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Date: Mon, 3 Feb 2014 15:29:25 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Weijie Yang <weijie.yang@samsung.com>, hughd@google.com,
	"'Minchan Kim'" <minchan@kernel.org>, shli@kernel.org,
	"'Bob Liu'" <bob.liu@oracle.com>, weijie.yang.kh@gmail.com,
	"'Seth Jennings'" <sjennings@variantweb.net>,
	"'Heesub Shin'" <heesub.shin@samsung.com>, mquzik@redhat.com,
	"'Linux-MM'" <linux-mm@kvack.org>,
	"'linux-kernel'" <linux-kernel@vger.kernel.org>,
	stable@vger.kernel.org
Subject: Re: [PATCH 2/8] mm/swap: fix race on swap_info reuse between
 swapoff and swapon
Message-Id: <20140203152925.89360139306d143f5360fa07@linux-foundation.org>
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References: <000d01cf1b47$f12e11f0$d38a35d0$%yang@samsung.com>
	<20140203152340.b28bb35698ee75615eb23041@linux-foundation.org>
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On Mon, 3 Feb 2014 15:23:40 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:

> On Mon, 27 Jan 2014 18:03:04 +0800 Weijie Yang <weijie.yang@samsung.com> wrote:
> 
> > swapoff clear swap_info's SWP_USED flag prematurely and free its resources
> > after that. A concurrent swapon will reuse this swap_info while its previous
> > resources are not cleared completely.
> > 
> > These late freed resources are:
> >  - p->percpu_cluster
> >  - swap_cgroup_ctrl[type]
> >  - block_device setting
> >  - inode->i_flags &= ~S_SWAPFILE
> > 
> > This patch clear SWP_USED flag after all its resources freed, so that swapon
> > can reuse this swap_info by alloc_swap_info() safely.
> > 
> > This patch is just for a rare scenario, aim to correct of code.
> 
> I believe that
> http://ozlabs.org/~akpm/mmots/broken-out/mm-swap-fix-race-on-swap_info-reuse-between-swapoff-and-swapon.patch
> makes this patch redundant?
> 

oop, hang on.  This patch *is* a stealth-updated version of
http://ozlabs.org/~akpm/mmots/broken-out/mm-swap-fix-race-on-swap_info-reuse-between-swapoff-and-swapon.patch.

Undocumented removals of si->swap_map have been added.  What's going on
there?

I think I'll stick with the original patch for now.  If you see
additional optimisations or changes, let's address that separately?