linux-kernel - Re: [PATCH v3 02/10] zram: use zram->lock to protect zram_free

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Date:	Fri, 07 Jun 2013 11:32:21 +0200
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Jiang Liu <liuj97@...il.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Nitin Gupta <ngupta@...are.org>,
	Minchan Kim <minchan@...nel.org>,
	Jiang Liu <jiang.liu@...wei.com>, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v3 02/10] zram: use zram->lock to protect zram_free_page()
 in swap free notify path

On 06/06/2013 06:07 PM, Jiang Liu wrote:
> zram_slot_free_notify() is free-running without any protection from
> concurrent operations. So there are race conditions between
> zram_bvec_read()/zram_bvec_write() and zram_slot_free_notify(),
> and possible consequences include:
> 1) Trigger BUG_ON(!handle) on zram_bvec_write() side.
> 2) Access to freed pages on zram_bvec_read() side.
> 3) Break some fields (bad_compress, good_compress, pages_stored)
>    in zram->stats if the swap layer makes concurrently call to
>    zram_slot_free_notify().
> 
> So enhance zram_slot_free_notify() to acquire writer lock on zram->lock
> before calling zram_free_page().
> 
> Signed-off-by: Jiang Liu <jiang.liu@...wei.com>
> Cc: stable@...r.kernel.org

Acked-by: Jerome Marchand <jmarchand@...hat.com>


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