linux-kernel - [PATCH] PCI: hv: Fix a bug on removing child devices on the bus

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Message-Id: <1629789620-11049-1-git-send-email-longli@linuxonhyperv.com>
Date:   Tue, 24 Aug 2021 00:20:20 -0700
From:   longli@...uxonhyperv.com
To:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org
Cc:     Long Li <longli@...rosoft.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: [PATCH] PCI: hv: Fix a bug on removing child devices on the bus

From: Long Li <longli@...rosoft.com>

In hv_pci_bus_exit, the code is holding a spinlock while calling
pci_destroy_slot(), which takes a mutex.

This is not safe for spinlock. Fix this by moving the children to be
deleted to a list on the stack, and removing them after spinlock is
released.

Fixes: 94d22763207a ("PCI: hv: Fix a race condition when removing the device")

Cc: "K. Y. Srinivasan" <kys@...rosoft.com>
Cc: Haiyang Zhang <haiyangz@...rosoft.com>
Cc: Stephen Hemminger <sthemmin@...rosoft.com>
Cc: Wei Liu <wei.liu@...nel.org>
Cc: Dexuan Cui <decui@...rosoft.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc: Rob Herring <robh@...nel.org>
Cc: "Krzysztof Wilczyński" <kw@...ux.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Michael Kelley <mikelley@...rosoft.com>
Cc: Dan Carpenter <dan.carpenter@...cle.com>
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Long Li <longli@...rosoft.com>
---
 drivers/pci/controller/pci-hyperv.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index a53bd8728d0d..d4f3cce18957 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -3220,6 +3220,7 @@ static int hv_pci_bus_exit(struct hv_device *hdev, bool keep_devs)
 	struct hv_pci_dev *hpdev, *tmp;
 	unsigned long flags;
 	int ret;
+	struct list_head removed;
 
 	/*
 	 * After the host sends the RESCIND_CHANNEL message, it doesn't
@@ -3229,9 +3230,18 @@ static int hv_pci_bus_exit(struct hv_device *hdev, bool keep_devs)
 		return 0;
 
 	if (!keep_devs) {
-		/* Delete any children which might still exist. */
+		INIT_LIST_HEAD(&removed);
+
+		/* Move all present children to the list on stack */
 		spin_lock_irqsave(&hbus->device_list_lock, flags);
-		list_for_each_entry_safe(hpdev, tmp, &hbus->children, list_entry) {
+		list_for_each_entry_safe(hpdev, tmp, &hbus->children, list_entry)
+			list_move_tail(&hpdev->list_entry, &removed);
+		spin_unlock_irqrestore(&hbus->device_list_lock, flags);
+
+		/* Remove all children in the list */
+		while (!list_empty(&removed)) {
+			hpdev = list_first_entry(&removed, struct hv_pci_dev,
+						 list_entry);
 			list_del(&hpdev->list_entry);
 			if (hpdev->pci_slot)
 				pci_destroy_slot(hpdev->pci_slot);
@@ -3239,7 +3249,6 @@ static int hv_pci_bus_exit(struct hv_device *hdev, bool keep_devs)
 			put_pcichild(hpdev);
 			put_pcichild(hpdev);
 		}
-		spin_unlock_irqrestore(&hbus->device_list_lock, flags);
 	}
 
 	ret = hv_send_resources_released(hdev);
-- 
2.25.1