linux-kernel - Re: [PATCH v3 2/3] iio: add MEMSensing MSA311 3-axis accelerometer driver

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Message-ID: <20220701130642.pjwucd2cvbr4uq3x@CAB-WSD-L081021.sigma.sbrf.ru>
Date:   Fri, 1 Jul 2022 13:06:17 +0000
From:   Dmitry Rokosov <DDRokosov@...rdevices.ru>
To:     Jonathan Cameron <jic23@...nel.org>
CC:     Andy Shevchenko <andy.shevchenko@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "stano.jakubek@...il.com" <stano.jakubek@...il.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "lars@...afoo.de" <lars@...afoo.de>,
        "stephan@...hold.net" <stephan@...hold.net>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        kernel <kernel@...rdevices.ru>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/3] iio: add MEMSensing MSA311 3-axis accelerometer
 driver

On Sun, Jun 19, 2022 at 01:31:42PM +0100, Jonathan Cameron wrote:
> On Thu, 16 Jun 2022 17:02:08 +0000
> Dmitry Rokosov <DDRokosov@...rdevices.ru> wrote:
> 
> 
> 
> > > > +       err = -EINVAL;
> > > > +       mutex_lock(&msa311->lock);
> > > > +       for (odr = 0; odr < ARRAY_SIZE(msa311_odr_table); ++odr)
> > > > +               if (val == msa311_odr_table[odr].val &&
> > > > +                   val2 == msa311_odr_table[odr].val2) {
> > > > +                       err = msa311_set_odr(msa311, odr);  
> > >   
> > > > +                       if (err) {
> > > > +                               dev_err(dev, "cannot update freq (%d)\n", err);
> > > > +                               goto failed;
> > > > +                       }  
> > > 
> > > Why is this inside the loop and more important under lock? Also you
> > > may cover the initial error code by this message when moving it out of
> > > the loop and lock.
> > > 
> > > Ditto for other code snippets in other function(s) where applicable.
> > >   
> > 
> > Yes, I can move dev_err() outside of loop. But all ODR search loop
> > should be under lock fully, because other msa311 operations should not
> > be executed when we search proper ODR place.
> 
> I don't see why?  The search itself is for a match of the input to const data.
> That can occur before taking the lock to do the actual write.
> 
> I don't see any additional race beyond the one that is always there of
> a thread updating ODR whilst another is accessing the device.  Which order
> those events happen in is not controlled by the driver, but the output
> will be consistent with one or other order of those two accesses.
> 
> Jonathan

Agreed, will be changed in the v4.

-- 
Thank you,
Dmitry