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

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Date:	Mon, 28 Jan 2013 12:24:04 +0100
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Pekka Enberg <penberg@...nel.org>
CC:	Minchan Kim <minchan@...nel.org>,
	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
Subject: Re: [RESEND PATCH v5 1/4] zram: Fix deadlock bug in partial write

On 01/28/2013 08:16 AM, Pekka Enberg wrote:
> 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.

This is because we're holding a kmap_atomic page in the read path.

Jerome

> 
>>
>> 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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