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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	jstultz@google.com, Stephen Boyd <sboyd@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Marcel Holtmann <marcel@holtmann.org>,
	Johan Hedberg <johan.hedberg@gmail.com>,
	Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
	Eric Dumazet <edumazet@google.com>,
	Guenter Roeck <linux@roeck-us.net>
Subject: Re: [RFC][PATCH] timers: Add del_time_free() to be called before freeing timers
Date: Fri, 8 Apr 2022 15:00:43 -1000	[thread overview]
Message-ID: <CAHk-=wg6ZTjCoWev039ijHkzJGOE8v1Psc=yDANkt5r3GBxc0w@mail.gmail.com> (raw)
In-Reply-To: <20220408204925.16361b44@rorschach.local.home>

On Fri, Apr 8, 2022 at 2:49 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> Hmm, well, I'm not sure it would work for all architectures, but what
> about the MSB?  Setting it to zero on "shutdown"?

Let's just clear the whole thing for now. We don't actually _have_ any
timer_restart() cases yet.

I was more thinking that we might have situations where "I don't want
to race with timers, but I also don't want to take an interrupt-safe
lock" makes a lot of sense.

Most people most definitely are just about "module unload" and similar
issues, where it goes along with doing "task_work_cancel()" and
friends.

I do wonder if we want some way to shut down new timers that doesn't
actually wait for old ones to finish.

We've had issues with some code not being able to use del_timer_sync()
simply because they hold locks that could deadlock with any "wait for
running timer" situation.

Those places couldn't use a synchronous cancel operation either, for
the same reason.

I'm not sure a "make sure no future timers can start" operation is
sensible on its own, though. I can't think of a situation where that
wouldn't also need that "wait for existing ones to finish".

                       Linus

  reply	other threads:[~2022-04-09  1:01 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-07 20:17 [RFC][PATCH] timers: Add del_time_free() to be called before freeing timers Steven Rostedt
2022-04-07 21:58 ` Guenter Roeck
2022-04-07 22:51   ` Steven Rostedt
2022-04-08  0:58     ` Guenter Roeck
2022-04-08  1:36       ` Steven Rostedt
2022-04-08 10:37 ` Thomas Gleixner
2022-04-08 12:33   ` Steven Rostedt
2022-04-08 15:55   ` Steven Rostedt
2022-04-08 17:33   ` Linus Torvalds
2022-04-08 20:10     ` Steven Rostedt
2022-04-08 20:26       ` Steven Rostedt
2022-04-08 23:18       ` Linus Torvalds
2022-04-08 20:29     ` Thomas Gleixner
2022-04-08 20:58       ` Steven Rostedt
2022-04-08 21:46         ` Thomas Gleixner
2022-04-08 21:59           ` Steven Rostedt
2022-04-09  0:22       ` Steven Rostedt
2022-04-09  0:30         ` Linus Torvalds
2022-04-09  0:49           ` Steven Rostedt
2022-04-09  1:00             ` Linus Torvalds [this message]
2022-04-09  1:14               ` Steven Rostedt
2022-11-24 14:16 ` [tip: timers/core] timers: Provide timer_shutdown[_sync]() tip-bot2 for Thomas Gleixner
2022-11-24 14:16 ` [tip: timers/core] timers: Add shutdown mechanism to the internal functions tip-bot2 for Thomas Gleixner
2022-11-24 14:16 ` [tip: timers/core] timers: Split [try_to_]del_timer[_sync]() to prepare for shutdown mode tip-bot2 for Thomas Gleixner
2022-11-24 14:16 ` [tip: timers/core] timers: Silently ignore timers with a NULL function tip-bot2 for Thomas Gleixner
2022-11-24 14:16 ` [tip: timers/core] timers: Use del_timer_sync() even on UP tip-bot2 for Thomas Gleixner

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