[RFC PATCH v2 0/8] Add managed version of delayed work init

[RFC PATCH v2 0/8] Add managed version of delayed work init

[Matti Vaittinen]

It's not rare that device drivers need delayed work.
It's not rare that this work needs driver's data.

Often this means that driver must ensure the work is not queued when
driver is detached. Often it is done by ensuring new work is not added and
then calling cancel_delayed_work_sync() at remove(). In many cases this
may also require cleanup at probe error path - which is easy to forget.

Also the "by ensuring new work is not added" has a gotcha.

It is not strange to see devm managed IRQs scheduling (delayed) work.
Mixing this with manua wq clean-up is hard to do correctly because the
devm is likely to free the IRQ only after the remove() is ran. So manual
wq cancellation and devm-based IRQ management do not mix well - there is
a short(?) time-window after the wq clean-up when IRQs are still not
freed and may schedule new work.

When both WQs and IRQs are managed by devm things are likely to just
work. WQs should be initialized before IRQs (when IRQs need to schedule
work) and devm unwinds things in "FILO" order.

This series implements delayed wq cancellation on top of devm and replaces
the obvious cases where only thing remove call-back in a driver does is
cancelling the work. There might be other cases where we could switch
more than just work cancellation to use managed version and thus get rid
of remove or mixed (manual and devm) resource management.

This RFC does also introduce include/linux/devm-helpers.h file which
hopefully works as a place where this kind of helpers can be inlined.

Please see previous discussion here:
RFC v1:
https://lore.kernel.org/lkml/cover.1613216412.git.matti.vaittinen@fi.rohmeurope.com/

Changelog v2:
  - used correct terminology ("driver detach" instead of "exit, ...")
  - inlined the devm_delayed_work_autocancel() in a header
  - added Hans as a maintainer for the new header + myself as a reviewer
  - used devm_add_action() instead of using plain devres_add()

---

Matti Vaittinen (8):
  workqueue: Add resource managed version of delayed work init
  MAINTAINERS: Add entry for devm helpers
  extconn: Clean-up few drivers by using managed work init
  hwmon: raspberry-pi: Clean-up few drivers by using managed work init
  platform/x86: gpd pocket fan: Clean-up by using managed work init
  power: supply: Clean-up few drivers by using managed work init
  regulator: qcom_spmi-regulator: Clean-up by using managed work init
  watchdog: retu_wdt: Clean-up by using managed work init

 MAINTAINERS                                  |  6 +++
 drivers/extcon/extcon-gpio.c                 | 15 ++----
 drivers/extcon/extcon-intel-int3496.c        | 16 ++----
 drivers/extcon/extcon-palmas.c               | 17 +++----
 drivers/extcon/extcon-qcom-spmi-misc.c       | 17 +++----
 drivers/hwmon/raspberrypi-hwmon.c            | 17 +++----
 drivers/platform/x86/gpd-pocket-fan.c        | 17 +++----
 drivers/power/supply/axp20x_usb_power.c      | 15 ++----
 drivers/power/supply/bq24735-charger.c       | 18 +++----
 drivers/power/supply/ltc2941-battery-gauge.c | 20 +++-----
 drivers/power/supply/sbs-battery.c           | 16 ++----
 drivers/regulator/qcom_spmi-regulator.c      | 34 +++----------
 drivers/watchdog/retu_wdt.c                  | 22 +++-----
 include/linux/devm-helpers.h                 | 53 ++++++++++++++++++++
 14 files changed, 128 insertions(+), 155 deletions(-)
 create mode 100644 include/linux/devm-helpers.h


base-commit: a38fd8748464831584a19438cbb3082b5a2dab15
-- 
2.25.4


-- 
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =] 

[RFC PATCH v2 1/8] workqueue: Add resource managed version of delayed work init

[Matti Vaittinen]

