linux-kernel - Re: [PATCH] zram: avoid kunmap

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Message-ID: <20141031134632.GA942@swordfish>
Date:	Fri, 31 Oct 2014 22:46:32 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Weijie Yang <weijie.yang@...sung.com>
Cc:	'Minchan Kim' <minchan@...nel.org>,
	'Andrew Morton' <akpm@...ux-foundation.org>,
	'Sergey Senozhatsky' <sergey.senozhatsky@...il.com>,
	'Dan Streetman' <ddstreet@...e.org>,
	'Nitin Gupta' <ngupta@...are.org>,
	'Weijie Yang' <weijie.yang.kh@...il.com>,
	'Linux-MM' <linux-mm@...ck.org>,
	'linux-kernel' <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] zram: avoid kunmap_atomic a NULL pointer

On (10/30/14 14:20), Weijie Yang wrote:
> zram could kunmap_atomic a NULL pointer in a rare situation:
> a zram page become a full-zeroed page after a partial write io.
> The current code doesn't handle this case and kunmap_atomic a
> NULL porinter, which panic the kernel.
> 
> This patch fixes this issue.
> 
> Signed-off-by: Weijie Yang <weijie.yang@...sung.com>

thank you, Weijie.

Acked-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

	-ss

> ---
>  drivers/block/zram/zram_drv.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 2ad0b5b..3920ee4 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -560,7 +560,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>  	}
>  
>  	if (page_zero_filled(uncmem)) {
> -		kunmap_atomic(user_mem);
> +		if (user_mem)
> +			kunmap_atomic(user_mem);
>  		/* Free memory associated with this sector now. */
>  		bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
>  		zram_free_page(zram, index);
> -- 
> 1.7.0.4
> 
> 
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