Re: [RFC PATCH 1/7] drivers: base: Add resource managed version of delayed work init

From: Hans de Goede <hdegoede@redhat.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>,
	mazziesaccount@gmail.com, "Rafael J. Wysocki" <rafael@kernel.org>,
	MyungJoo Ham <myungjoo.ham@samsung.com>,
	Chanwoo Choi <cw00.choi@samsung.com>,
	Andy Gross <agross@kernel.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Jean Delvare <jdelvare@suse.com>,
	Guenter Roeck <linux@roeck-us.net>,
	Mark Gross <mgross@linux.intel.com>,
	Sebastian Reichel <sre@kernel.org>, Chen-Yu Tsai <wens@csie.org>,
	Liam Girdwood <lgirdwood@gmail.com>,
	Mark Brown <broonie@kernel.org>,
	Wim Van Sebroeck <wim@linux-watchdog.org>,
	Saravana Kannan <saravanak@google.com>,
	Heikki Krogerus <heikki.krogerus@linux.intel.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Joerg Roedel <jroedel@suse.de>,
	Dan Williams <dan.j.williams@intel.com>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	linux-hwmon@vger.kernel.org, platform-driver-x86@vger.kernel.org,
	linux-pm@vger.kernel.org, linux-watchdog@vger.kernel.org
Subject: Re: [RFC PATCH 1/7] drivers: base: Add resource managed version of delayed work init
Date: Sat, 13 Feb 2021 15:52:06 +0100	[thread overview]
Message-ID: <529a5122-ff3a-2af0-52ed-b13216fa49d1@redhat.com> (raw)
In-Reply-To: <eecf8ad6-a99d-8ad0-fc7e-f87d015add3f@redhat.com>

Hi,

On 2/13/21 3:38 PM, Hans de Goede wrote:
> Hi,
> 
> On 2/13/21 2:33 PM, Greg Kroah-Hartman wrote:

<snip>

> Having this new devm_delayed_work_autocancel() helper will allow a
> bunch of drivers to move away from mixing the 2, which is a good thing
> in my book.
> 
> As I said above I believe that having devm_delayed_work_autocancel() (1)
> in our toolbox will be a good thing to have. Driver authors can then choose
> to use it; or they can choose to not use it if they don't like it.
> 
> I know that the reason why I did not use it in the
> drivers/extcon/extcon-intel-int3496.c driver is because it was not available
> if it had been available then I would definitely have used it, as it avoids the
> mixing of resource-management styles which that driver is currently doing.
> 
> And I think that that is what this is ultimately about, there are 2 styles
> of resource-management:
> 
> 1. manual
> 2. devm based
> 
> And they both have their pros and cons, problems mostly arise when mixing them
> and adding new devm helpers for commonly used cleanup patterns is a good thing
> as it helps to get rid of mixing these 2 styles in a single driver.

I just noticed that I forgot to fill in the (1) footnote above:

1) And we probably will want one for non delayed work items to: devm_work_autocancel(),
but lets cross that bridge when we get there.

Also when reviewing: "[RFC PATCH 2/7] extconn: Clean-up few drivers by using managed work init"
I noticed that the extcon-qcom-spmi-misc.c and extcon-palmas.c follow the same standard
pattern of having an IRQ which queues a delayed work and they both miss the devm_free_irq
call before the cancel_delayed_work_sync() on driver release. So just patch 2/7 here
fixes 3 driver-release race conditions (fixing 3/4 drivers which it touches) as a
bonus to the code-cleanup which it does.

So as this clearly seems to be fixing a bunch of bugs, by simply completely removing the
buggy code driver remove callbacks, this really seems like a good idea to me.

Regards,

Hans