
 /*
  * Remove signals in mask from the pending set and queue.
  *
@@ -740,7 +750,7 @@ static void flush_sigqueue_mask(sigset_t
 	list_for_each_entry_safe(q, n, &s->list, list) {
 		if (sigismember(mask, q->info.si_signo)) {
 			list_del_init(&q->list);
-			__sigqueue_free(q);
+			sigqueue_free_ignored(ptmr_tsk, q);
 		}
 	}
 }
@@ -1964,9 +1974,8 @@ int posixtimer_send_sigqueue(struct k_it
 	int sig = q->info.si_signo;
 	struct task_struct *t;
 	unsigned long flags;
-	int ret, result;
+	int result;
 
-	ret = -1;
 	rcu_read_lock();
 
 	t = posixtimer_get_target(tmr);
@@ -2012,13 +2021,24 @@ int posixtimer_send_sigqueue(struct k_it
 	 */
 	q->info.si_overrun = 0;
 
-	ret = 1; /* the signal is ignored */
 	if (!prepare_signal(sig, t, false)) {
 		result = TRACE_SIGNAL_IGNORED;
+
+		/* Paranoia check. Try to survive. */
+		if (WARN_ON_ONCE(!list_empty(&q->list)))
+			goto out;
+
+		if (hlist_unhashed(&tmr->ignored_list)) {
+			hlist_add_head(&tmr->ignored_list, &t->signal->ignored_posix_timers);
+			posixtimer_sigqueue_getref(q);
+		}
 		goto out;
 	}
 
-	ret = 0;
+	/* This should never happen and leaks a reference count */
+	if (WARN_ON_ONCE(!hlist_unhashed(&tmr->ignored_list)))
+		hlist_del_init(&tmr->ignored_list);
+
 	if (unlikely(!list_empty(&q->list))) {
 		/* This holds a reference count already */
 		result = TRACE_SIGNAL_ALREADY_PENDING;
@@ -2033,7 +2053,14 @@ int posixtimer_send_sigqueue(struct k_it
 	unlock_task_sighand(t, &flags);
 ret:
 	rcu_read_unlock();
-	return ret;
+	return 0;
+}
+
+static inline void posixtimer_sig_ignore(struct task_struct *tsk, struct sigqueue *q)
+{
+	struct k_itimer *tmr = container_of(q, struct k_itimer, sigq);
+
+	hlist_add_head(&tmr->ignored_list, &tsk->signal->ignored_posix_timers);
 }
 
 static void posixtimer_sig_unignore(struct task_struct *tsk, int sig)
@@ -2082,6 +2109,7 @@ static void posixtimer_sig_unignore(stru
 	}
 }
 #else /* CONFIG_POSIX_TIMERS */
+static inline void posixtimer_sig_ignore(struct task_struct *tsk, struct sigqueue *q) { }
 static inline void posixtimer_sig_unignore(struct task_struct *tsk, int sig) { }
 #endif /* !CONFIG_POSIX_TIMERS */
 
@@ -4272,9 +4300,9 @@ int do_sigaction(int sig, struct k_sigac
 		if (sig_handler_ignored(sig_handler(p, sig), sig)) {
 			sigemptyset(&mask);
 			sigaddset(&mask, sig);
-			flush_sigqueue_mask(&mask, &p->signal->shared_pending, NULL);
+			flush_sigqueue_mask(&mask, &p->signal->shared_pending, p);
 			for_each_thread(p, t)
-				flush_sigqueue_mask(&mask, &t->pending, NULL);
+				flush_sigqueue_mask(&mask, &t->pending, p);
 		} else if (was_ignored) {
 			posixtimer_sig_unignore(p, sig);
 		}