Re: [PATCH v7 1/4] zram: Fix deadlock bug in partial read/write

[Minchan Kim]

Hi Greg,

I added all Acked-by and rebased on next-20130202.
Please apply this.

On Mon, Feb 04, 2013 at 08:46:08AM +0900, Minchan Kim wrote:
> Now zram allocates new page with GFP_KERNEL in zram I/O path
> if IO is partial. Unfortunately, It may cause deadlock with
> reclaim path like below.
> 
> write_page from fs
> fs_lock
> allocation(GFP_KERNEL)
> reclaim
> pageout
> 				write_page from fs
> 				fs_lock <-- deadlock
> 
> This patch fixes it by using GFP_NOIO.  In read path, we
> reorganize code flow so that kmap_atomic is called after the
> GFP_NOIO allocation.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Acked-by: Jerome Marchand <jmarchan@xxxxxxxxxx>
> Acked-by: Nitin Gupta <ngupta@xxxxxxxxxx>
> [ penberg@xxxxxxxxxx: don't use GFP_ATOMIC ]
> Signed-off-by: Pekka Enberg <penberg@xxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> ---
>  drivers/staging/zram/zram_drv.c |    9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index 941b7c6..262265e 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -217,11 +217,12 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
>  		return 0;
>  	}
>  
> -	user_mem = kmap_atomic(page);
>  	if (is_partial_io(bvec))
>  		/* Use  a temporary buffer to decompress the page */
> -		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> -	else
> +		uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
> +
> +	user_mem = kmap_atomic(page);
> +	if (!is_partial_io(bvec))
>  		uncmem = user_mem;
>  
>  	if (!uncmem) {
> @@ -268,7 +269,7 @@ 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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-- 
Kind regards,
Minchan Kim
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