A few drivers which need a delayed work-queue must cancel work at driver
detach. Some of those implement remove() solely for this purpose. Help
drivers to avoid unnecessary remove and error-branch implementation by
adding managed verision of delayed work initialization. This will also
help drivers to avoid mixing manual and devm based unwinding when other
resources are handled by devm.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
---
 include/linux/devm-helpers.h | 53 ++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 include/linux/devm-helpers.h

diff --git a/include/linux/devm-helpers.h b/include/linux/devm-helpers.h
new file mode 100644
index 000000000000..f64e0c9f3763
--- /dev/null
+++ b/include/linux/devm-helpers.h
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef __LINUX_DEVM_HELPERS_H
+#define __LINUX_DEVM_HELPERS_H
+
+/*
+ * Functions which do automatically cancel operations or release resources upon
+ * driver detach.
+ *
+ * These should be helpful to avoid mixing the manual and devm-based resource
+ * management which can be source of annoying, rarely occurring,
+ * hard-to-reproduce bugs.
+ *
+ * Please take into account that devm based cancellation may be performed some
+ * time after the remove() is ran.
+ *
+ * Thus mixing devm and manual resource management can easily cause problems
+ * when unwinding operations with dependencies. IRQ scheduling a work in a queue
+ * is typical example where IRQs are often devm-managed and WQs are manually
+ * cleaned at remove(). If IRQs are not manually freed at remove() (and this is
+ * often the case when we use devm for IRQs) we have a period of time after
+ * remove() - and before devm managed IRQs are freed - where new IRQ may fire
+ * and schedule a work item which won't be cancelled because remove() was
+ * already ran.
+ */
+
+#include <linux/device.h>
+#include <linux/workqueue.h>
+
+static inline void devm_delayed_work_drop(void *res)
+{
+	cancel_delayed_work_sync(res);
+}
+
+/**
+ * devm_delayed_work_autocancel - Resource-managed work allocation
+ * @dev: Device which lifetime work is bound to
+ * @pdata: work to be cancelled when driver is detached
+ *
+ * Initialize work which is automatically cancelled when driver is detached.
+ * A few drivers need delayed work which must be cancelled before driver
+ * is detached to avoid accessing removed resources.
+ * devm_delayed_work_autocancel() can be used to omit the explicit
+ * cancelleation when driver is detached.
+ */
+static inline int devm_delayed_work_autocancel(struct device *dev,
+					       struct delayed_work *w,
+					       work_func_t worker)
+{
+	INIT_DELAYED_WORK(w, worker);
+	return devm_add_action(dev, devm_delayed_work_drop, w);
+}
+
+#endif
-- 
2.25.4


-- 
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =] 

[RFC PATCH v2 2/8] MAINTAINERS: Add entry for devm helpers

[Matti Vaittinen]

Devm helper header containing small inline helpers was added.
Hans promised to maintain it.

Add Hans as maintainer and myself as designated reviewer.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
---
 MAINTAINERS | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index d92f85ca831d..ffcb00006e14 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5169,6 +5169,12 @@ M:	Torben Mathiasen <device@lanana.org>
 S:	Maintained
 W:	http://lanana.org/docs/device-list/index.html
 
+DEVICE RESOURCE MANAGEMENT HELPERS
+M:	Hans de Goede <hdegoede@redhat.com>
+R:	Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
+S:	Maintained
+F:	include/linux/devm-helpers.h
+
 DEVICE-MAPPER  (LVM)
 M:	Alasdair Kergon <agk@redhat.com>
 M:	Mike Snitzer <snitzer@redhat.com>
-- 
2.25.4


-- 
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =] 

[RFC PATCH v2 3/8] extconn: Clean-up few drivers by using managed work init

[Matti Vaittinen]

Few drivers implement remove call-back only for ensuring a delayed
work gets cancelled prior driver removal. Clean-up these by switching
to use devm_delayed_work_autocancel() instead.

Additionally, this helps avoiding mixing devm and manual resource
management and cleans up a (theoretical?) bug from extconn-palmas.c
and extcon-qcom-spmi-misc.c where (devm managed)IRQ might schedule
new work item after wq was cleaned at remove().

This change is compile-tested only. All testing is appreciated.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
---
 drivers/extcon/extcon-gpio.c           | 15 ++++-----------
 drivers/extcon/extcon-intel-int3496.c  | 16 ++++------------
 drivers/extcon/extcon-palmas.c         | 17 ++++++-----------
 drivers/extcon/extcon-qcom-spmi-misc.c | 17 ++++++-----------
 4 files changed, 20 insertions(+), 45 deletions(-)

diff --git a/drivers/extcon/extcon-gpio.c b/drivers/extcon/extcon-gpio.c
index c211222f5d0c..4105df74f2b0 100644
--- a/drivers/extcon/extcon-gpio.c
+++ b/drivers/extcon/extcon-gpio.c
@@ -9,6 +9,7 @@
  * (originally switch class is supported)
  */
 
