linux-kernel - [patch V2 29/50] posix-timers: Drop signal if timer has been deleted or reprogrammed

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Message-ID: <20240410165552.772386179@linutronix.de>
Date: Thu, 11 Apr 2024 00:47:03 +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 V2 29/50] posix-timers: Drop signal if timer has been deleted
 or reprogrammed

No point in delivering a signal from the past. POSIX does not specify the
behaviour here:

 - "The effect of disarming or resetting a timer with pending expiration
    notifications is unspecified."

 - "The disposition of pending signals for the deleted timer is unspecified."

In both cases it is reasonable to expect that pending signals are
discarded. Especially in the reprogramming case it does not make sense to
account for previous overruns or to deliver a signal for a timer which has
been disarmed.

Drop the signal as that is conistent and understandable behaviour.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/time/posix-timers.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -250,14 +250,14 @@ static void common_hrtimer_rearm(struct
 }
 
 /*
- * This function is called from the signal delivery code if
- * info::si_sys_private is not zero, which indicates that the timer has to
- * be rearmed. Restart the timer and update info::si_overrun.
+ * This function is called from the signal delivery code. It decides
+ * whether the signal should be dropped and rearms interval timers.
  */
 bool posixtimer_deliver_signal(struct kernel_siginfo *info)
 {
 	struct k_itimer *timr;
 	unsigned long flags;
+	bool ret = false;
 
 	/*
 	 * Release siglock to ensure proper locking order versus
@@ -279,6 +279,7 @@ bool posixtimer_deliver_signal(struct ke
 
 		info->si_overrun = timer_overrun_to_int(timr, info->si_overrun);
 	}
+	ret = true;
 
 	unlock_timer(timr, flags);
 out:
@@ -286,7 +287,7 @@ bool posixtimer_deliver_signal(struct ke
 
 	/* Don't expose the si_sys_private value to userspace */
 	info->si_sys_private = 0;
-	return true;
+	return ret;
 }
 
 int posix_timer_queue_signal(struct k_itimer *timr)