Re: [Xen-devel] [PATCH 1/2] smp: convert the cpu maps lock into a rw lock

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Feb 19, 2020 at 01:56:02PM +0100, Jan Beulich wrote:
> On 13.02.2020 12:32, Roger Pau Monne wrote:
> >  void __init register_cpu_notifier(struct notifier_block *nb)
> >  {
> > -    if ( !spin_trylock(&cpu_add_remove_lock) )
> > +    if ( !write_trylock(&cpu_add_remove_lock) )
> >          BUG(); /* Should never fail as we are called only during boot. */
> >      notifier_chain_register(&cpu_chain, nb);
> > -    spin_unlock(&cpu_add_remove_lock);
> > +    write_unlock(&cpu_add_remove_lock);
> >  }
> 
> So why a write lock here?

notifier_chain_register calls cannot be made in parallel, as they
modify the underlying notifier list without taking any additional
locks.

Thanks, Roger.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel