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

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Message-Id: <7AFB0C38-3D2E-45E8-9092-CA424BFD32B6@dilger.ca>
Date:   Wed, 6 Dec 2017 19:38:48 -0700
From:   Andreas Dilger <adilger@...ger.ca>
To:     Ingo Molnar <mingo@...nel.org>
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

> 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?

Alternately, a helper that returns the pointer to the lock:

#define waitqueue_lockp(wq) &((wq)->lock)

Used like the following:
        spin_lock_irqsave(waitqueue_lockp(&ep->wq), flags);

Cheers, Andreas