Re: [PATCH v3] pinmux: Use sequential access to access desc->pinmux data

From: Mukesh Ojha
Date: Mon Oct 28 2024 - 03:01:34 EST


On Wed, Oct 23, 2024 at 12:00:48PM +0200, Linus Walleij wrote:
> Hi Mukesh,
>
> On Mon, Oct 14, 2024 at 9:29 PM Mukesh Ojha <quic_mojha@xxxxxxxxxxx> wrote:
>
> > When two client of the same gpio call pinctrl_select_state() for the
> > same functionality, we are seeing NULL pointer issue while accessing
> > desc->mux_owner.
> >
> > Let's say two processes A, B executing in pin_request() for the same pin
> > and process A updates the desc->mux_usecount but not yet updated the
> > desc->mux_owner while process B see the desc->mux_usecount which got
> > updated by A path and further executes strcmp and while accessing
> > desc->mux_owner it crashes with NULL pointer.
> >
> > Serialize the access to mux related setting with a mutex lock.
> >
> > cpu0 (process A) cpu1(process B)
> >
> > pinctrl_select_state() { pinctrl_select_state() {
> > pin_request() { pin_request() {
> > ...
> > ....
> > } else {
> > desc->mux_usecount++;
> > desc->mux_usecount && strcmp(desc->mux_owner, owner)) {
> >
> > if (desc->mux_usecount > 1)
> > return 0;
> > desc->mux_owner = owner;
> >
> > } }
> >
> > Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
>
> Sorry for taking so long!
>
> I was turning the patch over in my head for the fear that something will
> regress but I can only conclude that we need to test this in-tree, so
> patch applied so we can get some rotation and boot tests in linux-next!

Thanks for queuing.

How to check if this has passed the criteria and not regressing anything ?
Sorry, I have not subscribed to linux-next mailing list to get
regular update.

-Mukesh

>
> Yours,
> Linus Walleij