linux-kernel - Re: [PATCH v1 01/10] zram: avoid calling of zram_meta_free under init

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Date:	Wed, 21 Jan 2015 23:21:53 +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, linux-mm@...ck.org,
	Dan Streetman <ddstreet@...e.org>,
	Seth Jennings <sjennings@...iantweb.net>,
	Nitin Gupta <ngupta@...are.org>,
	Juneho Choi <juno.choi@....com>, Gunho Lee <gunho.lee@....com>,
	Luigi Semenzato <semenzato@...gle.com>,
	Jerome Marchand <jmarchan@...hat.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH v1 01/10] zram: avoid calling of zram_meta_free under
 init_lock

On (01/21/15 15:14), Minchan Kim wrote:
> We don't need to call zram_meta_free under init_lock.
> What we need to prevent race is setting NULL into zram->meta
> (ie, init_done). This patch does it.
> 
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
>  drivers/block/zram/zram_drv.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 9250b3f..7e03d86 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -719,6 +719,8 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
>  	}
>  
>  	meta = zram->meta;
> +	zram->meta = NULL;
> +
>  	/* Free all pages that are still in this zram device */
>  	for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
>  		unsigned long handle = meta->table[index].handle;
> @@ -731,8 +733,6 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
>  	zcomp_destroy(zram->comp);
>  	zram->max_comp_streams = 1;
>  
> -	zram_meta_free(zram->meta);
> -	zram->meta = NULL;
>  	/* Reset stats */
>  	memset(&zram->stats, 0, sizeof(zram->stats));
>  
> @@ -741,6 +741,7 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
>  		set_capacity(zram->disk, 0);
>  
>  	up_write(&zram->init_lock);
> +	zram_meta_free(meta);

Hello,

since we detached ->meta from zram, this one doesn't really need
->init_lock protection:

	/* Free all pages that are still in this zram device */
	for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
		unsigned long handle = meta->table[index].handle;
		if (!handle)
			continue;

		zs_free(meta->mem_pool, handle);
	}


	-ss

>  	/*
>  	 * Revalidate disk out of the init_lock to avoid lockdep splat.
> -- 
> 1.9.3
> 
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