linux-kernel - Re: [PATCH RESEND v2 0/5] Add devm helper for work-queue initialization

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Date:   Thu, 10 Jun 2021 10:02:15 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Hans de Goede <hdegoede@...hat.com>,
        Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Matti Vaittinen <mazziesaccount@...il.com>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND v2 0/5] Add devm helper for work-queue
 initialization

Hi Hans, 

On 6/10/21 12:23 AM, Hans de Goede wrote:
> Hi All,
> 
> On 6/8/21 12:09 PM, Matti Vaittinen wrote:
>> This series adds new devm_work_autocancel() helper.
>>
>> Note:
>> "The beef" of this series is the new devm-helper. This means that
>> normally it would be picked-up by Hans. In this case Hans asked if this
>> series could be taken in extconn tree:
>> https://lore.kernel.org/lkml/fbbfba71-bdcc-b78f-48be-d7c657adce61@redhat.com/
> 
> Yes, and given that most of the changes are in the extcon code I still
> believe this is best.
> 
> Alternatively I can create an immutable branch with these 5 patches on
> top of 5.13-rc1 and then send a pull-req to Chanwoo and MyongJoo.

Right. After creating the immutable branch, please send pull-request to me.
I'll merge them. Thanks.

> 
> Chanwoo and/or MyongJoo can you please let us know how you want to proceed
> with this series?
> 
> Regards,
> 
> Hans
> 
> 
> 
>>
>> Many drivers which use work-queues must ensure the work is not queued when
>> driver is detached. Often this is done by ensuring new work is not added and
>> then calling cancel_work_sync() at remove(). In many cases this also requires
>> cleanup at probe error path - which is easy to forget (or get wrong).
>>
>> Also the "by ensuring new work is not added" has a gotcha.
>>
>> It is not strange to see devm managed IRQs scheduling work.
>> Mixing this with manual 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 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.
>>
>> Changelog v2:
>>   - rebased on v5.13-rc2
>>   - split the extcon-max8997 change into two. First a simple,
>>     back-portable fix for omitting IRQ freeing at error path, second
>>     being the devm-simpification which does not need backporting.
>>
>> ---
>>
>> Matti Vaittinen (5):
>>   devm-helpers: Add resource managed version of work init
>>   extcon: extcon-max14577: Fix potential work-queue cancellation race
>>   extcon: extcon-max77693.c: Fix potential work-queue cancellation race
>>   extcon: extcon-max8997: Fix IRQ freeing at error path
>>   extcon: extcon-max8997: Simplify driver using devm
>>
>>  drivers/extcon/extcon-max14577.c | 16 ++++--------
>>  drivers/extcon/extcon-max77693.c | 17 ++++--------
>>  drivers/extcon/extcon-max8997.c  | 45 +++++++++++---------------------
>>  include/linux/devm-helpers.h     | 25 ++++++++++++++++++
>>  4 files changed, 50 insertions(+), 53 deletions(-)
>>
>>
>> base-commit: d07f6ca923ea0927a1024dfccafc5b53b61cfecc
>>
> 
> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics