From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: xen-devel@lists.xenproject.org, Julien Grall <julien@xen.org>,
Wei Liu <wl@xen.org>, Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [Xen-devel] [PATCH 0/3] x86: fixes/improvements for scratch cpumask
Date: Thu, 13 Feb 2020 11:05:03 +0100 [thread overview]
Message-ID: <20200213100503.GW4679@Air-de-Roger> (raw)
In-Reply-To: <c09e9d06-af6b-014e-9d0c-027cdfe753d4@suse.com>
On Thu, Feb 13, 2020 at 10:53:43AM +0100, Jan Beulich wrote:
> On 12.02.2020 22:05, Julien Grall wrote:
> > On 12/02/2020 17:49, Roger Pau Monne wrote:
> >> Commit:
> >>
> >> 5500d265a2a8fa63d60c08beb549de8ec82ff7a5
> >> x86/smp: use APIC ALLBUT destination shorthand when possible
> >
> > There is a more subtle problem introduced by this patch. I thought I
> > would mention it here just in case this affect the approach you have
> > chosen in this series.
> >
> > get_cpu_maps() is used by stop_machine_run() to serialize the callers.
> > If the latter fails to acquire the lock, it will bail out.
> > Unfortunately, rcu_barrier() is implemented using stop_machine_run() and
> > will be turned to pretty much a NOP if the latter fails (e.g the lock
> > cannot be acquired).
> >
> > This means that the rcu_barrier() will not do the expected job and
> > potentially introduce unknown issues (e.g use-after-free...).
> >
> > Before your patch, it would have been pretty hard to hit the problem
> > above. After, you can race more easily with rcu_barrier() as sending IPI
> > is pretty common.
> >
> > Sadly, I don't have a suggestion yet how to fix this problem.
>
> A frequent use like on the IPI sending path suggests the lock may
> want to become an r/w one, where both parties you mention want to
> acquire it in read mode.
I'm already preparing a patch in this direction.
Roger.
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
prev parent reply other threads:[~2020-02-13 10:05 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-12 16:49 [Xen-devel] [PATCH 0/3] x86: fixes/improvements for scratch cpumask Roger Pau Monne
2020-02-12 16:49 ` [Xen-devel] [PATCH 1/3] x86/smp: unify header includes in smp.h Roger Pau Monne
2020-02-12 23:05 ` Wei Liu
2020-02-13 9:54 ` Jan Beulich
2020-02-12 16:49 ` [Xen-devel] [PATCH 2/3] x86/smp: use a dedicated scratch cpumask in send_IPI_mask Roger Pau Monne
2020-02-13 9:59 ` Jan Beulich
2020-02-13 10:03 ` Roger Pau Monné
2020-02-13 10:19 ` Jan Beulich
2020-02-13 11:41 ` Roger Pau Monné
2020-02-13 13:35 ` Jan Beulich
2020-02-12 16:49 ` [Xen-devel] [PATCH 3/3] x86: add accessors for scratch cpu mask Roger Pau Monne
2020-02-13 10:12 ` Jan Beulich
2020-02-13 15:15 ` Roger Pau Monné
2020-02-13 15:43 ` Jan Beulich
2020-02-12 16:53 ` [Xen-devel] [PATCH 0/3] x86: fixes/improvements for scratch cpumask Sander Eikelenboom
2020-02-12 17:01 ` Roger Pau Monné
2020-02-12 17:13 ` Sander Eikelenboom
2020-02-13 9:31 ` Sander Eikelenboom
2020-02-12 21:05 ` Julien Grall
2020-02-13 9:53 ` Jan Beulich
2020-02-13 10:05 ` Roger Pau Monné [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200213100503.GW4679@Air-de-Roger \
--to=roger.pau@citrix.com \
--cc=andrew.cooper3@citrix.com \
--cc=jbeulich@suse.com \
--cc=julien@xen.org \
--cc=wl@xen.org \
--cc=xen-devel@lists.xenproject.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.