Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [PATCH v6 4/6] timers: Add timer_shutdown_sync() to be called before freeing timers | Date | Mon, 14 Nov 2022 20:13:28 +0100 |
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On Mon, Nov 14 2022 at 08:36, Steven Rostedt wrote: > On Mon, 14 Nov 2022 01:33:25 +0100 > Thomas Gleixner <tglx@linutronix.de> wrote: >> https://lore.kernel.org/all/87v8vjiaih.ffs@tglx/ >> > I'm not sure what you mean by that. The idea is that once timer_shutdown() > is called, we still warn on re-arming the timer.
That's the whole point. As Linus and I discussed in that thread:
"That would mean, that we still check the function pointer for NULL without warning and just return. That would indeed be a good argument for not having the warning at all."
and as I demonstrated you on the example of the BT driver which you "fixed" this is the only sensible way to handle this.
The warning does not buy us anything, unless you want to go and amend all the usage sites which trigger it with 'if (mystruct->shutdown)' conditionals.
It's very similar to the work->canceling logic for kthreads that Linus mentioned in this thread which prevents that the work timer is rearmed concurrently. The difference is that timer_shutdown() is a final decision which renders the timer unusable unless it is explicitely reinitialized.
But that's mostly a matter of documentation and it has to be made clear that nothing in a shutdown path which has the BT pattern:
timer_shutdown(); destroy_workqueue();
relies on the timer being functional after the shutdown point. I'm pretty sure that the vast majority of such use cases do not care, but given the size of the driver zoo I'm also sure that you'll find at least one which depends on the timer working accross teardown.
Thanks,
tglx
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