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

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Date:	Mon, 30 Mar 2015 16:47:27 +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 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.

Regards,
Hartley

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