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

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Message-ID: <Zx82vLyD1JMv4Cx6@hu-mojha-hyd.qualcomm.com>
Date: Mon, 28 Oct 2024 12:31:16 +0530
From: Mukesh Ojha <quic_mojha@...cinc.com>
To: Linus Walleij <linus.walleij@...aro.org>
CC: <linux-gpio@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] pinmux: Use sequential access to access desc->pinmux
 data

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@...cinc.com> 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@...cinc.com>
> 
> 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