linux-kernel - Re: [PATCH] driver core: add wait event for deferred probe

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Message-ID: <CAD6h2NTJ1DdJ4j=UxNqgYQ5T16OAJ1saK9BEaMo_5NduG4c_ng@mail.gmail.com>
Date:	Fri, 15 Feb 2013 00:58:23 +0800
From:	Haojian Zhuang <haojian.zhuang@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	viro@...iv.linux.org.uk, Rusty Russell <rusty@...tcorp.com.au>,
	hpa@...ux.intel.com, Jim Cromie <jim.cromie@...il.com>,
	linux-kernel@...r.kernel.org,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Linus Walleij <linus.walleij@...aro.org>,
	broonie@...nsource.wolfsonmicro.com,
	Patch Tracking <patches@...aro.org>
Subject: Re: [PATCH] driver core: add wait event for deferred probe

On 15 February 2013 00:50, Arnd Bergmann <arnd@...db.de> wrote:
> On Thursday 14 February 2013, Haojian Zhuang wrote:
>> On 14 February 2013 23:57, Arnd Bergmann <arnd@...db.de> wrote:
>> > On Thursday 14 February 2013, Haojian Zhuang wrote:
>> >> If you can change it into code in below, it could work. Otherwise, it
>> >> always fails.
>> >>         driver_deferred_probe_enable = true;
>> >>         driver_deferred_probe_trigger();
>> >> +      deferred_probe_work_func(NULL);
>> >>         return 0;
>> >>
>> >> Because deferred_probe_work_func() depends on that deferred_probe is added
>> >> into deferred_probe_active_list. If driver_deferred_probe_trigger() isn't called
>> >> first, the deferred uart probe can't be added into active list. So even you call
>> >> work_func at here, it doesn't help.
>> >>
>> >
>> > Would that not cause two instances of the work function to run at the same time?
>> > That sounds like a source for a lot of problems.
>> >
>> >         Arnd
>>
>> Two instances of the work function? I'm sorry that I don't
>> understanding your meaning.
>> Could you help explain your question?
>
> I mean you end up calling the work function directly, while it gets run as part
> of the work queue on a different CPU at the same time. I just noticed that
> there is actually locking in place in deferred_probe_work_func that prevents
> any actual bugs, but you are still adding extra overhead here.
>
> Maybe just add
>
>         flush_workqueue(deferred_wq);
>
> here?
>
>         Arnd

It's fine to me. Since both of them are flushing workqueue.

Tested-by: <haojian.zhuang@...aro.org>
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