linux-kernel - [patch V7 14/21] posix-timers: Move sequence logic into struct k

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Message-ID: <20241105064213.852619866@linutronix.de>
Date: Tue,  5 Nov 2024 09:14:48 +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 14/21] posix-timers: Move sequence logic into struct
 k_itimer

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

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>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
V6: Update the comment in siginfo.h
V5: New patch
---
 include/linux/posix-timers.h       |    2 ++
 include/uapi/asm-generic/siginfo.h |    2 +-
 kernel/signal.c                    |    8 +++-----
 kernel/time/posix-timers.c         |    5 +----
 4 files changed, 7 insertions(+), 10 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/include/uapi/asm-generic/siginfo.h
+++ b/include/uapi/asm-generic/siginfo.h
@@ -46,7 +46,7 @@ union __sifields {
 		__kernel_timer_t _tid;	/* timer id */
 		int _overrun;		/* overrun count */
 		sigval_t _sigval;	/* same as below */
-		int _sys_private;       /* not to be passed to user */
+		int _sys_private;       /* Not used by the kernel. Historic leftover. Always 0. */
 	} _timer;
 
 	/* POSIX.1b signals */
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1976,12 +1976,10 @@ 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;
 
 	ret = 1; /* the signal is ignored */
 	if (!prepare_signal(sig, t, false)) {
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -259,7 +259,7 @@ static bool __posixtimer_deliver_signal(
 	 * since the signal was queued. In either case, don't rearm and
 	 * drop the signal.
 	 */
-	if (timr->it_signal_seq != info->si_sys_private || WARN_ON_ONCE(!timr->it_signal))
+	if (timr->it_signal_seq != timr->it_sigqueue_seq || WARN_ON_ONCE(!timr->it_signal))
 		return false;
 
 	if (!timr->it_interval || WARN_ON_ONCE(timr->it_status != POSIX_TIMER_REQUEUE_PENDING))
@@ -297,9 +297,6 @@ 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;
 }