From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Mon, 3 Feb 2014 15:36:28 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Weijie Yang <weijie.yang@samsung.com>
Cc: 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 3/8] mm/swap: prevent concurrent swapon on the same
 S_ISBLK blockdev
Message-Id: <20140203153628.5e186b0e4e81400773faa7ac@linux-foundation.org>
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On Mon, 27 Jan 2014 18:03:04 +0800 Weijie Yang <weijie.yang@samsung.com> wrote:

> When swapon the same S_ISBLK blockdev concurrent, the allocated two
> swap_info could hold the same block_device, because claim_swapfile()
> allow the same holder(here, it is sys_swapon function).
> 
> To prevent this situation, This patch adds swap_lock protect to ensure
> we can find this situation and return -EBUSY for one swapon call.
> 
> As for S_ISREG swapfile, claim_swapfile() already prevent this scenario
> by holding inode->i_mutex.
> 
> This patch is just for a rare scenario, aim to correct of code.
> 

hm, OK.  Would it be saner to pass a unique `holder' to
claim_swapfile()?  Say, `p'?

Truly, I am fed up with silly swapon/swapoff races.  How often does
anyone call these things?  Let's slap a huge lock around the whole
thing and be done with it?