Re: [PATCH 28/30] r/o bind mounts: track numbers of writers to mounts

Dave Hansen
2008-02-20T21:12:51Z

On Mon, 2008-02-18 at 17:10 +0100, Miklos Szeredi wrote:
>
> > + /*
> > + * We don't have to hold all of the locks at the
> > + * same time here because we know that we're the
> > + * last reference to mnt and that no new writers
> > + * can come in.
> > + */
> > + for_each_possible_cpu(cpu) {
> > + struct mnt_writer *cpu_writer = &per_cpu(mnt_writers, cpu);
> > + if (cpu_writer->mnt != mnt)
> > + continue;
> > + spin_lock(&cpu_writer->lock);
> > + atomic_add(cpu_writer->count, &mnt->__mnt_writers);
> > + cpu_writer->count = 0;
>
> I think you should also add a
>
> cpu_writer->mnt = NULL;
>
> here. It's not a bug, but I had to think a bit about why it's not a
> bug.

Yeah, I kinda copied the code from __clear_mnt_count() where keeping
->mnt is actually a mini optimization. But, there is certainly no
chance of that mnt popping up again after a __mntput(), so I clear it in
there now. I also added a comment explaining.

-- Dave