From: Stefano Stabellini <sstabellini@kernel.org>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
xen-devel@lists.xen.org, linux-kernel@vger.kernel.org,
jgross@suse.com, Stefano Stabellini <stefano@aporeto.com>
Subject: Re: [PATCH v3 11/13] xen/pvcalls: implement poll command
Date: Tue, 12 Sep 2017 15:17:41 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.10.1709121502210.9439@sstabellini-ThinkPad-X260> (raw)
In-Reply-To: <6c9613d8-8219-d06f-9095-fa57474ed518@oracle.com>
On Tue, 12 Sep 2017, Boris Ostrovsky wrote:
> >>> +
> >>> +unsigned int pvcalls_front_poll(struct file *file, struct socket *sock,
> >>> + poll_table *wait)
> >>> +{
> >>> + struct pvcalls_bedata *bedata;
> >>> + struct sock_mapping *map;
> >>> +
> >>> + if (!pvcalls_front_dev)
> >>> + return POLLNVAL;
> >>> + bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> >>> +
> >>> + map = (struct sock_mapping *) READ_ONCE(sock->sk->sk_send_head);
> >> I just noticed this --- why is it READ_ONCE? Are you concerned that
> >> sk_send_head may change?
> > No, but I wanted to avoid partial reads. A caller could call
> > pvcalls_front_accept and pvcalls_front_poll on newsock almost at the
> > same time (it is probably not the correct way to use the API), I wanted
> > to make sure that "map" is either read correctly, or not read at all.
>
> How can you have a partial read on a pointer?
I don't think that the compiler makes any promises on translating a
pointer read into a single read instruction. Of couse, I expect gcc to
actually do it without any need for READ/WRITE_ONCE.
next prev parent reply other threads:[~2017-09-12 22:17 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-31 22:57 [PATCH v3 00/13] introduce the Xen PV Calls frontend Stefano Stabellini
2017-07-31 22:57 ` [PATCH v3 01/13] xen/pvcalls: introduce the pvcalls xenbus frontend Stefano Stabellini
2017-07-31 22:57 ` [PATCH v3 02/13] xen/pvcalls: implement frontend disconnect Stefano Stabellini
2017-08-11 22:43 ` Boris Ostrovsky
2017-09-09 0:07 ` Stefano Stabellini
2017-07-31 22:57 ` [PATCH v3 03/13] xen/pvcalls: connect to the backend Stefano Stabellini
2017-08-11 22:55 ` Boris Ostrovsky
2017-09-09 0:14 ` Stefano Stabellini
2017-07-31 22:57 ` [PATCH v3 04/13] xen/pvcalls: implement socket command and handle events Stefano Stabellini
2017-08-13 0:42 ` Boris Ostrovsky
2017-09-08 23:20 ` Stefano Stabellini
2017-07-31 22:57 ` [PATCH v3 05/13] xen/pvcalls: implement connect command Stefano Stabellini
2017-08-13 1:12 ` Boris Ostrovsky
2017-09-08 21:23 ` Stefano Stabellini
2017-07-31 22:57 ` [PATCH v3 06/13] xen/pvcalls: implement bind command Stefano Stabellini
2017-08-13 1:22 ` Boris Ostrovsky
2017-09-08 21:46 ` Stefano Stabellini
2017-07-31 22:57 ` [PATCH v3 07/13] xen/pvcalls: implement listen command Stefano Stabellini
2017-08-13 1:28 ` Boris Ostrovsky
2017-07-31 22:57 ` [PATCH v3 08/13] xen/pvcalls: implement accept command Stefano Stabellini
2017-08-15 2:00 ` Boris Ostrovsky
2017-08-15 2:04 ` Boris Ostrovsky
2017-09-08 21:58 ` Stefano Stabellini
2017-09-08 22:16 ` Stefano Stabellini
2017-07-31 22:57 ` [PATCH v3 09/13] xen/pvcalls: implement sendmsg Stefano Stabellini
2017-08-15 2:31 ` Boris Ostrovsky
2017-09-08 23:48 ` Stefano Stabellini
2017-07-31 22:57 ` [PATCH v3 10/13] xen/pvcalls: implement recvmsg Stefano Stabellini
2017-08-15 2:39 ` Boris Ostrovsky
2017-09-08 23:11 ` Stefano Stabellini
2017-07-31 22:57 ` [PATCH v3 11/13] xen/pvcalls: implement poll command Stefano Stabellini
2017-08-15 20:30 ` Boris Ostrovsky
2017-09-08 23:03 ` Stefano Stabellini
2017-09-12 14:14 ` Boris Ostrovsky
2017-09-12 22:17 ` Stefano Stabellini [this message]
2017-09-12 23:04 ` Boris Ostrovsky
2017-09-12 23:13 ` Stefano Stabellini
2017-09-12 23:18 ` Stefano Stabellini
2017-07-31 22:57 ` [PATCH v3 12/13] xen/pvcalls: implement release command Stefano Stabellini
2017-08-15 20:44 ` Boris Ostrovsky
2017-09-08 23:09 ` Stefano Stabellini
2017-07-31 22:57 ` [PATCH v3 13/13] xen: introduce a Kconfig option to enable the pvcalls frontend Stefano Stabellini
2017-08-11 22:36 ` [PATCH v3 01/13] xen/pvcalls: introduce the pvcalls xenbus frontend Boris Ostrovsky
2017-08-10 15:07 ` [PATCH v3 00/13] introduce the Xen PV Calls frontend Boris Ostrovsky
2017-08-10 18:15 ` Stefano Stabellini
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=alpine.DEB.2.10.1709121502210.9439@sstabellini-ThinkPad-X260 \
--to=sstabellini@kernel.org \
--cc=boris.ostrovsky@oracle.com \
--cc=jgross@suse.com \
--cc=linux-kernel@vger.kernel.org \
--cc=stefano@aporeto.com \
--cc=xen-devel@lists.xen.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 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).