Re: [PATCH v7] i2c: virtio: add a virtio i2c frontend driver

[Jie Deng]

On 2021/3/12 16:11, Viresh Kumar wrote:
> On 12-03-21, 15:51, Jie Deng wrote:
> > On 2021/3/12 14:10, Viresh Kumar wrote:
> > > I saw your email about wrong version being sent, I already wrote some
> > > reviews. Sending them anyway for FWIW :)
> > >
> > > On 12-03-21, 21:33, Jie Deng wrote:
> > > > +struct virtio_i2c {
> > > > +	struct virtio_device *vdev;
> > > > +	struct completion completion;
> > > > +	struct i2c_adapter adap;
> > > > +	struct mutex lock;
> > > As I said in the previous version (Yes, we were both waiting for
> > > Wolfram to answer that), this lock shouldn't be required at all.
> > >
> > > And since none of us have a use-case at hand where we will have a
> > > problem without this lock, we should really skip it. We can always
> > > come back and add it if we find an issue somewhere. Until then, better
> > > to keep it simple.
> > The problem is you can't guarantee that adap->algo->master_xfer
> > is only called from i2c_transfer. Any function who holds the adapter can
> > call
> > adap->algo->master_xfer directly.
> See my last reply here, (almost) no one in the mainline kernel call it
> directly. And perhaps you can consider the caller broken in that case
> and so there is no need of an extra lock, unless you have a case that
> is broken.
>
> https://lore.kernel.org/lkml/20210305072903.wtw645rukmqr5hx5@vireshk-i7/
>
> > I prefer to avoid potential issues rather
> > than
> > find a issue then fix.
> This is a very hypothetical issue IMHO as the kernel code doesn't have
> such a user. There is no need of locks here, else the i2c core won't
> have handled it by itself.

I'd like to see Wolfram's opinion.
Is it safe to remove lock in adap->algo->master_xfer ?