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Date: Thu, 2 Aug 2018 00:19:56 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Christoph Hellwig <hch@lst.de>
Cc: Avi Kivity <avi@scylladb.com>, linux-aio@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/4] aio: add a iocb refcount
Message-ID: <20180801231956.GS30522@ZenIV.linux.org.uk>
References: <20180730071544.23998-1-hch@lst.de>
 <20180730071544.23998-3-hch@lst.de>
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On Mon, Jul 30, 2018 at 09:15:42AM +0200, Christoph Hellwig wrote:
> This is needed to prevent races caused by the way the ->poll API works.
> To avoid introducing overhead for other users of the iocbs we initialize
> it to zero and only do refcount operations if it is non-zero in the
> completion path.

refcount_t looks like a bad match - you, AFAICS, have count 0 for everything
except poll, while for poll you start with 2.  That looks like
	if (iocb->shared && test_and_clear_bit(0, &iocb->shared))
		return;
	kill the sucker
in your iocb_put() and initializing it to 1 in poll.  No?