Re: [systemd-devel] systemd-213: regression with zram

["Alexander E. Patrakov" <patrakov@gmail.com>]

25.06.2014 06:36, Minchan Kim wrote:
> Could you test this patch? It passed my test.
> Thanks!
>
>  From 4ab4931c3fa7e6527e3a849d5e4c4f727143e66c Mon Sep 17 00:00:00 2001
> From: Minchan Kim <minchan@kernel.org>
> Date: Wed, 25 Jun 2014 09:20:24 +0900
> Subject: [PATCH] zram: revalidate disk after capacity change
>
> Alexander reported mkswap on /dev/zram0 is failed if other process
> is opening the block device file.
>
> Step is as follows,
>
> 0. Reset the unused zram device.
> 1. Use a program that opens /dev/zram0 with O_RDWR and sleeps until killed.
> 2. While that program sleeps, echo the correct value to /sys/block/zram0/disksize.
> 3. Verify (e.g. in /proc/partitions) that the disk size is applied correctly. It is.
> 4. While that program still sleeps, attempt to mkswap /dev/zram0. This fails:
> result: mkswap: error: swap area needs to be at least 40 KiB
>
> When I investigated, the size get by ioctl(fd, BLKGETSIZE64) on mkswap
> to get a size of blockdev was zero although zram0 has right size
> by 2.
>
> The reason is zram didn't revalidate disk after changing capacity
> so that size of blockdev's inode is not uptodate until all of file is close.
>
> This patch should fix the problem.
>
> Reported-by: Alexander E. Patrakov <patrakov@gmail.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>

Tested-by: Alexander E. Patrakov <patrakov@gmail.com>

It indeed fixes the problem.

> ---
>   drivers/block/zram/zram_drv.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 48eccb350180..089e72cd37be 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -622,8 +622,10 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
>   	memset(&zram->stats, 0, sizeof(zram->stats));
>
>   	zram->disksize = 0;
> -	if (reset_capacity)
> +	if (reset_capacity) {
>   		set_capacity(zram->disk, 0);
> +		revalidate_disk(zram->disk);
> +	}
>   	up_write(&zram->init_lock);
>   }
>
> @@ -664,6 +666,7 @@ static ssize_t disksize_store(struct device *dev,
>   	zram->comp = comp;
>   	zram->disksize = disksize;
>   	set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
> +	revalidate_disk(zram->disk);
>   	up_write(&zram->init_lock);
>   	return len;
>
>

-- 
Alexander E. Patrakov