linux-kernel - Re: [PATCH 3/4] aio: implement IOCB_CMD

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Message-ID: <20180802160032.GY30522@ZenIV.linux.org.uk>
Date:   Thu, 2 Aug 2018 17:00:32 +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 3/4] aio: implement IOCB_CMD_POLL

On Thu, Aug 02, 2018 at 11:22:34AM +0200, Christoph Hellwig wrote:

> Yes, I think you are right. I'll see how I could handle that case.
> One of the easiest options would be to just support aio poll on
> file ops that support keyed wakeups, we'd just need to pass that
> information up.

BTW, what happens if we insert into one queue and immediately get
woken up, even before the damn thing gets to the end of ->poll(),
which proceeds to call poll_wait() again (on another queue)?
AFAICS, apt.error will be set by the second callback and completely
ignored.  And so will the return value of ->poll()...

Sigh...  Analysis of that thing is bloody painful, mostly because
it's hard to describe the state...