+#include <linux/devm-helpers.h>
 #include <linux/extcon-provider.h>
 #include <linux/gpio/consumer.h>
 #include <linux/init.h>
@@ -112,7 +113,9 @@ static int gpio_extcon_probe(struct platform_device *pdev)
 	if (ret < 0)
 		return ret;
 
-	INIT_DELAYED_WORK(&data->work, gpio_extcon_work);
+	ret = devm_delayed_work_autocancel(dev, &data->work, gpio_extcon_work);
+	if (ret)
+		return ret;
 
 	/*
 	 * Request the interrupt of gpio to detect whether external connector
@@ -131,15 +134,6 @@ static int gpio_extcon_probe(struct platform_device *pdev)
 	return 0;
 }
 
-static int gpio_extcon_remove(struct platform_device *pdev)
-{
-	struct gpio_extcon_data *data = platform_get_drvdata(pdev);
-
-	cancel_delayed_work_sync(&data->work);
-
-	return 0;
-}
-
 #ifdef CONFIG_PM_SLEEP
 static int gpio_extcon_resume(struct device *dev)
 {
@@ -158,7 +152,6 @@ static SIMPLE_DEV_PM_OPS(gpio_extcon_pm_ops, NULL, gpio_extcon_resume);
 
 static struct platform_driver gpio_extcon_driver = {
 	.probe		= gpio_extcon_probe,
-	.remove		= gpio_extcon_remove,
 	.driver		= {
 		.name	= "extcon-gpio",
 		.pm	= &gpio_extcon_pm_ops,
diff --git a/drivers/extcon/extcon-intel-int3496.c b/drivers/extcon/extcon-intel-int3496.c
index 80c9abcc3f97..fb527c23639e 100644
--- a/drivers/extcon/extcon-intel-int3496.c
+++ b/drivers/extcon/extcon-intel-int3496.c
@@ -11,6 +11,7 @@
  */
 
 #include <linux/acpi.h>
+#include <linux/devm-helpers.h>
 #include <linux/extcon-provider.h>
 #include <linux/gpio/consumer.h>
 #include <linux/interrupt.h>
@@ -101,7 +102,9 @@ static int int3496_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	data->dev = dev;
-	INIT_DELAYED_WORK(&data->work, int3496_do_usb_id);
+	ret = devm_delayed_work_autocancel(dev, &data->work, int3496_do_usb_id);
+	if (ret)
+		return ret;
 
 	data->gpio_usb_id = devm_gpiod_get(dev, "id", GPIOD_IN);
 	if (IS_ERR(data->gpio_usb_id)) {
@@ -155,16 +158,6 @@ static int int3496_probe(struct platform_device *pdev)
 	return 0;
 }
 
-static int int3496_remove(struct platform_device *pdev)
-{
-	struct int3496_data *data = platform_get_drvdata(pdev);
-
-	devm_free_irq(&pdev->dev, data->usb_id_irq, data);
-	cancel_delayed_work_sync(&data->work);
-
-	return 0;
-}
-
 static const struct acpi_device_id int3496_acpi_match[] = {
 	{ "INT3496" },
 	{ }
@@ -177,7 +170,6 @@ static struct platform_driver int3496_driver = {
 		.acpi_match_table = int3496_acpi_match,
 	},
 	.probe = int3496_probe,
-	.remove = int3496_remove,
 };
 
 module_platform_driver(int3496_driver);
diff --git a/drivers/extcon/extcon-palmas.c b/drivers/extcon/extcon-palmas.c
index a2852bcc5f0d..d2c1a8b89c08 100644
--- a/drivers/extcon/extcon-palmas.c
+++ b/drivers/extcon/extcon-palmas.c
@@ -9,6 +9,7 @@
  * Author: Hema HK <hemahk@ti.com>
  */
 
+#include <linux/devm-helpers.h>
 #include <linux/module.h>
 #include <linux/interrupt.h>
 #include <linux/platform_device.h>
@@ -237,7 +238,11 @@ static int palmas_usb_probe(struct platform_device *pdev)
 			palmas_usb->sw_debounce_jiffies = msecs_to_jiffies(debounce);
 	}
 
-	INIT_DELAYED_WORK(&palmas_usb->wq_detectid, palmas_gpio_id_detect);
+	status = devm_delayed_work_autocancel(&pdev->dev,
+					      &palmas_usb->wq_detectid,
+					      palmas_gpio_id_detect);
+	if (status)
+		return status;
 
 	palmas->usb = palmas_usb;
 	palmas_usb->palmas = palmas;
@@ -359,15 +364,6 @@ static int palmas_usb_probe(struct platform_device *pdev)
 	return 0;
 }
 
