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

[Ian Abbott]

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@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

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.

--
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@xxxxxxxxx> )=-
-=(                          Web: http://www.mev.co.uk/  )=-
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/