linux-kernel - Re: [patch V5 21/26] posix-timers: Handle ignored list on delete and exit

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Message-ID: <ZyJng49tJutCM62d@localhost.localdomain>
Date: Wed, 30 Oct 2024 18:06:11 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	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: Re: [patch V5 21/26] posix-timers: Handle ignored list on delete and
 exit

Le Tue, Oct 01, 2024 at 10:42:29AM +0200, Thomas Gleixner a écrit :
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> To handle posix timer signals on sigaction(SIG_IGN) properly, the timers
> will be queued on a separate ignored list.
> 
> Add the necessary cleanup code for timer_delete() and exit_itimers().
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  include/linux/posix-timers.h |    4 +++-
>  kernel/time/posix-timers.c   |   20 ++++++++++++++++++++
>  2 files changed, 23 insertions(+), 1 deletion(-)
> ---
> --- a/include/linux/posix-timers.h
> +++ b/include/linux/posix-timers.h
> @@ -152,7 +152,8 @@ static inline void posix_cputimers_init_
>  
>  /**
>   * struct k_itimer - POSIX.1b interval timer structure.
> - * @list:		List head for binding the timer to signals->posix_timers
> + * @list:		List node for binding the timer to tsk::signal::posix_timers
> + * @ignored_list:	List node for tracking ignored timers in tsk::signal::ignored_posix_timers
>   * @t_hash:		Entry in the posix timer hash table
>   * @it_lock:		Lock protecting the timer
>   * @kclock:		Pointer to the k_clock struct handling this timer
> @@ -176,6 +177,7 @@ static inline void posix_cputimers_init_
>   */
>  struct k_itimer {
>  	struct hlist_node	list;
> +	struct hlist_node	ignored_list;
>  	struct hlist_node	t_hash;
>  	spinlock_t		it_lock;
>  	const struct k_clock	*kclock;
> --- a/kernel/time/posix-timers.c
> +++ b/kernel/time/posix-timers.c
> @@ -1031,6 +1031,18 @@ int common_timer_del(struct k_itimer *ti
>  	return 0;
>  }
>  
> +/*
> + * If the deleted timer is on the ignored list, remove it and
> + * drop the associated reference.
> + */
> +static inline void posix_timer_cleanup_ignored(struct k_itimer *tmr)
> +{
> +	if (!hlist_unhashed(&tmr->ignored_list)) {
> +		hlist_del_init(&tmr->ignored_list);
> +		posixtimer_putref(tmr);
> +	}
> +}
> +
>  static inline int timer_delete_hook(struct k_itimer *timer)
>  {
>  	const struct k_clock *kc = timer->kclock;
> @@ -1063,6 +1075,7 @@ SYSCALL_DEFINE1(timer_delete, timer_t, t
>  
>  	spin_lock(&current->sighand->siglock);
>  	hlist_del(&timer->list);
> +	posix_timer_cleanup_ignored(timer);
>  	spin_unlock(&current->sighand->siglock);
>  	/*
>  	 * A concurrent lookup could check timer::it_signal lockless. It
> @@ -1114,6 +1127,8 @@ static void itimer_delete(struct k_itime
>  	}
>  	hlist_del(&timer->list);
>  
> +	posix_timer_cleanup_ignored(timer);
> +
>  	/*
>  	 * Setting timer::it_signal to NULL is technically not required
>  	 * here as nothing can access the timer anymore legitimately via
> @@ -1146,6 +1161,11 @@ void exit_itimers(struct task_struct *ts
>  	/* The timers are not longer accessible via tsk::signal */
>  	while (!hlist_empty(&timers))
>  		itimer_delete(hlist_entry(timers.first, struct k_itimer, list));
> +
> +	/* Mop up timers which are on the ignored list */
> +	hlist_move_list(&tsk->signal->ignored_posix_timers, &timers);
> +	while (!hlist_empty(&timers))
> +		posix_timer_cleanup_ignored(hlist_entry(timers.first, struct k_itimer, list));

The ignored timers should have all been removed on timer_delete() and
itimer_delete(), right?

So should it be instead:

   WARN_ON_ONCE(!hlist_empty(&tsk->signal->ignored_posix_timers))

?

Thanks.

>  }
>  
>  SYSCALL_DEFINE2(clock_settime, const clockid_t, which_clock,
>