Re: [PATCH 2/2] hwmon: (dell-smm) Unify i8k_ioctl() and i8k_ioctl_unlocked()

[Guenter Roeck]

On 11/22/21 11:10 AM, Pali Rohár wrote:
> On Monday 22 November 2021 19:50:14 Armin Wolf wrote:
> > Am 22.11.21 um 18:55 schrieb Guenter Roeck:
> > > On 11/22/21 8:01 AM, Pali Rohár wrote:
> > > > On Saturday 20 November 2021 18:03:19 Armin Wolf wrote:
> > > > > The only purpose of i8k_ioctl() is to call i8k_ioctl_unlocked()
> > > > > with i8k_mutex held. Judging from the hwmon code, this mutex
> > > > > only needs to be held when setting the fan speed/mode.
> > > >
> > > > Really? I think that there is no difference between setting and getting
> > > > fan speed/mode. At least I do not see why 'set' needs mutex and 'get' do
> > > > not need it. Some more explanation is needed...
> > > I8K_SET_FAN sets the fan speed and returns the current status. Without
> > > locking, the returned status may not match or be associated with the
> > > previous
> > > set operation.
> > >
> > > Maybe that doesn't matter, and the synchronization is not needed. If so,
> > > you can probably remove the locking entirely.
> > >
> > > Guenter
> >
> > That is the reason i kept the locking code. Since i do not want to break
> > the ioctl interfacein any way, removing the locking code seems too risky
> > to me.
>
> I see. That is a good point.
>
> But there is same race condition also when at the same time going to
> change speed via ioctl and also via hwmon sysfs.

I thought the sysfs code does not change the fan speed and report the
fan status in the same request. Did I miss something ?

Guenter