Re: [Xen-devel] [PATCH v12 2/3] x86/mem_sharing: reset a fork

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Thu, Mar 26, 2020 at 8:52 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>
> On 26.03.2020 15:48, Tamas K Lengyel wrote:
> > On Thu, Mar 26, 2020 at 4:17 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
> >>
> >> On 23.03.2020 18:04, Tamas K Lengyel wrote:
> >>> +static int mem_sharing_fork_reset(struct domain *d, struct domain *pd)
> >>> +{
> >>> +    int rc;
> >>> +    struct p2m_domain *p2m = p2m_get_hostp2m(d);
> >>> +    struct page_info *page, *tmp;
> >>> +
> >>> +    spin_lock(&d->page_alloc_lock);
> >>> +    domain_pause(d);
> >>
> >> Why do you take the lock first?
> >
> > No particular reason - does the order matter?
>
> I think you'd better avoid holding a lock for extended periods
> of time. And what's perhaps worse, what if a vCPU of the domain
> sits in Xen trying to acquire this lock - you'd deadlock trying
> to pause the domain then.

OK, I'll invert them order then.

Thanks,
Tamas