From 687b0ad2751ca8ea418396fa780e22571fba76a8 Mon Sep 17 00:00:00 2001
From: Kent Overstreet <kmo@daterainc.com>
Date: Mon, 6 Jan 2014 13:13:26 -0800
Subject: [PATCH] percpu-refcount: Add a WARN() for ref going negative

AIO had a missing get, which led to an ioctx leak - after percpu_ref_kill() the
ref was 0 so percpu_ref_put() never saw it hit 0.

This wasn't noticed at the time because it all happened completely silently,
this adds a WARN() which would've caught the aio bug.

tj: Used WARN_ONCE() instead of WARN().

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
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