linux-kernel - Re: [PATCH 07/36] aio: add delayed cancel support

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Message-ID: <20180320152022.GB23920@lst.de>
Date:   Tue, 20 Mar 2018 16:20:22 +0100
From:   Christoph Hellwig <hch@....de>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     Christoph Hellwig <hch@....de>, viro@...iv.linux.org.uk,
        Avi Kivity <avi@...lladb.com>, linux-aio@...ck.org,
        linux-fsdevel@...r.kernel.org, netdev@...r.kernel.org,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/36] aio: add delayed cancel support

On Mon, Mar 19, 2018 at 08:19:57PM -0700, Darrick J. Wong wrote:
> On Mon, Mar 05, 2018 at 01:27:14PM -0800, Christoph Hellwig wrote:
> > The upcoming aio poll support would like to be able to complete the
> > iocb inline from the cancellation context, but that would cause
> > a lock order reversal.  Add support for optionally moving the cancelation
> > outside the context lock to avoid this reversal.
> 
> I started to wonder which lock order reversal the commit message refers
> to?
> 
> I think the reason for adding delayed cancellations is that we want to
> be able to call io_cancel -> kiocb_cancel -> aio_poll_cancel ->
> aio_complete without double locking ctx_lock?

It is.  I've updated the commit message.