linux-kernel - Re: [RFC][PATCH] timers: Add del_time_free() to be called before freeing timers

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Date:   Fri, 8 Apr 2022 20:22:30 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, jstultz@...gle.com,
        Stephen Boyd <sboyd@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Guenter Roeck <linux@...ck-us.net>
Subject: Re: [RFC][PATCH] timers: Add del_time_free() to be called before
 freeing timers

On Fri, 08 Apr 2022 22:29:58 +0200
Thomas Gleixner <tglx@...utronix.de> wrote:

> Well, you'd have to reinitialize it first before the explicit rearm
> because the shutdown cleared the function pointer or if we use a flag
> then the flag would prevent arming it again.

We could always use the LSB bit of the function as a "shutdown" flag, where:

timer_shutdown() {
	[..]
	timer->fn = (void *)((unsigned long)timer->fn | 1);
	[..]
}

timer_rearm() {
	[..]
	timer->fn = (void *)((unsigned long)timer->fn & ~1UL);
	[..]
}

mod_timer() {

	if ((unsigned long)timer->fn & 1)
		return -EBUSY?;

	[..]
}

-- Steve