linux-kernel - [PATCH 1/3] PCI: hv: Fix a memory leak in hv_eject_device

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Date:   Mon, 4 Mar 2019 21:34:48 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
CC:     "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "driverdev-devel@...uxdriverproject.org" 
        <driverdev-devel@...uxdriverproject.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "apw@...onical.com" <apw@...onical.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        vkuznets <vkuznets@...hat.com>,
        "marcelo.cerri@...onical.com" <marcelo.cerri@...onical.com>,
        "jackm@...lanox.com" <jackm@...lanox.com>,
        Dexuan Cui <decui@...rosoft.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: [PATCH 1/3] PCI: hv: Fix a memory leak in hv_eject_device_work()

After a device is just created in new_pcichild_device(), hpdev->refs is set
to 2 (i.e. the initial value of 1 plus the get_pcichild()).

When we hot remove the device from the host, in Linux VM we first call
hv_pci_eject_device(), which increases hpdev->refs by get_pcichild() and
then schedules a work of hv_eject_device_work(), so hpdev->refs becomes 3
(let's ignore the paired get/put_pcichild() in other places). But in
hv_eject_device_work(), currently we only call put_pcichild() twice,
meaning the 'hpdev' struct can't be freed in put_pcichild(). This patch
adds one put_pcichild() to fix the memory leak.

BTW, the device can also be removed when we run "rmmod pci-hyperv". On this
path (hv_pci_remove() -> hv_pci_bus_exit() -> hv_pci_devices_present()),
hpdev->refs is 2, and we do correctly call put_pcichild() twice in
pci_devices_present_work().

Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs")
Signed-off-by: Dexuan Cui <decui@...rosoft.com>
Cc: <stable@...r.kernel.org>
---
 drivers/pci/controller/pci-hyperv.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index 95441a35eceb..30f16b882746 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -1900,6 +1900,9 @@ static void hv_eject_device_work(struct work_struct *work)
 			 sizeof(*ejct_pkt), (unsigned long)&ctxt.pkt,
 			 VM_PKT_DATA_INBAND, 0);
 
+	/* For the get_pcichild() in hv_pci_eject_device() */
+	put_pcichild(hpdev);
+	/* For the two refs got in new_pcichild_device() */
 	put_pcichild(hpdev);
 	put_pcichild(hpdev);
 	put_hvpcibus(hpdev->hbus);
-- 
2.19.1