pci-hyper: Fix race condition bugs for fast device hotplug

---

v2:
Removed the "debug code".
No change to the patch body.
Added Cc:stable

v3:
Added Michael's Reviewed-by.

 drivers/pci/controller/pci-hyperv.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

drivers/pci/controller/pci-hyperv.c +13 -0

index f33370b756283..b82c7cde19e66 100644
@@ -3308,6 +3308,19 @@ static int hv_pci_query_relations(struct hv_device *hdev)
 	if (!ret)
 		ret = wait_for_response(hdev, &comp);
 
+	/*
+	 * In the case of fast device addition/removal, it's possible that
+	 * vmbus_sendpacket() or wait_for_response() returns -ENODEV but we
+	 * already got a PCI_BUS_RELATIONS* message from the host and the
+	 * channel callback already scheduled a work to hbus->wq, which can be
+	 * running survey_child_resources() -> complete(&hbus->survey_event),
+	 * even after hv_pci_query_relations() exits and the stack variable
+	 * 'comp' is no longer valid. This can cause a strange hang issue
+	 * or sometimes a page fault. Flush hbus->wq before we exit from
+	 * hv_pci_query_relations() to avoid the issues.
+	 */
+	flush_workqueue(hbus->wq);
+
 	return ret;
 }

Signature · 1 line

2.25.1

Lorenzo Pieralisi

maintainer Acked-by on v3 1/6

2023-05-25 08:14 UTC #2 lore raw

Re: [PATCH v3 1/6] PCI: hv: Fix a race condition bug in hv_pci_query_relations()

Quoted 3 lines · Dexuan Cui

Fix the longstanding race between hv_pci_query_relations() and survey_child_resources() by flushing the workqueue before we exit from hv_pci_query_relations().

"Fix the longstanding race" is vague. Please describe the race succinctly at least to give an idea of what the problem is.

Quoted 23 lines

Fixes 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs")
Signed-off-by Dexuan Cui <[email protected]>
Reviewed-by Michael Kelley <[email protected]>
Cc [email protected]
---
v2:
Removed the "debug code".
No change to the patch body.
Added Cc:stable
v3:
Added Michael's Reviewed-by.
 drivers/pci/controller/pci-hyperv.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)
drivers/pci/controller/pci-hyperv.c +0 -0
index f33370b756283..b82c7cde19e66 100644
@@ -3308,6 +3308,19 @@ static int hv_pci_query_relations(struct hv_device *hdev)
 	if (!ret)

drivers/pci/controller/pci-hyperv.c static int hv_pci_query_relations(struct hv_device *hdev) · line 3318

Quoted 10 lines

drivers/pci/controller/pci-hyperv.c +8 -0

 		ret = wait_for_response(hdev, &comp);
 
+	/*
+	 * In the case of fast device addition/removal, it's possible that
+	 * vmbus_sendpacket() or wait_for_response() returns -ENODEV but we
+	 * already got a PCI_BUS_RELATIONS* message from the host and the
+	 * channel callback already scheduled a work to hbus->wq, which can be
+	 * running survey_child_resources() -> complete(&hbus->survey_event),
+	 * even after hv_pci_query_relations() exits and the stack variable
+	 * 'comp' is no longer valid. This can cause a strange hang issue

"A strange hang" sounds like we don't understand what's happening, it does not feel like it is a solid understanding of the issue.

I would remove it - given that you already explain that comp is no longer valid - that is already a bug that needs fixing.

Acked-by Lorenzo Pieralisi <[email protected]>

Quoted 11 lines

drivers/pci/controller/pci-hyperv.c +5 -0

+	 * or sometimes a page fault. Flush hbus->wq before we exit from
+	 * hv_pci_query_relations() to avoid the issues.
+	 */
+	flush_workqueue(hbus->wq);
+
 	return ret;
 }

Signature · 1 line

2.25.1

Dexuan Cui

author maintainer

2023-06-15 03:55 UTC #3 lore raw

RE: [PATCH v3 1/6] PCI: hv: Fix a race condition bug in hv_pci_query_relations()

Quoted 11 lines

From: Lorenzo Pieralisi <[email protected]>
Sent: Thursday, May 25, 2023 1:14 AM
To: Dexuan Cui <[email protected]>
Quoted 3 lines · Dexuan Cui
Fix the longstanding race between hv_pci_query_relations() and survey_child_resources() by flushing the workqueue before we exit from hv_pci_query_relations().
"Fix the longstanding race" is vague. Please describe the race succinctly at least to give an idea of what the problem is.

Hi Lozenzo, I'm sorry for the late response -- finally I'm back on the patchset...

