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

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Date:	Tue, 31 Mar 2015 16:13:02 +0000
From:	Hartley Sweeten <HartleyS@...ionengravers.com>
To:	Ian Abbott <abbotti@....co.uk>,
	"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 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.

Regards,
Hartley

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