Re: [PATCH v4 06/17] virt: acrn: Introduce VM management interfaces

Greg Kroah-Hartman
2020-09-28T12:25:57Z

On Mon, Sep 28, 2020 at 02:29:34PM +0800, Shuo A Liu wrote:
> On Mon 28.Sep'20 at 7:25:16 +0200, Greg Kroah-Hartman wrote:
> > On Mon, Sep 28, 2020 at 11:50:30AM +0800, Shuo A Liu wrote:
> > > > > + write_lock_bh(&acrn_vm_list_lock);
> > > > > + list_add(&vm->list, &acrn_vm_list);
> > > > > + write_unlock_bh(&acrn_vm_list_lock);
> > > >
> > > > Why are the _bh() variants being used here?
> > > >
> > > > You are only accessing this list from userspace context in this patch.
> > > >
> > > > Heck, you aren't even reading from the list, only writing to it...
> > >
> > > acrn_vm_list is read in a tasklet which dispatch I/O requests and is wrote
> > > in VM creation ioctl. Use the rwlock mechanism to protect it.
> > > The reading operation is introduced in the following patches of this
> > > series. So i keep the lock type at the moment of introduction.
> >
> > Ok, but think about someone trying to review this code. Does this lock
> > actually make sense here? No, it does not. How am I supposed to know
> > to look at future patches to determine that it changes location and
> > usage to require this?
>
> OK. May i know how to handle such kind of code submission? Or which way
> following do you prefer?
> 1) Use a mutex lock here, then change it to rwlock in a later patch
> of this series.

Wouldn't this make more sense if you had to read these one after
another?

> 2) Add more comments in changelog about the lock. (Now, there is
> comment around the acrn_vm_list_lock)

It's hard to verify a comment's statement without digging through other
patches in the series, right? You want the reviewer to just trust you?
:)

Again, what would _YOU_ want to see if you had to review this?

> > That's just not fair, would you want to review something like this?
> >
> > And a HUGE meta-comment, again, why am I the only one reviewing this
> > stuff? Why do you have a ton of Intel people on the Cc: yet it is, once
> > again, my job to do this?
>
> The patchset has been reviewed in Intel's internal mailist several
> rounds and got Reviewed-by: before send out. That's why i Cced many
> Intel people as well.

Then why didn't any of those intel people on the cc: actually review it
after you have sent it out? Why is it only me? Do I need to wait
longer for them to get to this? I'll gladly do so next time...

> This patchset is all about a common driver for the ACRN hypervisor
> support. I put the code in drivers/virt/ and found you are one of the
> maintainer of vboxguest driver which is in the same subdirectory. I
> thought you should be the right person to be Cced when i submitted this
> series.

I am, I'm not complaining about that. I'm complaining that it seems to
be _only_ me reviewing this here, and not any of the people you are cc:ing
from intel. Most of those people should be giving you this same type of
review comments and not forcing an external person to do so, right?

> Certainly, any comments are welcome. And really appreciate your review
> and help. I have little experience to submit a new driver to the
> community, my apologies if thing goes wrong.

You didn't do anything wrong, I'm arguing about the larger meta-issue I
have right now with Intel and the lack of reviews that seems to happen
from other Intel people on their co-workers patches.

Anyway, you are doing fine, it's an iterative process, hopefully you can
also review other people's patches in this area that are being posted as
well.

thanks,

greg k-h