I'll use the below commit message in v4:

Since day 1 of the driver, there has been a race between hv_pci_query_relations() and survey_child_resources(): during fast device hotplug, hv_pci_query_relations() may error out due to device-remove and the stack variable 'comp' is no longer valid; however, pci_devices_present_work() -> survey_child_resources() -> complete() may be running on another CPU and accessing the no-longer-valid 'comp'. Fix the race by flushing the workqueue before we exit from hv_pci_query_relations().

I'll also update the comment to share more details of the race:

drivers/pci/controller/pci-hyperv.c +18 -0

@@ -3401,6 +3401,24 @@ static int hv_pci_query_relations(struct hv_device *hdev)
        if (!ret)
                ret = wait_for_response(hdev, &comp);
 
+       /*
+        * In the case of fast device addition/removal, it's possible that
+        * vmbus_sendpacket() or wait_for_response() returns -ENODEV but we
+        * already got a PCI_BUS_RELATIONS* message from the host and the
+        * channel callback already scheduled a work to hbus->wq, which can be
+        * running pci_devices_present_work() -> survey_child_resources() ->
+        * complete(&hbus->survey_event), even after hv_pci_query_relations()
+        * exits and the stack variable 'comp' is no longer valid; as a result,
+        * a hang or a page fault may happen when the complete() calls
+        * raw_spin_lock_irqsave(). Flush hbus->wq before we exit from
+        * hv_pci_query_relations() to avoid the issues. Note: if 'ret' is
+        * -ENODEV, there can't be any more work item scheduled to hbus->wq
+        * after the flush_workqueue(): see vmbus_onoffer_rescind() ->
+        * vmbus_reset_channel_cb(), vmbus_rescind_cleanup() ->
+        * channel->rescind = true.
+        */
+       flush_workqueue(hbus->wq);
+
        return ret;
 }

Quoted 12 lines

Review

Quoted 8 lines

(quoted diff) +7 -0

+	 * In the case of fast device addition/removal, it's possible that
+	 * vmbus_sendpacket() or wait_for_response() returns -ENODEV but we
+	 * already got a PCI_BUS_RELATIONS* message from the host and the
+	 * channel callback already scheduled a work to hbus->wq, which can
 be
+	 * running survey_child_resources() -> complete(&hbus->survey_event),
+	 * even after hv_pci_query_relations() exits and the stack variable
+	 * 'comp' is no longer valid. This can cause a strange hang issue

"A strange hang" sounds like we don't understand what's happening, it does not feel like it is a solid understanding of the issue.

Quoted 2 lines

I would remove it - given that you already explain that comp is no longer valid - that is already a bug that needs fixing.

I share more details in the comment (see the above).

Quoted 1 line

Acked-by Lorenzo Pieralisi <[email protected]>

Thanks!

Dexuan Cui

author maintainer

2023-04-20 02:41 UTC #4 lore raw

PATCH v3 2/6 PCI: hv: Fix a race condition in hv_irq_unmask() that can cause panic

When the host tries to remove a PCI device, the host first sends a PCI_EJECT message to the guest, and the guest is supposed to gracefully remove the PCI device and send a PCI_EJECTION_COMPLETE message to the host; the host then sends a VMBus message CHANNELMSG_RESCIND_CHANNELOFFER to the guest (when the guest receives this message, the device is already unassigned from the guest) and the guest can do some final cleanup work; if the guest fails to respond to the PCI_EJECT message within one minute, the host sends the VMBus message CHANNELMSG_RESCIND_CHANNELOFFER and removes the PCI device forcibly.

In the case of fast device addition/removal, it's possible that the PCI device driver is still configuring MSI-X interrupts when the guest receives the PCI_EJECT message; the channel callback calls hv_pci_eject_device(), which sets hpdev->state to hv_pcichild_ejecting, and schedules a work hv_eject_device_work(); if the PCI device driver is calling pci_alloc_irq_vectors() -> ... -> hv_compose_msi_msg(), we can break the while loop in hv_compose_msi_msg() due to the updated hpdev->state, and leave data->chip_data with its default value of NULL; later, when the PCI device driver calls request_irq() -> ... -> hv_irq_unmask(), the guest crashes in hv_arch_irq_unmask() due to data->chip_data being NULL.

Fix the issue by not testing hpdev->state in the while loop: when the guest receives PCI_EJECT, the device is still assigned to the guest, and the guest has one minute to finish the device removal gracefully. We don't really need to (and we should not) test hpdev->state in the loop.

