From 15e26f6a3c6de2c665b4a30b9a70a902111f281f Mon Sep 17 00:00:00 2001
From: Lars Ellenberg <lars.ellenberg@linbit.com>
Date: Mon, 28 Apr 2014 11:43:21 +0200
Subject: [PATCH] drbd: add drbd_queue_work_if_unqueued helper

We sometimes do
    if (list_empty(&w.list))
	drbd_queue_work(&q, &w.list);

Removal (list_del_init) may happen outside all locks, after all
pending work entries have been moved to an on-stack local work list.

For not dynamically allocated, but embeded, work structs,
we must avoid to re-add until it really was removed.

Move that list_empty check inside the spin_lock(&q->q_lock)
within the helper function, and change to list_empty_careful().

This may have been the reason for a list_add corruption
inside drbd_queue_work().

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
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