linux-kernel - [patch V5 19/26] posix-timers: Move sequence logic into struct k

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Message-ID: <20241001083836.396279339@linutronix.de>
Date: Tue,  1 Oct 2024 10:42:26 +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 V5 19/26] posix-timers: Move sequence logic into struct
 k_itimer

The posix timer signal handling uses siginfo::si_sys_private for handling
the sequence counter check. That indirection is not longer required and the
sequence count value at signal queueing time can be stored in struct
k_itimer itself.

This removes the requirement of treating siginfo::si_sys_private special as
it's now always zero as the kernel does not touch it anymore.

Suggested-by: Eric W. Biederman <ebiederm@...ssion.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
V5: New patch
---
 include/linux/posix-timers.h |    2 ++
 kernel/signal.c              |    8 +++-----
 kernel/time/posix-timers.c   |    5 +----
 3 files changed, 6 insertions(+), 9 deletions(-)

--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -162,6 +162,7 @@ static inline void posix_cputimers_init_
  * @it_overrun:		The overrun counter for pending signals
  * @it_overrun_last:	The overrun at the time of the last delivered signal
  * @it_signal_seq:	Sequence count to control signal delivery
+ * @it_sigqueue_seq:	The sequence count at the point where the signal was queued
  * @it_sigev_notify:	The notify word of sigevent struct for signal delivery
  * @it_interval:	The interval for periodic timers
  * @it_signal:		Pointer to the creators signal struct
@@ -184,6 +185,7 @@ struct k_itimer {
 	s64			it_overrun;
 	s64			it_overrun_last;
 	unsigned int		it_signal_seq;
+	unsigned int		it_sigqueue_seq;
 	int			it_sigev_notify;
 	enum pid_type		it_pid_type;
 	ktime_t			it_interval;
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1968,12 +1968,10 @@ int posixtimer_send_sigqueue(struct k_it
 		return -1;
 
 	/*
-	 * Update @q::info::si_sys_private for posix timer signals with
-	 * sighand locked to prevent a race against dequeue_signal() which
-	 * decides based on si_sys_private whether to invoke
-	 * posixtimer_rearm() or not.
+	 * Update @tmr::sigqueue_seq for posix timer signals with sighand
+	 * locked to prevent a race against dequeue_signal().
 	 */
-	q->info.si_sys_private = tmr->it_signal_seq;
+	tmr->it_sigqueue_seq = tmr->it_signal_seq;
 
 	/*
 	 * Set the overrun count to zero unconditionally. The posix timer
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -272,7 +272,7 @@ bool posixtimer_deliver_signal(struct ke
 	 * since the signal was queued. In either case, don't rearm and
 	 * drop the signal.
 	 */
-	if (!timr->it_signal || timr->it_signal_seq != info->si_sys_private)
+	if (!timr->it_signal || timr->it_signal_seq != timr->it_sigqueue_seq)
 		goto out_unlock;
 
 	if (timr->it_interval && timr->it_status == POSIX_TIMER_REQUEUE_PENDING) {
@@ -293,9 +293,6 @@ bool posixtimer_deliver_signal(struct ke
 	posixtimer_putref(timr);
 
 	spin_lock(&current->sighand->siglock);
-
-	/* Don't expose the si_sys_private value to userspace */
-	info->si_sys_private = 0;
 	return ret;
 }