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Date: Wed, 29 Apr 2015 16:23:28 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Minchan Kim <minchan@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, Nitin Gupta <ngupta@vflare.org>,
        linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [PATCHv3 9/9] zram: add dynamic device add/remove functionality
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On (04/29/15 16:02), Sergey Senozhatsky wrote:
> sure. I was talking about this one:
> 
> 	CPU0			CPU1
> 	umount
> 	zram_remove()
> 	lock ->bd_mutex
> 	zram_reset_device()
> 	unlock ->bd_mutex
> 				disksize_store
> 				mount
> 				echo 'test' > /mnt/test
> 	kfree zram
> 				zram write
> 

I'll take a look later today. currently I think of something like:


	sysfs_remove_group()
	lock ->bd_mutex
		... check ->bd_openers

	zram_reset_device()
	blk_cleanup_queue()
	del_gendisk()
	put_disk()

	unlock ->bd_mutex
	bdput bdev

	idr_remove()
	kfree(zram)


iow, idr_remove() and kfree() are done outside of ->bd_mutex lock.
but I may be wrong. haven't tested yet. but seems reasonable: we
invalidate ->bdev, delete partitions, etc., holding ->bd_mutex and
then release ->bdev, which does final put. need to check that in
detail.

	-ss