Re: [PATCH v1 2/2] zram: remove init_lock in zram_make_request

[Minchan Kim <minchan@kernel.org>]

On Mon, Feb 02, 2015 at 02:59:23PM +0900, Sergey Senozhatsky wrote:
> On (02/02/15 12:41), Minchan Kim wrote:
> > > If we use zram as block device itself(not a fs or swap) and open the
> > > block device as !FMODE_EXCL, bd_holders will be void.
> > > 
> > > Another topic: As I didn't see enough fs/block_dev.c bd_holders in zram
> > > would be mess. I guess we need to study hotplug of device and implement
> > > it for zram reset rather than strange own konb. It should go TODO. :(
> > 
> > Actually, I thought bd_mutex use from custom driver was terrible idea
> > so we should walk around with device hotplug but as I look through
> > another drivers, they have used the lock for a long time.
> > Maybe it's okay to use it in zram?
> > If so, Ganesh's patch is no problem to me although I didn't' review it in detail.
> > One thing I want to point out is that it would be better to change bd_holders
> > with bd_openers to filter out because dd test opens block device as !EXCL
> > so bd_holders will be void.
> > 
> > What do you think about it?
> > 
> 
> a quick idea:
> can we additionally move all bd flush and put work after zram_reset_device(zram, true)
> and, perhaps, replace ->bd_holders with something else?
> 
> zram_reset_device() will not return until we have active IOs, pending IOs will be
> invalidated by ->disksize != 0.

Sorry, I don't get it. Could you describe what you are concerning about active I/O?
My concern is just race bd_holder/bd_openers and bd_holders of zram check.
I don't think any simple solution without bd_mutex.
If we can close the race, anything could be a solution.
If we close the race, we should return -EBUSY if anyone is opening the zram device
so bd_openers check would be better than bd_holders.

> 
> 	-ss

-- 
Kind regards,
Minchan Kim

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