linux-kernel - [patch v4 22/27] posix-timers: Handle ignored list on delete and exit

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Message-ID: <20240927084818.250962485@linutronix.de>
Date: Fri, 27 Sep 2024 10:49:06 +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 v4 22/27] posix-timers: Handle ignored list on delete and exit

From: Thomas Gleixner <tglx@...utronix.de>

To handle posix timer signals on sigaction(SIG_IGN) properly, the timers
will be queued on a separate ignored list.

Add the necessary cleanup code for timer_delete() and exit_itimers().

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

---
 include/linux/posix-timers.h |  4 +++-
 kernel/time/posix-timers.c   | 20 ++++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)
---
diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index ddd7ccd9ba77..efab1ef7a7fe 100644
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -151,7 +151,8 @@ static inline void posix_cputimers_init_work(void) { }
 
 /**
  * struct k_itimer - POSIX.1b interval timer structure.
- * @list:		List head for binding the timer to signals->posix_timers
+ * @list:		List node for binding the timer to tsk::signal::posix_timers
+ * @ignored_list:	List node for tracking ignored timers in tsk::signal::ignored_posix_timers
  * @t_hash:		Entry in the posix timer hash table
  * @it_lock:		Lock protecting the timer
  * @kclock:		Pointer to the k_clock struct handling this timer
@@ -174,6 +175,7 @@ static inline void posix_cputimers_init_work(void) { }
  */
 struct k_itimer {
 	struct hlist_node	list;
+	struct hlist_node	ignored_list;
 	struct hlist_node	t_hash;
 	spinlock_t		it_lock;
 	const struct k_clock	*kclock;
diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index b62e3ccb45ff..5a5967a01f53 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -1036,6 +1036,18 @@ int common_timer_del(struct k_itimer *timer)
 	return 0;
 }
 
+/*
+ * If the deleted timer is on the ignored list, remove it and
+ * drop the associated reference.
+ */
+static inline void posix_timer_cleanup_ignored(struct k_itimer *tmr)
+{
+	if (!hlist_unhashed(&tmr->ignored_list)) {
+		hlist_del_init(&tmr->ignored_list);
+		posixtimer_putref(tmr);
+	}
+}
+
 static inline int timer_delete_hook(struct k_itimer *timer)
 {
 	const struct k_clock *kc = timer->kclock;
@@ -1068,6 +1080,7 @@ SYSCALL_DEFINE1(timer_delete, timer_t, timer_id)
 
 	spin_lock(&current->sighand->siglock);
 	hlist_del(&timer->list);
+	posix_timer_cleanup_ignored(timer);
 	spin_unlock(&current->sighand->siglock);
 	/*
 	 * A concurrent lookup could check timer::it_signal lockless. It
@@ -1119,6 +1132,8 @@ static void itimer_delete(struct k_itimer *timer)
 	}
 	hlist_del(&timer->list);
 
+	posix_timer_cleanup_ignored(timer);
+
 	/*
 	 * Setting timer::it_signal to NULL is technically not required
 	 * here as nothing can access the timer anymore legitimately via
@@ -1151,6 +1166,11 @@ void exit_itimers(struct task_struct *tsk)
 	/* The timers are not longer accessible via tsk::signal */
 	while (!hlist_empty(&timers))
 		itimer_delete(hlist_entry(timers.first, struct k_itimer, list));
+
+	/* Mop up timers which are on the ignored list */
+	hlist_move_list(&tsk->signal->ignored_posix_timers, &timers);
+	while (!hlist_empty(&timers))
+		posix_timer_cleanup_ignored(hlist_entry(timers.first, struct k_itimer, list));
 }
 
 SYSCALL_DEFINE2(clock_settime, const clockid_t, which_clock,