-static int palmas_usb_remove(struct platform_device *pdev)
-{
-	struct palmas_usb *palmas_usb = platform_get_drvdata(pdev);
-
-	cancel_delayed_work_sync(&palmas_usb->wq_detectid);
-
-	return 0;
-}
-
 #ifdef CONFIG_PM_SLEEP
 static int palmas_usb_suspend(struct device *dev)
 {
@@ -422,7 +418,6 @@ static const struct of_device_id of_palmas_match_tbl[] = {
 
 static struct platform_driver palmas_usb_driver = {
 	.probe = palmas_usb_probe,
-	.remove = palmas_usb_remove,
 	.driver = {
 		.name = "palmas-usb",
 		.of_match_table = of_palmas_match_tbl,
diff --git a/drivers/extcon/extcon-qcom-spmi-misc.c b/drivers/extcon/extcon-qcom-spmi-misc.c
index 6b836ae62176..74d57d951b68 100644
--- a/drivers/extcon/extcon-qcom-spmi-misc.c
+++ b/drivers/extcon/extcon-qcom-spmi-misc.c
@@ -7,6 +7,7 @@
  * Stephen Boyd <stephen.boyd@linaro.org>
  */
 
+#include <linux/devm-helpers.h>
 #include <linux/extcon-provider.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
@@ -80,7 +81,11 @@ static int qcom_usb_extcon_probe(struct platform_device *pdev)
 	}
 
 	info->debounce_jiffies = msecs_to_jiffies(USB_ID_DEBOUNCE_MS);
-	INIT_DELAYED_WORK(&info->wq_detcable, qcom_usb_extcon_detect_cable);
+
+	ret = devm_delayed_work_autocancel(dev, &info->wq_detcable,
+					   qcom_usb_extcon_detect_cable);
+	if (ret)
+		return ret;
 
 	info->irq = platform_get_irq_byname(pdev, "usb_id");
 	if (info->irq < 0)
@@ -105,15 +110,6 @@ static int qcom_usb_extcon_probe(struct platform_device *pdev)
 	return 0;
 }
 
-static int qcom_usb_extcon_remove(struct platform_device *pdev)
-{
-	struct qcom_usb_extcon_info *info = platform_get_drvdata(pdev);
-
-	cancel_delayed_work_sync(&info->wq_detcable);
-
-	return 0;
-}
-
 #ifdef CONFIG_PM_SLEEP
 static int qcom_usb_extcon_suspend(struct device *dev)
 {
@@ -149,7 +145,6 @@ MODULE_DEVICE_TABLE(of, qcom_usb_extcon_dt_match);
 
 static struct platform_driver qcom_usb_extcon_driver = {
 	.probe		= qcom_usb_extcon_probe,
-	.remove		= qcom_usb_extcon_remove,
 	.driver		= {
 		.name	= "extcon-pm8941-misc",
 		.pm	= &qcom_usb_extcon_pm_ops,
-- 
2.25.4


-- 
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =] 

Re: [RFC PATCH v2 2/8] MAINTAINERS: Add entry for devm helpers

[Hans de Goede]

Hi,

On 3/8/21 9:14 AM, Matti Vaittinen wrote:
> Devm helper header containing small inline helpers was added.
> Hans promised to maintain it.

Yes I did promise that, didn't I?  FWIW going this route is still
fine by me, assuming that having someone else maintain this makes
this easier on / more acceptable to Greg.

This is still going to need an Ack from Greg though.

Regards,

Hans



> 
> Add Hans as maintainer and myself as designated reviewer.
> 
> Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
> ---
>  MAINTAINERS | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index d92f85ca831d..ffcb00006e14 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -5169,6 +5169,12 @@ M:	Torben Mathiasen <device@lanana.org>
>  S:	Maintained
>  W:	http://lanana.org/docs/device-list/index.html
>  
> +DEVICE RESOURCE MANAGEMENT HELPERS
> +M:	Hans de Goede <hdegoede@redhat.com>
> +R:	Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
> +S:	Maintained
> +F:	include/linux/devm-helpers.h
> +
>  DEVICE-MAPPER  (LVM)
>  M:	Alasdair Kergon <agk@redhat.com>
>  M:	Mike Snitzer <snitzer@redhat.com>
>