From: Benjamin LaHaise <bcrl@kvack.org>
To: Tang Chen <tangchen@cn.fujitsu.com>
Cc: viro@zeniv.linux.org.uk, jmoyer@redhat.com,
kosaki.motohiro@gmail.com, kosaki.motohiro@jp.fujitsu.com,
isimatu.yasuaki@jp.fujitsu.com, guz.fnst@cn.fujitsu.com,
linux-fsdevel@vger.kernel.org, linux-aio@kvack.org,
linux-kernel@vger.kernel.org, miaox@cn.fujitsu.com
Subject: Re: [RESEND v2 PATCH 1/2] aio, memory-hotplug: Fix confliction when migrating and accessing ring pages.
Date: Wed, 12 Mar 2014 18:17:36 -0400 [thread overview]
Message-ID: <20140312221735.GF32444@kvack.org> (raw)
In-Reply-To: <531FEFC6.50709@cn.fujitsu.com>
Hello Tang,
On Wed, Mar 12, 2014 at 01:25:26PM +0800, Tang Chen wrote:
... <snip> ...
> >Another spot is in
> >aio_read_events_ring() where head and tail are fetched from the ring
> >without
> >any locking. I also fear we'll be introducing new performance issues with
> >all the additonal spinlock bouncing, despite the fact that is only ever
> >needed for migration. I'm going to continue looking into this today and
> >will try to send out a followup to this email later.
>
> In the beginning of aio_read_events_ring(), it reads head and tail, not
> write.
> So even if ring pages are migrated, the contents of the pages will not
> be changed.
> So reading it is OK, from old page or from the new page, I think.
Your assumption that reading it is okay is incorrect. Since we do not have
a reference on the page at that point, it is possible that the read of the
page takes place after the page has been freed and allocated to another part
of the kernel. This would result in the read returning invalid information.
-ben
--
"Thought is the essence of where you are now."
next prev parent reply other threads:[~2014-03-12 22:17 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-10 8:15 [RESEND v2 PATCH 0/2] Bug fix in aio ring page migration Tang Chen
2014-03-10 8:15 ` [RESEND v2 PATCH 1/2] aio, memory-hotplug: Fix confliction when migrating and accessing ring pages Tang Chen
2014-03-11 18:46 ` Benjamin LaHaise
2014-03-12 5:25 ` Tang Chen
2014-03-12 22:17 ` Benjamin LaHaise [this message]
2014-03-14 10:25 ` Gu Zheng
2014-03-14 15:14 ` Benjamin LaHaise
2014-03-16 2:06 ` Gu Zheng
2014-03-17 6:50 ` Tang Chen
2014-03-10 8:15 ` [RESEND v2 PATCH 2/2] aio, mem-hotplug: Add memory barrier to aio ring page migration Tang Chen
2014-03-13 9:45 ` [RESEND v2 PATCH 0/2] Bug fix in " Gu Zheng
2014-03-16 21:21 ` Ben Hutchings
2014-05-13 23:58 ` Greg Kroah-Hartman
2014-05-14 1:13 ` Gu Zheng
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