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Date: Thu, 18 Oct 2018 15:56:11 -0700
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] userfaultfd: disable irqs when taking the waitqueue
 lock
Message-Id: <20181018155611.42b9977ba08419b7869619c5@linux-foundation.org>
In-Reply-To: <20181018154101.18750-1-hch@lst.de>
References: <20181018154101.18750-1-hch@lst.de>
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To: Christoph Hellwig <hch@lst.de>
Cc: linux-mm@kvack.org

On Thu, 18 Oct 2018 17:41:01 +0200 Christoph Hellwig <hch@lst.de> wrote:

> userfaultfd contains howe-grown locking of the waitqueue lock,
> and does not disable interrupts.  This relies on the fact that
> no one else takes it from interrupt context and violates an
> invariat of the normal waitqueue locking scheme.  With aio poll
> it is easy to trigger other locks that disable interrupts (or
> are called from interrupt context).

So...  this is needed in 4.19.x but not earlier?  Or something else?