On Fri, Oct 11, 2019 at 01:33:03PM -0700, Dmitry Torokhov wrote: > On Fri, Oct 11, 2019 at 09:25:52PM +0200, Benjamin Tissoires wrote: > > On Fri, Oct 11, 2019 at 8:26 PM Dmitry Torokhov > > <dmitry.torok...@gmail.com> wrote: > > > > > > On Fri, Oct 11, 2019 at 04:52:04PM +0200, Benjamin Tissoires wrote: > > > > Hi Andrey, > > > > > > > > On Mon, Oct 7, 2019 at 7:13 AM Andrey Smirnov > > > > <andrew.smir...@gmail.com> wrote: > > > > > > > > > > To simplify resource management in commit that follows as well as to > > > > > save a couple of extra kfree()s and simplify hidpp_ff_deinit() switch > > > > > driver code to use devres to manage the life-cycle of FF private data. > > > > > > > > > > Signed-off-by: Andrey Smirnov <andrew.smir...@gmail.com> > > > > > Cc: Jiri Kosina <ji...@kernel.org> > > > > > Cc: Benjamin Tissoires <benjamin.tissoi...@redhat.com> > > > > > Cc: Henrik Rydberg <rydb...@bitmath.org> > > > > > Cc: Sam Bazely <sambaz...@fastmail.com> > > > > > Cc: Pierre-Loup A. Griffais <pgriff...@valvesoftware.com> > > > > > Cc: Austin Palmer <aust...@valvesoftware.com> > > > > > Cc: linux-in...@vger.kernel.org > > > > > Cc: linux-kernel@vger.kernel.org > > > > > Cc: sta...@vger.kernel.org > > > > > > > > This patch doesn't seem to fix any error, is there a reason to send it > > > > to stable? (besides as a dependency of the rest of the series). > > > > > > > > > --- > > > > > drivers/hid/hid-logitech-hidpp.c | 53 > > > > > +++++++++++++++++--------------- > > > > > 1 file changed, 29 insertions(+), 24 deletions(-) > > > > > > > > > > diff --git a/drivers/hid/hid-logitech-hidpp.c > > > > > b/drivers/hid/hid-logitech-hidpp.c > > > > > index 0179f7ed77e5..58eb928224e5 100644 > > > > > --- a/drivers/hid/hid-logitech-hidpp.c > > > > > +++ b/drivers/hid/hid-logitech-hidpp.c > > > > > @@ -2079,6 +2079,11 @@ static void hidpp_ff_destroy(struct ff_device > > > > > *ff) > > > > > struct hidpp_ff_private_data *data = ff->private; > > > > > > > > > > kfree(data->effect_ids); > > > > > > > > Is there any reasons we can not also devm alloc data->effect_ids? > > > > > > > > > + /* > > > > > + * Set private to NULL to prevent input_ff_destroy() from > > > > > + * freeing our devres allocated memory > > > > > > > > Ouch. There is something wrong here: input_ff_destroy() calls > > > > kfree(ff->private), when the data has not been allocated by > > > > input_ff_create(). This seems to lack a little bit of symmetry. > > > > > > Yeah, ff and ff-memless essentially take over the private data assigned > > > to them. They were done before devm and the lifetime of the "private" > > > data pieces was tied to the lifetime of the input device to simplify > > > error handling and teardown. > > > > Yeah, that stealing of the pointer is not good :) > > But OTOH, it helps > > > > > > > > Maybe we should clean it up a bit... I'm open to suggestions. > > > > The problem I had when doing the review was that there is no easy way > > to have a "devm_input_ff_create_()", because the way it's built is > > already "devres-compatible": the destroy gets called by input core. > > I do not think we want devm_input_ff_create() explicitly, I think the > fact that you can "build up" an input device by allocating it, then > adding slots, poller, ff support, etc, and input core cleans it up is > all good. It is just the ownership if the driver-private data block is > not very obvious and is not compatible with allocating via devm. > > > > > So I don't have a good answer to simplify in a transparent manner > > without breaking the API. > > > > > > > > In this case maybe best way is to get rid of hidpp_ff_destroy() and not > > > set ff->private and rely on devm to free the buffers. One can get to > > > device private data from ff methods via input_get_drvdata() since they > > > all (except destroy) are passed input device pointer. > > > > Sounds like a good idea. However, it seems there might be a race when > > removing the workqueue: > > the workqueue gets deleted in hidpp_remove, when the input node will > > be freed by devres, so after the call of hidpp_remove. > > Yeah, well, that is a common issue with mixing devm and normal resources > (and workqueue here is that "normal" resource), and we should either: > > - not use devm > - use devm_add_action_or_reset() to work in custom actions that work > freeing of non-managed resources into devm flow.
Actually, there is a door #3: use system workqueue. After all the work that Tejun done on workqueues it is very rare that one actually needs a dedicated workqueue (as works usually execute on one if the system worker threads that are shared with other workqueues anyway). -- Dmitry
