linux-kernel - Re: [PATCH] zram: revalidate disk after capacity change

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Message-ID: <20140626103158.GA987@swordfish>
Date:	Thu, 26 Jun 2014 19:31:59 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	"Alexander E. Patrakov" <patrakov@...il.com>,
	Nitin Gupta <ngupta@...are.org>,
	Jerome Marchand <jmarchan@...hat.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	stable@...r.kernel.org
Subject: Re: [PATCH] zram: revalidate disk after capacity change

On (06/26/14 10:16), Minchan Kim wrote:
> 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: mkswap: error: swap area needs to be at least 40 KiB
> 
> When I investigated, the size get by ioctl(fd, BLKGETSIZE64, xxx)
> 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 BUG.
> 

Good catch

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

	-ss

> Cc: stable@...r.kernel.org
> Reported-and-Tested-by: Alexander E. Patrakov <patrakov@...il.com>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
>  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 48eccb3..089e72c 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;
>  
> -- 
> 2.0.0
> 
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