linux-kernel - Re: [RESEND PATCH v5 1/4] zram: Fix deadlock bug in partial write

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Date:	Mon, 28 Jan 2013 09:16:35 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Nitin Gupta <ngupta@...are.org>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	stable@...r.kernel.org, Jerome Marchand <jmarchan@...hat.com>
Subject: Re: [RESEND PATCH v5 1/4] zram: Fix deadlock bug in partial write

On Mon, Jan 28, 2013 at 2:38 AM, Minchan Kim <minchan@...nel.org> wrote:
> Now zram allocates new page with GFP_KERNEL in zram I/O path
> if IO is partial. Unfortunately, It may cuase deadlock with

s/cuase/cause/g

> reclaim path so this patch solves the problem.

It'd be nice to know about the problem in more detail. I'm also
curious on why you decided on GFP_ATOMIC for the read path and
GFP_NOIO in the write path.

>
> Cc: stable@...r.kernel.org
> Cc: Jerome Marchand <jmarchan@...hat.com>
> Acked-by: Nitin Gupta <ngupta@...are.org>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
>  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;
> --
> 1.7.9.5
>
> --
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