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

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Message-ID: <CALZtONCs3pTmdy55u=31P75pr61SUya=f=rS7px4gRXxR6gYZA@mail.gmail.com>
Date:	Tue, 26 Apr 2016 07:07:45 -0400
From:	Dan Streetman <ddstreet@...e.org>
To:	Yu Zhao <yuzhao@...gle.com>
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 6:18 PM, Yu Zhao <yuzhao@...gle.com> 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.

Yes, you're right, I took so long to get around to this I forgot the details :-)

I'll send a new patch to zswap.

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