linux-kernel - Re: [PATCH 1/4] Staging: zram: Remove useless offset calculation in handle_uncompressed

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Date:	Fri, 10 Jun 2011 09:38:00 -0700
From:	Nitin Gupta <ngupta@...are.org>
To:	Jerome Marchand <jmarchan@...hat.com>
CC:	Greg Kroah-Hartman <gregkh@...e.de>,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>,
	Jeff Moyer <jmoyer@...hat.com>
Subject: Re: [PATCH 1/4] Staging: zram: Remove useless offset calculation
 in handle_uncompressed_page()

On 06/10/2011 06:28 AM, Jerome Marchand wrote:
> The offset of uncompressed page is always zero: handle_uncompressed_page()
> doesn't have to care about it.
>
> Signed-off-by: Jerome Marchand<jmarchan@...hat.com>
> ---
>   drivers/staging/zram/zram_drv.c |    3 +--
>   1 files changed, 1 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index aab4ec4..3305e1a 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -194,8 +194,7 @@ static void handle_uncompressed_page(struct zram *zram,
>   	unsigned char *user_mem, *cmem;
>
>   	user_mem = kmap_atomic(page, KM_USER0);
> -	cmem = kmap_atomic(zram->table[index].page, KM_USER1) +
> -			zram->table[index].offset;
> +	cmem = kmap_atomic(zram->table[index].page, KM_USER1);
>
>   	memcpy(user_mem, cmem, PAGE_SIZE);
>   	kunmap_atomic(user_mem, KM_USER0);


kmap/kunmap requests needs to be strictly nested, so here kunmap(..., 
KM_USER1) must be done before kunmap(..., KM_USER0). This needs to be
fixed in zram_bvec_read() also.  Though these bugs are not introduced
by your patches, it would be nice to have them include them in your 
patch series only.

Thanks for the fixes.
Nitin

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