linux-kernel - [patch v6 10/20] signal: Replace resched

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Message-ID: <20241031154425.182629074@linutronix.de>
Date: Thu, 31 Oct 2024 16:46:35 +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 v6 10/20] signal: Replace resched_timer logic

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

In preparation for handling ignored posix timer signals correctly and
embedding the sigqueue struct into struct k_itimer, hand down a pointer to
the sigqueue struct into posix_timer_deliver_signal() instead of just
having a boolean flag.

No functional change.

Suggested-by: Eric W. Biederman <ebiederm@...ssion.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
V6: NULLify timer_sigq after again: in dequeue_signal() - Frederic
V5: New patch
---
 include/linux/posix-timers.h |    5 +++--
 kernel/signal.c              |   32 ++++++++++++++++++++------------
 kernel/time/posix-timers.c   |    2 +-
 3 files changed, 24 insertions(+), 15 deletions(-)

--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -110,7 +110,7 @@ static inline void posix_cputimers_rt_wa
 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);
+bool posixtimer_deliver_signal(struct kernel_siginfo *info, struct sigqueue *timer_sigq);
 void posixtimer_free_timer(struct k_itimer *timer);
 
 /* Init task static initializer */
@@ -135,7 +135,8 @@ static inline void posix_cputimers_init(
 static inline void posix_cputimers_group_init(struct posix_cputimers *pct,
 					      u64 cpu_limit) { }
 static inline void posixtimer_rearm_itimer(struct task_struct *p) { }
-static inline bool posixtimer_deliver_signal(struct kernel_siginfo *info) { return false; }
+static inline bool posixtimer_deliver_signal(struct kernel_siginfo *info,
+					     struct sigqueue *timer_sigq) { return false; }
 static inline void posixtimer_free_timer(struct k_itimer *timer) { }
 #endif
 
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -545,7 +545,7 @@ bool unhandled_signal(struct task_struct
 }
 
 static void collect_signal(int sig, struct sigpending *list, kernel_siginfo_t *info,
-			   bool *resched_timer)
+			   struct sigqueue **timer_sigq)
 {
 	struct sigqueue *q, *first = NULL;
 
@@ -568,10 +568,17 @@ static void collect_signal(int sig, stru
 		list_del_init(&first->list);
 		copy_siginfo(info, &first->info);
 
-		*resched_timer = (first->flags & SIGQUEUE_PREALLOC) &&
-				 (info->si_code == SI_TIMER);
-
-		__sigqueue_free(first);
+		/*
+		 * posix-timer signals are preallocated and freed when the
+		 * timer goes away. Either directly or by clearing
+		 * SIGQUEUE_PREALLOC so that the next delivery will free
+		 * them. Spare the extra round through __sigqueue_free()
+		 * which is ignoring preallocated signals.
+		 */
+		if (unlikely((first->flags & SIGQUEUE_PREALLOC) && (info->si_code == SI_TIMER)))
+			*timer_sigq = first;
+		else
+			__sigqueue_free(first);
 	} else {
 		/*
 		 * Ok, it wasn't in the queue.  This must be
@@ -588,12 +595,12 @@ static void collect_signal(int sig, stru
 }
 
 static int __dequeue_signal(struct sigpending *pending, sigset_t *mask,
-			kernel_siginfo_t *info, bool *resched_timer)
+			    kernel_siginfo_t *info, struct sigqueue **timer_sigq)
 {
 	int sig = next_signal(pending, mask);
 
 	if (sig)
-		collect_signal(sig, pending, info, resched_timer);
+		collect_signal(sig, pending, info, timer_sigq);
 	return sig;
 }
 
@@ -605,18 +612,19 @@ static int __dequeue_signal(struct sigpe
 int dequeue_signal(sigset_t *mask, kernel_siginfo_t *info, enum pid_type *type)
 {
 	struct task_struct *tsk = current;
-	bool resched_timer = false;
+	struct sigqueue *timer_sigq;
 	int signr;
 
 	lockdep_assert_held(&tsk->sighand->siglock);
 
 again:
 	*type = PIDTYPE_PID;
-	signr = __dequeue_signal(&tsk->pending, mask, info, &resched_timer);
+	timer_sigq = NULL;
+	signr = __dequeue_signal(&tsk->pending, mask, info, &timer_sigq);
 	if (!signr) {
 		*type = PIDTYPE_TGID;
 		signr = __dequeue_signal(&tsk->signal->shared_pending,
-					 mask, info, &resched_timer);
+					 mask, info, &timer_sigq);
 
 		if (unlikely(signr == SIGALRM))
 			posixtimer_rearm_itimer(tsk);
@@ -642,8 +650,8 @@ int dequeue_signal(sigset_t *mask, kerne
 		current->jobctl |= JOBCTL_STOP_DEQUEUED;
 	}
 
-	if (IS_ENABLED(CONFIG_POSIX_TIMERS) && unlikely(resched_timer)) {
-		if (!posixtimer_deliver_signal(info))
+	if (IS_ENABLED(CONFIG_POSIX_TIMERS) && unlikely(timer_sigq)) {
+		if (!posixtimer_deliver_signal(info, timer_sigq))
 			goto again;
 	}
 
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -254,7 +254,7 @@ static void common_hrtimer_rearm(struct
  * 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)
+bool posixtimer_deliver_signal(struct kernel_siginfo *info, struct sigqueue *timer_sigq)
 {
 	struct k_itimer *timr;
 	unsigned long flags;