-----Original Message----- From: Dexuan Cui Sent: Monday, March 5, 2018 11:22 AM To: bhelgaas@google.com; linux-pci@vger.kernel.org; KY Srinivasan kys@microsoft.com; Stephen Hemminger sthemmin@microsoft.com; olaf@aepfle.de; apw@canonical.com; jasowang@redhat.com Cc: linux-kernel@vger.kernel.org; driverdev-devel@linuxdriverproject.org; Haiyang Zhang haiyangz@microsoft.com; vkuznets@redhat.com; marcelo.cerri@canonical.com; Michael Kelley (EOSG) Michael.H.Kelley@microsoft.com; Dexuan Cui decui@microsoft.com; Jack Morgenstein jackm@mellanox.com; stable@vger.kernel.org Subject: [PATCH v2 5/6] PCI: hv: hv_pci_devices_present(): only queue a new work when necessary

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);

A minor point: The spin_unlock_irqrestore() call can stay here. Once we have the list status in a local variable and the new entry is added to the list, nothing bad can happen if we drop the spin lock. At worst, and very unlikely, we'll queue work when some other thread has already queued work to process the list entry, but that's no big deal. I'd argue for keeping the code covered by a spin lock as small as possible.

Michael

• 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