[PATCH v2 5/6] PCI: hv: hv_pci_devices_present(): only queue a new work when necessary

[Dexuan Cui <decui@microsoft.com>]

If there is a pending work, we just need to add the new dr into
the dr_list.

This is suggested by Michael Kelley.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Jack Morgenstein <jackm@mellanox.com>
Cc: stable@vger.kernel.org
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Michael Kelley (EOSG) <Michael.H.Kelley@microsoft.com>
---
 drivers/pci/host/pci-hyperv.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/host/pci-hyperv.c b/drivers/pci/host/pci-hyperv.c
index 3a385212f666..d3aa6736a9bb 100644
--- a/drivers/pci/host/pci-hyperv.c
+++ b/drivers/pci/host/pci-hyperv.c
@@ -1733,6 +1733,7 @@ static void hv_pci_devices_present(struct hv_pcibus_device *hbus,
 	struct hv_dr_state *dr;
 	struct hv_dr_work *dr_wrk;
 	unsigned long flags;
+	bool pending_dr;
 
 	dr_wrk = kzalloc(sizeof(*dr_wrk), GFP_NOWAIT);
 	if (!dr_wrk)
@@ -1756,11 +1757,23 @@ static void hv_pci_devices_present(struct hv_pcibus_device *hbus,
 	}
 
 	spin_lock_irqsave(&hbus->device_list_lock, flags);
+
+	/*
+	 * If pending_dr is true, we have already queued a work,
+	 * which will see the new dr. Otherwise, we need to
+	 * queue a new work.
+	 */
+	pending_dr = !list_empty(&hbus->dr_list);
 	list_add_tail(&dr->list_entry, &hbus->dr_list);
-	spin_unlock_irqrestore(&hbus->device_list_lock, flags);
 
-	get_hvpcibus(hbus);
-	queue_work(hbus->wq, &dr_wrk->wrk);
+	if (pending_dr) {
+		kfree(dr_wrk);
+	} else {
+		get_hvpcibus(hbus);
+		queue_work(hbus->wq, &dr_wrk->wrk);
+	}
+
+	spin_unlock_irqrestore(&hbus->device_list_lock, flags);
 }
 
 /**
-- 
2.7.4
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