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Date:	Sun, 27 Dec 2015 18:36:29 -0500
From:	Rafael Aquini <aquini@...hat.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Michael S. Tsirkin" <mst@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Konstantin Khlebnikov <koct9i@...il.com>,
	stable@...r.kernel.org
Subject: Re: [PATCH 2/2] virtio_balloon: fix race between migration and
 ballooning

On Mon, Dec 28, 2015 at 08:35:13AM +0900, Minchan Kim wrote:
> In balloon_page_dequeue, pages_lock should cover the loop
> (ie, list_for_each_entry_safe). Otherwise, the cursor page could
> be isolated by compaction and then list_del by isolation could
> poison the page->lru.{prev,next} so the loop finally could
> access wrong address like this. This patch fixes the bug.
> 
> general protection fault: 0000 [#1] SMP
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Modules linked in:
> CPU: 2 PID: 82 Comm: vballoon Not tainted 4.4.0-rc5-mm1-access_bit+ #1906
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> task: ffff8800a7ff0000 ti: ffff8800a7fec000 task.ti: ffff8800a7fec000
> RIP: 0010:[<ffffffff8115e754>]  [<ffffffff8115e754>] balloon_page_dequeue+0x54/0x130
> RSP: 0018:ffff8800a7fefdc0  EFLAGS: 00010246
> RAX: ffff88013fff9a70 RBX: ffffea000056fe00 RCX: 0000000000002b7d
> RDX: ffff88013fff9a70 RSI: ffffea000056fe00 RDI: ffff88013fff9a68
> RBP: ffff8800a7fefde8 R08: ffffea000056fda0 R09: 0000000000000000
> R10: ffff8800a7fefd90 R11: 0000000000000001 R12: dead0000000000e0
> R13: ffffea000056fe20 R14: ffff880138809070 R15: ffff880138809060
> FS:  0000000000000000(0000) GS:ffff88013fc40000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> CR2: 00007f229c10e000 CR3: 00000000b8b53000 CR4: 00000000000006a0
> Stack:
>  0000000000000100 ffff880138809088 ffff880138809000 ffff880138809060
>  0000000000000046 ffff8800a7fefe28 ffffffff812c86d3 ffff880138809020
>  ffff880138809000 fffffffffff91900 0000000000000100 ffff880138809060
> Call Trace:
>  [<ffffffff812c86d3>] leak_balloon+0x93/0x1a0
>  [<ffffffff812c8bc7>] balloon+0x217/0x2a0
>  [<ffffffff8143739e>] ? __schedule+0x31e/0x8b0
>  [<ffffffff81078160>] ? abort_exclusive_wait+0xb0/0xb0
>  [<ffffffff812c89b0>] ? update_balloon_stats+0xf0/0xf0
>  [<ffffffff8105b6e9>] kthread+0xc9/0xe0
>  [<ffffffff8105b620>] ? kthread_park+0x60/0x60
>  [<ffffffff8143b4af>] ret_from_fork+0x3f/0x70
>  [<ffffffff8105b620>] ? kthread_park+0x60/0x60
> Code: 8d 60 e0 0f 84 af 00 00 00 48 8b 43 20 a8 01 75 3b 48 89 d8 f0 0f ba 28 00 72 10 48 8b 03 f6 c4 08 75 2f 48 89 df e8 8c 83 f9 ff <49> 8b 44 24 20 4d 8d 6c 24 20 48 83 e8 20 4d 39 f5 74 7a 4c 89
> RIP  [<ffffffff8115e754>] balloon_page_dequeue+0x54/0x130
>  RSP <ffff8800a7fefdc0>
> ---[ end trace 43cf28060d708d5f ]---
> Kernel panic - not syncing: Fatal exception
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Kernel Offset: disabled
> 
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
>  mm/balloon_compaction.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
> index d3116be5a00f..300117f1a08f 100644
> --- a/mm/balloon_compaction.c
> +++ b/mm/balloon_compaction.c
> @@ -61,6 +61,7 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
>  	bool dequeued_page;
>  
>  	dequeued_page = false;
> +	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
>  	list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
>  		/*
>  		 * Block others from accessing the 'page' while we get around
> @@ -75,15 +76,14 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
>  				continue;
>  			}
>  #endif
> -			spin_lock_irqsave(&b_dev_info->pages_lock, flags);
>  			balloon_page_delete(page);
>  			__count_vm_event(BALLOON_DEFLATE);
> -			spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
>  			unlock_page(page);
>  			dequeued_page = true;
>  			break;
>  		}
>  	}
> +	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
>  
>  	if (!dequeued_page) {
>  		/*
> -- 
> 1.9.1
> 
Acked-by: Rafael Aquini <aquini@...hat.com>
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