linux-kernel - [patch V7 03/21] posix-timers: Make signal overrun accounting sensible

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Message-ID: <20241105064213.106738193@linutronix.de>
Date: Tue,  5 Nov 2024 09:14:32 +0100 (CET)
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 V7 03/21] posix-timers: Make signal overrun accounting
 sensible

The handling of the timer overrun in the signal code is inconsistent as it
takes previous overruns into account. This is just wrong as after the
reprogramming of a timer the overrun count starts over from a clean state,
i.e. 0.

Don't touch info::si_overrun in send_sigqueue() and only store the overrun
value at signal delivery time, which is computed from the timer itself
relative to the expiry time.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
V6: Fold the timer_overrun_to_int() cleanup from Frederic and remove all
    overrun fiddling from the signal path.
---
 kernel/signal.c            |    6 ------
 kernel/time/posix-timers.c |   11 ++++++-----
 2 files changed, 6 insertions(+), 11 deletions(-)
---

--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1968,15 +1968,9 @@ int send_sigqueue(struct sigqueue *q, st
 
 	ret = 0;
 	if (unlikely(!list_empty(&q->list))) {
-		/*
-		 * If an SI_TIMER entry is already queue just increment
-		 * the overrun count.
-		 */
-		q->info.si_overrun++;
 		result = TRACE_SIGNAL_ALREADY_PENDING;
 		goto out;
 	}
-	q->info.si_overrun = 0;
 
 	signalfd_notify(t, sig);
 	pending = (type != PIDTYPE_PID) ? &t->signal->shared_pending : &t->pending;
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -233,11 +233,12 @@ static __init int init_posix_timers(void
  * The siginfo si_overrun field and the return value of timer_getoverrun(2)
  * are of type int. Clamp the overrun value to INT_MAX
  */
-static inline int timer_overrun_to_int(struct k_itimer *timr, int baseval)
+static inline int timer_overrun_to_int(struct k_itimer *timr)
 {
-	s64 sum = timr->it_overrun_last + (s64)baseval;
+	if (timr->it_overrun_last > (s64)INT_MAX)
+		return INT_MAX;
 
-	return sum > (s64)INT_MAX ? INT_MAX : (int)sum;
+	return (int)timr->it_overrun_last;
 }
 
 static void common_hrtimer_rearm(struct k_itimer *timr)
@@ -280,7 +281,7 @@ bool posixtimer_deliver_signal(struct ke
 		timr->it_overrun = -1LL;
 		++timr->it_signal_seq;
 
-		info->si_overrun = timer_overrun_to_int(timr, info->si_overrun);
+		info->si_overrun = timer_overrun_to_int(timr);
 	}
 	ret = true;
 
@@ -774,7 +775,7 @@ SYSCALL_DEFINE1(timer_getoverrun, timer_
 	if (!timr)
 		return -EINVAL;
 
-	overrun = timer_overrun_to_int(timr, 0);
+	overrun = timer_overrun_to_int(timr);
 	unlock_timer(timr, flags);
 
 	return overrun;