linux-kernel - Re: [PATCH 2/4] aio: add a iocb refcount

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Date:   Thu, 2 Aug 2018 00:19:56 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Christoph Hellwig <hch@....de>
Cc:     Avi Kivity <avi@...lladb.com>, linux-aio@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] aio: add a iocb refcount

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?