From: Christoph Hellwig <hch@lst.de>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>, Avi Kivity <avi@scylladb.com>,
linux-aio@kvack.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/4] aio: add a iocb refcount
Date: Thu, 2 Aug 2018 10:59:38 +0200 [thread overview]
Message-ID: <20180802085938.GA13473@lst.de> (raw)
In-Reply-To: <20180801231956.GS30522@ZenIV.linux.org.uk>
On Thu, Aug 02, 2018 at 12:19:56AM +0100, Al Viro wrote:
> On Mon, Jul 30, 2018 at 09:15:42AM +0200, Christoph Hellwig wrote:
> > This is needed to prevent races caused by the way the ->poll API works.
> > To avoid introducing overhead for other users of the iocbs we initialize
> > it to zero and only do refcount operations if it is non-zero in the
> > completion path.
>
> refcount_t looks like a bad match - you, AFAICS, have count 0 for everything
> except poll, while for poll you start with 2. That looks like
> if (iocb->shared && test_and_clear_bit(0, &iocb->shared))
> return;
> kill the sucker
> in your iocb_put() and initializing it to 1 in poll. No?
For non-poll we don't need the recount, so we can ignore that.
For poll we have two reference - submitting and wakee context. We
could replace the refcount_t with an atomic bitops - but it would
a) make the code harder to read than plain old refcounting
b) make the iocb bigger - at least for now as there is nothing
else we can share that unsigned long with.
Your call - I can respin it either way.
next prev parent reply other threads:[~2018-08-02 10:45 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-30 7:15 aio poll and a new in-kernel poll API V21 (aka 2.0) Christoph Hellwig
2018-07-30 7:15 ` [PATCH 1/4] timerfd: add support for keyed wakeups Christoph Hellwig
2018-07-30 7:15 ` [PATCH 2/4] aio: add a iocb refcount Christoph Hellwig
2018-08-01 23:19 ` Al Viro
2018-08-02 8:59 ` Christoph Hellwig [this message]
2018-07-30 7:15 ` [PATCH 3/4] aio: implement IOCB_CMD_POLL Christoph Hellwig
2018-08-01 23:54 ` Al Viro
2018-08-02 9:00 ` Christoph Hellwig
2018-08-02 0:21 ` Al Viro
2018-08-02 9:22 ` Christoph Hellwig
2018-08-02 16:00 ` Al Viro
2018-08-02 16:08 ` Christoph Hellwig
2018-08-02 16:08 ` Al Viro
2018-08-02 16:16 ` Christoph Hellwig
2018-08-02 21:48 ` Al Viro
2018-07-30 7:15 ` [PATCH 4/4] aio: allow direct aio poll comletions for keyed wakeups Christoph Hellwig
-- strict thread matches above, loose matches on Subject: below --
2018-08-06 8:30 aio poll V22 (aka 2.0) Christoph Hellwig
2018-08-06 8:30 ` [PATCH 2/4] aio: add a iocb refcount Christoph Hellwig
2018-07-26 8:28 aio poll and a new in-kernel poll API V20 (aka 2.0) Christoph Hellwig
2018-07-26 8:29 ` [PATCH 2/4] aio: add a iocb refcount Christoph Hellwig
2018-07-26 11:22 ` Matthew Wilcox
2018-07-26 11:57 ` Christoph Hellwig
2018-07-27 8:31 ` Christoph Hellwig
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=20180802085938.GA13473@lst.de \
--to=hch@lst.de \
--cc=avi@scylladb.com \
--cc=linux-aio@kvack.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=viro@ZenIV.linux.org.uk \
/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).