RE: [PATCH 7/7] staging: comedi: comedi_fops: extend spin-lock scope in comedi_event()

[Hartley Sweeten]

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@xxxxxxxxx>

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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