linux-kernel - Re: [PATCH v4 1/4] zram: Fix deadlock bug in partial write

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Date:	Tue, 22 Jan 2013 10:47:17 +0100
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Minchan Kim <minchan@...nel.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Nitin Gupta <ngupta@...are.org>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	Pekka Enberg <penberg@...helsinki.fi>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v4 1/4] zram: Fix deadlock bug in partial write

On 01/22/2013 01:07 AM, Minchan Kim wrote:
> Now zram allocates new page with GFP_KERNEL in zram I/O path
> if IO is partial. Unfortunately, It may cuase deadlock with
> reclaim path so this patch solves the problem.
> 
> Cc: Nitin Gupta <ngupta@...are.org>
> Cc: Jerome Marchand <jmarchan@...hat.com>
> Cc: stable@...r.kernel.org
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
> 
> We could use GFP_IO instead of GFP_ATOMIC in zram_bvec_read with
> some modification related to buffer allocation in case of partial IO.
> But it needs more churn and prevent merge this patch into stable
> if we should send this to stable so I'd like to keep it as simple
> as possbile. GFP_IO usage could be separate patch after we merge it.
> Thanks.

I'd rather have a preallocated buffer for that. It would make
zram_bvec_read/write() simpler (no need to deal with an allocation
failure or to free the buffer) and it would be consistent with the way
other similar buffer works (compress_workmem/buffer).

Jerome

> 
>  drivers/staging/zram/zram_drv.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index 61fb8f1..b285b3a 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -220,7 +220,7 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
>  	user_mem = kmap_atomic(page);
>  	if (is_partial_io(bvec))
>  		/* Use  a temporary buffer to decompress the page */
> -		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> +		uncmem = kmalloc(PAGE_SIZE, GFP_ATOMIC);
>  	else
>  		uncmem = user_mem;
>  
> @@ -268,7 +268,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>  		 * This is a partial IO. We need to read the full page
>  		 * before to write the changes.
>  		 */
> -		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> +		uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
>  		if (!uncmem) {
>  			pr_info("Error allocating temp memory!\n");
>  			ret = -ENOMEM;
> 

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