Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 9 Jun 2021 23:16:50 +0900
From:   William Breathitt Gray <vilhelm.gray@gmail.com>
To:     Dan Carpenter <dan.carpenter@oracle.com>
Cc:     jic23@kernel.org, linux-stm32@st-md-mailman.stormreply.com,
        kernel@pengutronix.de, a.fatoum@pengutronix.de,
        kamel.bouhara@bootlin.com, gwendal@chromium.org,
        alexandre.belloni@bootlin.com, david@lechnology.com,
        linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, syednwaris@gmail.com,
        patrick.havelange@essensium.com, fabrice.gasnier@st.com,
        mcoquelin.stm32@gmail.com, alexandre.torgue@st.com,
        o.rempel@pengutronix.de, jarkko.nikula@linux.intel.com
Subject: Re: [PATCH v11 26/33] counter: Add character device interface
Message-ID: <YMDNUrbUDtzaTjwA@shinobu>
References: <cover.1623201081.git.vilhelm.gray@gmail.com>
 <2b9526ab7f2de91bb867cbd3b12552c77c00b655.1623201082.git.vilhelm.gray@gmail.com>
 <20210609080708.GL10983@kadam>
 <YMB7mq0LHqmyAAzb@shinobu>
 <20210609085938.GM10983@kadam>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
        protocol="application/pgp-signature"; boundary="6W+PPeNZqxPVxyi9"
Content-Disposition: inline
In-Reply-To: <20210609085938.GM10983@kadam>
Precedence: bulk


--6W+PPeNZqxPVxyi9
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Wed, Jun 09, 2021 at 11:59:38AM +0300, Dan Carpenter wrote:
> On Wed, Jun 09, 2021 at 05:28:10PM +0900, William Breathitt Gray wrote:
> > On Wed, Jun 09, 2021 at 11:07:08AM +0300, Dan Carpenter wrote:
> > > On Wed, Jun 09, 2021 at 10:31:29AM +0900, William Breathitt Gray wrot=
e:
> > > > +static int counter_set_event_node(struct counter_device *const cou=
nter,
> > > > +				  struct counter_watch *const watch,
> > > > +				  const struct counter_comp_node *const cfg)
> > > > +{
> > > > +	struct counter_event_node *event_node;
> > > > +	struct counter_comp_node *comp_node;
> > > > +
> > >=20
> > > The caller should be holding the counter->events_list_lock lock but i=
t's
> > > not.
> >=20
> > Hi Dan,
> >=20
> > The counter_set_event_node() function doesn't access or modify
> > counter->events_list (it works on counter->next_events_list) so holding
> > the counter->events_list_lock here isn't necessary.
> >=20
>=20
> There needs to be some sort of locking or this function can race with
> itself.  (Two threads add the same event at exactly the same time).  It
> looks like it can also race with counter_disable_events() leading to a
> use after free.

All right, I'll add in a lock to protect this function so it doesn't
race with itself nor counter_disable_events().

> > > > +	/* Search for event in the list */
> > > > +	list_for_each_entry(event_node, &counter->next_events_list, l)
> > > > +		if (event_node->event =3D=3D watch->event &&
> > > > +		    event_node->channel =3D=3D watch->channel)
> > > > +			break;
> > > > +
> > > > +	/* If event is not already in the list */
> > > > +	if (&event_node->l =3D=3D &counter->next_events_list) {
> > > > +		/* Allocate new event node */
> > > > +		event_node =3D kmalloc(sizeof(*event_node), GFP_ATOMIC);
>=20
> Btw, say we decided that we can add/remove events locklessly, then these
> GFP_ATOMICs can be changed to GFP_KERNEL.

Because I'll be using a lock I'll keep these as GFP_ATOMICs afterall.

Thanks,

William Breathitt Gray

--6W+PPeNZqxPVxyi9
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
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=d68x
-----END PGP SIGNATURE-----

--6W+PPeNZqxPVxyi9--