linux-kernel - Re: [PATCH 1/7] zram: fix race between reset and flushing pending work

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Date:	Mon, 13 Jan 2014 15:55:27 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Minchan Kim <minchan@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Nitin Gupta <ngupta@...are.org>,
	Jerome Marchand <jmarchan@...hat.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	stable <stable@...r.kernel.org>
Subject: Re: [PATCH 1/7] zram: fix race between reset and flushing pending
 work

On Mon, 13 Jan 2014 20:18:56 +0900 Minchan Kim <minchan@...nel.org> wrote:

> Dan and Sergey reported that there is a racy between reset and
> flushing of pending work so that it could make oops by freeing
> zram->meta in reset while zram_slot_free can access zram->meta
> if new request is adding during the race window.
> 
> This patch moves flush after taking init_lock so it prevents
> new request so that it closes the race.
> 
> ..
>
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -553,14 +553,14 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
>  	size_t index;
>  	struct zram_meta *meta;
>  
> -	flush_work(&zram->free_work);
> -
>  	down_write(&zram->init_lock);
>  	if (!zram->init_done) {
>  		up_write(&zram->init_lock);
>  		return;
>  	}
>  
> +	flush_work(&zram->free_work);
> +
>  	meta = zram->meta;
>  	zram->init_done = 0;

This makes zram.lock nest inside zram.init_lock, which afaict is new
behaviour.

That all seems OK and logical - has it been well tested with lockdep?
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