linux-kernel - Re: [patch V3 16/18] posix-timers: Dont iterate /proc/$PID/timers with sighand:: Siglock held

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Message-ID: <Z8zHAwpFDECRYVC6@grain>
Date: Sun, 9 Mar 2025 01:38:59 +0300
From: Cyrill Gorcunov <gorcunov@...il.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Frederic Weisbecker <frederic@...nel.org>,
	Benjamin Segall <bsegall@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Andrey Vagin <avagin@...nvz.org>,
	Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [patch V3 16/18] posix-timers: Dont iterate /proc/$PID/timers
 with sighand:: Siglock held

On Sat, Mar 08, 2025 at 05:48:45PM +0100, Thomas Gleixner wrote:
...
>  
>  static int show_timer(struct seq_file *m, void *v)
>  {
> -	struct k_itimer *timer;
> -	struct timers_private *tp = m->private;
> -	int notify;
>  	static const char * const nstr[] = {
> +		[SIGEV_SIGNAL]	= "signal",
> +		[SIGEV_NONE]	= "none",
> +		[SIGEV_THREAD]	= "thread",
>  	};
>  
...
> -	seq_printf(m, "notify: %s/%s.%d\n",
> -		   nstr[notify & ~SIGEV_THREAD_ID],
> +	seq_printf(m, "notify: %s/%s.%d\n", nstr[notify & ~SIGEV_THREAD_ID],
>  		   (notify & SIGEV_THREAD_ID) ? "tid" : "pid",
>  		   pid_nr_ns(timer->it_pid, tp->ns));
...

Btw this nstr[notify & ~SIGEV_THREAD_ID] has been always fishy since ~SIGEV_THREAD_ID
doesn't give a proper mask over nstr size :-) It just happen to work but if for some
reason ::it_sigev_notify get screwed we will get a surprise. I think later (not in this
series) we better provide an explicit bitwise mask here.

	Cyrill