linux-kernel - Re: [PATCH] mm/zpool: use workqueue for zpool

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Date:	Tue, 26 Apr 2016 09:59:19 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Yu Zhao <yuzhao@...gle.com>
Cc:	Dan Streetman <ddstreet@...e.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Seth Jennings <sjenning@...hat.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	Nitin Gupta <ngupta@...are.org>, Linux-MM <linux-mm@...ck.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Dan Streetman <dan.streetman@...onical.com>
Subject: Re: [PATCH] mm/zpool: use workqueue for zpool_destroy

On (04/25/16 15:18), Yu Zhao wrote:
> On Mon, Apr 25, 2016 at 05:20:10PM -0400, Dan Streetman wrote:
> > Add a work_struct to struct zpool, and change zpool_destroy_pool to
> > defer calling the pool implementation destroy.
> > 
> > The zsmalloc pool destroy function, which is one of the zpool
> > implementations, may sleep during destruction of the pool.  However
> > zswap, which uses zpool, may call zpool_destroy_pool from atomic
> > context.  So we need to defer the call to the zpool implementation
> > to destroy the pool.
> > 
> > This is essentially the same as Yu Zhao's proposed patch to zsmalloc,
> > but moved to zpool.
> 
> Thanks, Dan. Sergey also mentioned another call path that triggers the
> same problem (BUG: scheduling while atomic):
>   rcu_process_callbacks()
>           __zswap_pool_release()
>                   zswap_pool_destroy()
>                           zswap_cpu_comp_destroy()
>                                   cpu_notifier_register_begin()
>                                           mutex_lock(&cpu_add_remove_lock);
> So I was thinking zswap_pool_destroy() might be done in workqueue in zswap.c.
> This way we fix both call paths.

right, I'm not sure the patch addressed all of the issues.

	-ss