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From: Tamas K Lengyel <tamas@tklengyel.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: "Julien Grall" <julien@xen.org>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Tamas K Lengyel" <tamas.lengyel@intel.com>,
	"Wei Liu" <wl@xen.org>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Ian Jackson" <ian.jackson@eu.citrix.com>,
	"George Dunlap" <george.dunlap@citrix.com>,
	Xen-devel <xen-devel@lists.xenproject.org>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH v12 2/3] x86/mem_sharing: reset a fork
Date: Thu, 26 Mar 2020 17:40:55 -0600
Message-ID: <CABfawhkyK4UBhHZx=MZ-EQaUrVC2WsCkG6=Yj-=+uqd9uLJZ0A@mail.gmail.com> (raw)
In-Reply-To: <CABfawhkoEt1wZ9hT2Tra8Mw0jkXtNzTXt+Znf1WuTYf-nnDd+g@mail.gmail.com>

On Thu, Mar 26, 2020 at 8:53 AM Tamas K Lengyel <tamas@tklengyel.com> wrote:
>
> On Thu, Mar 26, 2020 at 8:52 AM Jan Beulich <jbeulich@suse.com> wrote:
> >
> > On 26.03.2020 15:48, Tamas K Lengyel wrote:
> > > On Thu, Mar 26, 2020 at 4:17 AM Jan Beulich <jbeulich@suse.com> 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.

It turns out we also need to take the recursive lock here since we'll
free the pages. Fixed now and everything works as expected.

Tamas


  reply index

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-23 17:04 [Xen-devel] [PATCH v12 0/3] VM forking Tamas K Lengyel
2020-03-23 17:04 ` [Xen-devel] [PATCH v12 1/3] xen/mem_sharing: " Tamas K Lengyel
2020-03-25 15:47   ` Roger Pau Monné
2020-03-25 16:04     ` Tamas K Lengyel
2020-03-25 16:16     ` Tamas K Lengyel
2020-03-25 16:34     ` Tamas K Lengyel
2020-03-25 16:42       ` Julien Grall
2020-03-25 16:47         ` Tamas K Lengyel
2020-03-25 16:51           ` Julien Grall
2020-03-25 17:00             ` Tamas K Lengyel
2020-03-25 17:16               ` Roger Pau Monné
2020-03-25 17:47                 ` Tamas K Lengyel
2020-03-25 16:54         ` Roger Pau Monné
2020-03-26  7:02           ` Jan Beulich
2020-03-26  8:42             ` Roger Pau Monné
2020-03-26  7:07     ` Jan Beulich
2020-03-26  9:10       ` Roger Pau Monné
2020-03-26 17:01         ` Tamas K Lengyel
2020-03-26 12:33   ` Jan Beulich
2020-03-26 14:52     ` Tamas K Lengyel
2020-03-23 17:04 ` [Xen-devel] [PATCH v12 2/3] x86/mem_sharing: reset a fork Tamas K Lengyel
2020-03-25 15:52   ` Roger Pau Monné
2020-03-25 15:54     ` Tamas K Lengyel
2020-03-26 10:16   ` Jan Beulich
2020-03-26 14:48     ` Tamas K Lengyel
2020-03-26 14:52       ` Jan Beulich
2020-03-26 14:53         ` Tamas K Lengyel
2020-03-26 23:40           ` Tamas K Lengyel [this message]
2020-03-23 17:04 ` [Xen-devel] [PATCH v12 3/3] xen/tools: VM forking toolstack side Tamas K Lengyel

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