From: Paolo Bonzini <pbonzini@redhat.com>
To: liu ping fan <qemulist@gmail.com>
Cc: Peter Maydell <peter.maydell@linaro.org>,
Anthony Liguori <anthony@codemonkey.ws>,
"Michael S. Tsirkin" <mst@redhat.com>,
Jan Kiszka <jan.kiszka@siemens.com>,
qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: [Qemu-devel] [RFC PATCH 2/2] mem: prepare address_space listener rcu style
Date: Wed, 15 May 2013 05:19:48 -0400 (EDT) [thread overview]
Message-ID: <154112326.1807249.1368609588959.JavaMail.root@redhat.com> (raw)
In-Reply-To: <CAJnKYQnXjR5+pE3hVijCevHVCX0nYunibMwTZ4xgDVNLr+tYcw@mail.gmail.com>
> > > rcu_read_lock();
> > > map = rcu_dereference(d->cur_map)
> > > if (unlikely(d->prev_map!=map) {
> > > d->root = map->root;
> > > d->pgtbl = map->pgtbl;
> > > }
> > > ......
> > > rcu_read_unlock();
> > >
> > > Then it can avoid ABA problem.
> >
> > I don't see the assignment of prev_map, which is where the ABA problem
> > arises.
If you do this:
> rcu_read_lock();
> map = rcu_derefenrence(d->cur_map)
> if (unlikely(d->prev_map!=map) {
> d->root = map->root;
> d->pgtbl = map->pgtbl;
> d->prev_map = map;
> }
> ....
> rcu_read_unlock();
It can happen. The problem is that prev_map can change _after_
the rcu_read_unlock. It is the same as your previous solution.
Please just use the load-and-check idiom. I'll post my RCU
implementation as soon as I finish the documentation.
Paolo
next prev parent reply other threads:[~2013-05-15 9:19 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-13 3:21 [Qemu-devel] [RFC PATCH 0/2] make memory listener prepared for rcu style Liu Ping Fan
2013-05-13 3:21 ` [Qemu-devel] [RFC PATCH 1/2] mem: make phys_section and phys_map_nodes prepared for RCU Liu Ping Fan
2013-05-13 9:20 ` Paolo Bonzini
2013-05-14 3:38 ` liu ping fan
2013-05-14 9:27 ` Paolo Bonzini
2013-05-15 7:04 ` liu ping fan
2013-05-26 13:02 ` liu ping fan
2013-05-27 11:54 ` Paolo Bonzini
2013-05-29 1:52 ` liu ping fan
2013-05-13 3:21 ` [Qemu-devel] [RFC PATCH 2/2] mem: prepare address_space listener rcu style Liu Ping Fan
2013-05-13 9:31 ` Paolo Bonzini
2013-05-14 5:47 ` liu ping fan
2013-05-14 9:34 ` Paolo Bonzini
2013-05-15 1:29 ` liu ping fan
2013-05-15 8:22 ` Paolo Bonzini
2013-05-15 9:11 ` liu ping fan
2013-05-15 9:19 ` Paolo Bonzini [this message]
2013-05-16 9:09 ` Paolo Bonzini
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=154112326.1807249.1368609588959.JavaMail.root@redhat.com \
--to=pbonzini@redhat.com \
--cc=anthony@codemonkey.ws \
--cc=jan.kiszka@siemens.com \
--cc=mst@redhat.com \
--cc=peter.maydell@linaro.org \
--cc=qemu-devel@nongnu.org \
--cc=qemulist@gmail.com \
--cc=stefanha@redhat.com \
/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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).