linux-kernel - Re: [PATCH 1/2] epoll: use the waitqueue lock to protect ep->wq

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Date:   Thu, 7 Dec 2017 07:12:13 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Andreas Dilger <adilger@...ger.ca>
Cc:     Christoph Hellwig <hch@....de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jason Baron <jbaron@...mai.com>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] epoll: use the waitqueue lock to protect ep->wq


* Andreas Dilger <adilger@...ger.ca> wrote:

> > On Dec 6, 2017, at 17:49, Ingo Molnar <mingo@...nel.org> wrote:
> > 
> > This exposes some waitqueue internals, but AFAICS the FUSE code already does a 
> > similar trick with fiq->waitq.lock so there's precedent.
> 
> What about waitqueue_lock() and waitqueue_unlock() helpers that
> lock and unlock, to avoid exposing the internals?  Or would that add
> confusion by making users think they need their own waitqueue locking?

Right now there are just two users (FUSE and epoll), and both are well-maintained, 
essentially core kernel code - I'd rather prefer the readability of explicitly 
writing out the locking/unlocking pattern.

So while it's a mild layering violation, it's also a valid looking optimization.

Thanks,

	Ingo