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Date: Thu, 22 Dec 2016 10:31:34 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Minchan Kim <minchan@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Takashi Iwai <tiwai@suse.de>, Hyeoncheol Lee <cheol.lee@lge.com>,
        yjay.kim@lge.com, Sangseok Lee <sangseok.lee@lge.com>,
        Hugh Dickins <hughd@google.com>, "[4.7+]" <stable@vger.kernel.org>
Subject: Re: [PATCH v4 3/3] zram: support BDI_CAP_STABLE_WRITES
Message-ID: <20161222013134.GC644@jagdpanzerIV.localdomain>
References: <1482366980-3782-1-git-send-email-minchan@kernel.org>
 <1482366980-3782-4-git-send-email-minchan@kernel.org>
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On (12/22/16 09:36), Minchan Kim wrote:
> zram has used per-cpu stream feature from v4.7.
> It aims for increasing cache hit ratio of scratch buffer for
> compressing. Downside of that approach is that zram should ask
> memory space for compressed page in per-cpu context which requires
> stricted gfp flag which could be failed. If so, it retries to
> allocate memory space out of per-cpu context so it could get memory
> this time and compress the data again, copies it to the memory space.
> 
> In this scenario, zram assumes the data should never be changed
> but it is not true without stable page support. So, If the data is
> changed under us, zram can make buffer overrun so that zsmalloc
> free object chain is broken so system goes crash like below
> https://bugzilla.suse.com/show_bug.cgi?id=997574
> 
> This patch adds BDI_CAP_STABLE_WRITES to zram for declaring
> "I am block device needing *stable write*".
> 
> Fixes: da9556a2367c ("zram: user per-cpu compression streams")
> Cc: <stable@vger.kernel.org> [4.7+]
> Signed-off-by: Minchan Kim <minchan@kernel.org>

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

	-ss