linux-kernel - Re: [PATCH 7/7] staging: comedi: comedi_fops: extend spin-lock scope in comedi

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Message-ID: <551BB61D.8090306@mev.co.uk>
Date:	Wed, 01 Apr 2015 10:10:53 +0100
From:	Ian Abbott <abbotti@....co.uk>
To:	Hartley Sweeten <HartleyS@...ionengravers.com>,
	"driverdev-devel@...uxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/7] staging: comedi: comedi_fops: extend spin-lock scope
 in comedi_event()

On 31/03/15 17:13, Hartley Sweeten wrote:
> On Tuesday, March 31, 2015 2:43 AM, Ian Abbott wrote:
>> On 30/03/15 17:47, Hartley Sweeten wrote:
>>> On Friday, March 27, 2015 8:13 AM, Ian Abbott wrote:
>>>> `comedi_event()` is called from low-level drivers to handle comedi
>>>> asynchronous command event flags.  As a safety check, it checks the
>>>> subdevice's "run" flags to make sure an asynchronous command is running.
>>>> It can also change the run flags to mark the command as no longer
>>>> running (possibly also marking it as terminated with an error).
>>>> Checking the runflags and modifying them involves two uses of the
>>>> subdevice's spin-lock.  It seems better to do it with a single use of
>>>> the spin-lock.  This also avoids possible interactions with
>>>> `do_become_nonbusy()`.
>>>>
>>>> Acquire the subdevice's spin-lock at the start of `comedi_event()` and
>>>> release it near the end, before a possible call to `kill_fasync()` (but
>>>> after it's parameter values have been determined).
>>>>
>>>> Add and make use of few new inline helper functions:
>>>>
>>>> * `__comedi_clear_subdevice_runflags()` -- clears some run flags without
>>>>     using the spin-lock
>>>> * `__comedi_set_subdevice_runflags()` -- sets some run flags without
>>>>     using the spin-lock
>>>> * `__comedi_get_subdevice_runflags()` -- a spin-lockless version of
>>>>     `comedi_get_subdevice_runflags()
>>>> * `__comedi_is_subdevice_running()` -- a spin-lockless version of
>>>> * `comedi_is_subdevice_running()`
>>>>
>>>> Signed-off-by: Ian Abbott <abbotti@....co.uk>
>>>
>>> Ian,
>>>
>>> For completeness, the comedi_alloc_spriv() helper should probably use
>>> __comedi_set_subdevice_runflags() to set the COMEDI_SRF_FREE_SPRIV
>>> bit.
>>
>> Good point.  "drivers/staging/comedi/drivers.c" also reads the runflags
>> directly, so perhaps __comedi_clear_subdevice_runflags(),
>> __comedi_set_subdevice_runflags() and __comedi_get_subdevice_runflags()
>> should be placed in "drivers/staging/comedi/comedi_internal.h".  Or we
>> could ditch all three of those inline functions as they are just simple
>> one-liners.
>
> comedi_internal.h works for mw. We just don't want to expose those functions
> to the drivers.

Okay, I'll do that in a separate patch since you've already signed off 
on this one.

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@....co.uk> )=-
-=(                          Web: http://www.mev.co.uk/  )=-
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