linux-kernel - Re: [PATCH 6/7] zram: remove workqueue for freeing removed pending slot

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Date:	Tue, 14 Jan 2014 10:09:14 +0300
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, Nitin Gupta <ngupta@...are.org>,
	Jerome Marchand <jmarchan@...hat.com>
Subject: Re: [PATCH 6/7] zram: remove workqueue for freeing removed pending
 slot

Hello Minchan,

On (01/14/14 08:38), Minchan Kim wrote:
> Hello Sergey,
> 
> On Mon, Jan 13, 2014 at 10:42:56PM +0300, Sergey Senozhatsky wrote:
> > On (01/13/14 20:19), Minchan Kim wrote:
> > 
> > Hello Minchan,
> > I think we need to down_write init_lock in zram_slot_free_notify(),
> > and thus can avoid locking meta->tb_lock. otherwise, I think,
> 
> zram_slot_free_notify is atomic path so we couldn't hold mutex.
> 
> > there is a chance that zram_slot_free_notify() can race with
> > device reset, e.g.
> > 	
> > 	zram_slot_free_notify()			zram_reset_device()
> > 						down_write(&zram->init_lock);
> > 	meta = zram->meta
> > 						zram_meta_free(zram->meta);
> > 						zram->meta = NULL;
> > 	write_lock(&meta->tb_lock);
> > 	[...]
> > 	write_unlock(&meta->tb_lock);
> > 						[..]
> > 						up_write(&zram->init_lock);
> > 
> 
> Nope. We couldn't reset active device by bdev->bd_holders check
> logic in reset_store.
> 

true. sorry for the noise.

	-ss
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