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Date: Mon, 25 Apr 2016 15:18:16 -0700
From: Yu Zhao <yuzhao@google.com>
To: Dan Streetman <ddstreet@ieee.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Seth Jennings <sjenning@redhat.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Minchan Kim <minchan@kernel.org>, Nitin Gupta <ngupta@vflare.org>,
        Linux-MM <linux-mm@kvack.org>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Dan Streetman <dan.streetman@canonical.com>
Subject: Re: [PATCH] mm/zpool: use workqueue for zpool_destroy
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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?