linux-kernel - Re: [PATCH 05/21] can: bcm: Don't initialized an unused hrtimer

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Message-ID: <d6055bd1-c0c6-42ad-bb21-7ffad98c9882@hartkopp.net>
Date: Wed, 30 Oct 2024 15:51:40 +0100
From: Oliver Hartkopp <socketcan@...tkopp.net>
To: Nam Cao <namcao@...utronix.de>
Cc: Anna-Maria Behnsen <anna-maria@...utronix.de>,
 Frederic Weisbecker <frederic@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>,
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Miguel Ojeda <ojeda@...nel.org>, Kees Cook <kees@...nel.org>,
 linux-kernel@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH 05/21] can: bcm: Don't initialized an unused hrtimer



On 30.10.24 13:15, Nam Cao wrote:
> On Wed, Oct 30, 2024 at 11:49:49AM +0100, Oliver Hartkopp wrote:
>> On 28.10.24 08:29, Nam Cao wrote:
>>> The hrtimer "thrtimer" is not used for TX. But this timer is initialized
>>> regardless.
>>>
>>> Remove the hrtimer_init() for the unused hrtimer and change bcm_remove_op()
>>> to make sure hrtimer_cancel() is not called with the uninitialized hrtimer.
>>
>> NAK.
>>
>> There are several other occurrences of thrtimer that are not covered by
>> RX/TX distinction, where the second timer is canceled.
>>
>> This one-time init and cancel of an unused hrtimer costs nearly nothing and
>> is not even in any hot path.
>>
>> So this incomplete patch only adds complexity and potential error cases in
>> some 20 y/o code for nothing.
> 
> The "real" motivation is preparing to use hrtimer_setup() instead of
> hrtimer_init() [1] and deleting hrtimer_init() [2]. The new function
> mandates a callback function, and since the TX thrtimer doesn't have a
> callback function, hrtimer_setup() cannot be used.
> 
> Your concerns are also valid. So I can drop this patch, and use a dummy
> function to make hrtimer_setup() happy, like how it's done for the rt2x00
> driver [3]. It will make the driver a bit ugly, but it's obvious that it
> won't cause any regression.

Many thanks for your efforts!
That's a good approach!

Best regards,
Oliver

> 
> Best regards,
> Nam
> 
> [1] https://lore.kernel.org/lkml/e4ce3a3a28625d54ef93e47bfb02f7ffb741758a.1729865232.git.namcao@linutronix.de/
> [2] https://lore.kernel.org/lkml/7bde2762d82d30dab184c7a747e76afc41208da0.1729865740.git.namcao@linutronix.de/
> [3] https://lore.kernel.org/lkml/49f2bce487f56eb2a3ff572ea6d7de0a43560c0f.1729865232.git.namcao@linutronix.de/