[SRU][Bionic][PATCH 3/3] PCI: hv: Only queue new work items in hv_pci_devices_present() if necessary

[Marcelo Henrique Cerri]

From: Dexuan Cui <decui at microsoft.com>

BugLink: http://bugs.launchpad.net/bugs/1758378

If there is pending work in hv_pci_devices_present() we just need to add
the new dr entry into the dr_list. Add a check to detect pending work
items and update the code to skip queuing work if pending work items
are detected.

Signed-off-by: Dexuan Cui <decui at microsoft.com>
[lorenzo.pieralisi at arm.com: updated commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
Reviewed-by: Michael Kelley <mikelley at microsoft.com>
Acked-by: Haiyang Zhang <haiyangz at microsoft.com>
Cc: Vitaly Kuznetsov <vkuznets at redhat.com>
Cc: Jack Morgenstein <jackm at mellanox.com>
Cc: Stephen Hemminger <sthemmin at microsoft.com>
Cc: K. Y. Srinivasan <kys at microsoft.com>
(cherry picked from commit 948373b3ed1bcf05a237c24675b84804315aff14)
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>
---
 drivers/pci/host/pci-hyperv.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/host/pci-hyperv.c b/drivers/pci/host/pci-hyperv.c
index 5eb7954ee584..f7d36c03486c 100644
--- a/drivers/pci/host/pci-hyperv.c
+++ b/drivers/pci/host/pci-hyperv.c
@@ -1801,6 +1801,7 @@ 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)
@@ -1824,11 +1825,21 @@ 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);
+	}
 }
 
 /**
-- 
2.17.1