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

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Message-ID: <20160425221816.GA1254@google.com>
Date:	Mon, 25 Apr 2016 15:18:16 -0700
From:	Yu Zhao <yuzhao@...gle.com>
To:	Dan Streetman <ddstreet@...e.org>
Cc:	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 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.

Or you have another patch to fix the second call path?