Stable Archive on lore.kernel.org
 help / color / Atom feed
From: Benjamin Tissoires <benjamin.tissoires@redhat.com>
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Andrey Smirnov <andrew.smirnov@gmail.com>,
	"open list:HID CORE LAYER" <linux-input@vger.kernel.org>,
	Jiri Kosina <jikos@kernel.org>,
	Henrik Rydberg <rydberg@bitmath.org>,
	Sam Bazely <sambazley@fastmail.com>,
	"Pierre-Loup A . Griffais" <pgriffais@valvesoftware.com>,
	Austin Palmer <austinp@valvesoftware.com>,
	lkml <linux-kernel@vger.kernel.org>,
	"3.8+" <stable@vger.kernel.org>
Subject: Re: [PATCH 1/3] HID: logitech-hidpp: use devres to manage FF private data
Date: Sat, 12 Oct 2019 00:34:30 +0200
Message-ID: <CAO-hwJJjiMdKMGoAEyxXN0+Kc0mBPC_KZn-YoHBx8gWfD=RM3g@mail.gmail.com> (raw)
In-Reply-To: <20191011203303.GF229325@dtor-ws>

On Fri, Oct 11, 2019 at 10:33 PM Dmitry Torokhov
<dmitry.torokhov@gmail.com> 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.torokhov@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.smirnov@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.smirnov@gmail.com>
> > > > > Cc: Jiri Kosina <jikos@kernel.org>
> > > > > Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
> > > > > Cc: Henrik Rydberg <rydberg@bitmath.org>
> > > > > Cc: Sam Bazely <sambazley@fastmail.com>
> > > > > Cc: Pierre-Loup A. Griffais <pgriffais@valvesoftware.com>
> > > > > Cc: Austin Palmer <austinp@valvesoftware.com>
> > > > > Cc: linux-input@vger.kernel.org
> > > > > Cc: linux-kernel@vger.kernel.org
> > > > > Cc: stable@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.

Yep, that's what I meant: input_ff_create() already handles its
cleanup, so there is no point in devm_input_ff_create() as the input
core should clean it up for us.

Cheers,
Benjamin

>
> >
> > 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.
>
> Thanks.
>
> --
> Dmitry


  parent reply index

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-07  5:12 [PATCH 0/3] Logitech G920 fixes Andrey Smirnov
2019-10-07  5:12 ` [PATCH 1/3] HID: logitech-hidpp: use devres to manage FF private data Andrey Smirnov
2019-10-11 14:52   ` Benjamin Tissoires
2019-10-11 18:18     ` Andrey Smirnov
2019-10-11 19:16       ` Benjamin Tissoires
2019-10-11 18:26     ` Dmitry Torokhov
2019-10-11 19:25       ` Benjamin Tissoires
2019-10-11 20:33         ` Dmitry Torokhov
2019-10-11 20:35           ` Dmitry Torokhov
2019-10-11 21:33             ` Dmitry Torokhov
2019-10-11 22:48               ` Benjamin Tissoires
2019-10-11 23:23                 ` Dmitry Torokhov
2019-10-14  9:13                   ` Benjamin Tissoires
2019-10-11 21:02           ` Andrey Smirnov
2019-10-11 21:11             ` Dmitry Torokhov
2019-10-11 22:34           ` Benjamin Tissoires [this message]
2019-10-11 20:52         ` Andrey Smirnov
     [not found]   ` <20191014035417.4CE8F2083B@mail.kernel.org>
2019-10-15  4:45     ` Andrey Smirnov
2019-10-07  5:12 ` [PATCH 2/3] HID: logitech-hidpp: split g920_get_config() Andrey Smirnov
2019-10-07  5:12 ` [PATCH 3/3] HID: logitech-hidpp: add G920 device validation quirk Andrey Smirnov
2019-10-11 14:55   ` Benjamin Tissoires
2019-10-11 19:38     ` Andrey Smirnov
2019-10-11 22:32       ` Benjamin Tissoires
2019-10-11 23:32         ` Andrey Smirnov
2019-10-14  9:47           ` Benjamin Tissoires
2019-10-10 22:38 ` [PATCH 0/3] Logitech G920 fixes Sam Bazley
2019-10-11 14:53 ` Benjamin Tissoires
2019-10-11 18:19   ` Andrey Smirnov

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAO-hwJJjiMdKMGoAEyxXN0+Kc0mBPC_KZn-YoHBx8gWfD=RM3g@mail.gmail.com' \
    --to=benjamin.tissoires@redhat.com \
    --cc=andrew.smirnov@gmail.com \
    --cc=austinp@valvesoftware.com \
    --cc=dmitry.torokhov@gmail.com \
    --cc=jikos@kernel.org \
    --cc=linux-input@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=pgriffais@valvesoftware.com \
    --cc=rydberg@bitmath.org \
    --cc=sambazley@fastmail.com \
    --cc=stable@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Stable Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/stable/0 stable/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 stable stable/ https://lore.kernel.org/stable \
		stable@vger.kernel.org stable@archiver.kernel.org
	public-inbox-index stable

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.stable


AGPL code for this site: git clone https://public-inbox.org/ public-inbox