Fixes de0aa7b2f97d ("PCI: hv: Fix 2 hang issues in hv_compose_msi_msg()")

Signed-off-by Dexuan Cui <[email protected]>

---

v2:
Removed the "debug code".
No change to the patch body.
Added Cc:stable

v3:
Added Michael's Reviewed-by.

 drivers/pci/controller/pci-hyperv.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

drivers/pci/controller/pci-hyperv.c +5 -6

index b82c7cde19e66..1b11cf7391933 100644
@@ -643,6 +643,11 @@ static void hv_arch_irq_unmask(struct irq_data *data)
 	pbus = pdev->bus;
 	hbus = container_of(pbus->sysdata, struct hv_pcibus_device, sysdata);
 	int_desc = data->chip_data;
+	if (!int_desc) {
+		dev_warn(&hbus->hdev->device, "%s() can not unmask irq %u\n",
+			 __func__, data->irq);
+		return;
+	}
 
 	spin_lock_irqsave(&hbus->retarget_msi_interrupt_lock, flags);

@@ -1911,12 +1916,6 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
 		hv_pci_onchannelcallback(hbus);
 		spin_unlock_irqrestore(&channel->sched_lock, flags);
 
-		if (hpdev->state == hv_pcichild_ejecting) {
-			dev_err_once(&hbus->hdev->device,
-				     "the device is being ejected\n");
-			goto enable_tasklet;
-		}
-
 		udelay(100);
 	}

Signature · 1 line

2.25.1

Lorenzo Pieralisi

maintainer

2023-05-25 10:16 UTC #5 lore raw

Re: [PATCH v3 2/6] PCI: hv: Fix a race condition in hv_irq_unmask() that can cause panic

Quoted 48 lines · Dexuan Cui

When the host tries to remove a PCI device, the host first sends a PCI_EJECT message to the guest, and the guest is supposed to gracefully remove the PCI device and send a PCI_EJECTION_COMPLETE message to the host; the host then sends a VMBus message CHANNELMSG_RESCIND_CHANNELOFFER to the guest (when the guest receives this message, the device is already unassigned from the guest) and the guest can do some final cleanup work; if the guest fails to respond to the PCI_EJECT message within one minute, the host sends the VMBus message CHANNELMSG_RESCIND_CHANNELOFFER and removes the PCI device forcibly.
In the case of fast device addition/removal, it's possible that the PCI device driver is still configuring MSI-X interrupts when the guest receives the PCI_EJECT message; the channel callback calls hv_pci_eject_device(), which sets hpdev->state to hv_pcichild_ejecting, and schedules a work hv_eject_device_work(); if the PCI device driver is calling pci_alloc_irq_vectors() -> ... -> hv_compose_msi_msg(), we can break the while loop in hv_compose_msi_msg() due to the updated hpdev->state, and leave data->chip_data with its default value of NULL; later, when the PCI device driver calls request_irq() -> ... -> hv_irq_unmask(), the guest crashes in hv_arch_irq_unmask() due to data->chip_data being NULL.
Fix the issue by not testing hpdev->state in the while loop: when the guest receives PCI_EJECT, the device is still assigned to the guest, and the guest has one minute to finish the device removal gracefully. We don't really need to (and we should not) test hpdev->state in the loop.
Fixes de0aa7b2f97d ("PCI: hv: Fix 2 hang issues in hv_compose_msi_msg()")
Signed-off-by Dexuan Cui <[email protected]>
Reviewed-by Michael Kelley <[email protected]>
Cc [email protected]
---
v2:
Removed the "debug code".
No change to the patch body.
Added Cc:stable
v3:
Added Michael's Reviewed-by.
 drivers/pci/controller/pci-hyperv.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)
drivers/pci/controller/pci-hyperv.c +0 -0
index b82c7cde19e66..1b11cf7391933 100644

drivers/pci/controller/pci-hyperv.c static void hv_arch_irq_unmask(struct irq_data *data) · line 650

Quoted 8 lines

drivers/pci/controller/pci-hyperv.c +5 -0

@@ -643,6 +643,11 @@ static void hv_arch_irq_unmask(struct irq_data *data)
 	pbus = pdev->bus;
 	hbus = container_of(pbus->sysdata, struct hv_pcibus_device, sysdata);
 	int_desc = data->chip_data;
+	if (!int_desc) {
+		dev_warn(&hbus->hdev->device, "%s() can not unmask irq %u\n",
+			 __func__, data->irq);
+		return;
+	}

That's a check that should be there regardless ?

Quoted 4 lines

drivers/pci/controller/pci-hyperv.c +0 -0

 	spin_lock_irqsave(&hbus->retarget_msi_interrupt_lock, flags);

@@ -1911,12 +1916,6 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
 		hv_pci_onchannelcallback(hbus);

drivers/pci/controller/pci-hyperv.c static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg) · line 1920

Quoted 10 lines

drivers/pci/controller/pci-hyperv.c +0 -6

 		spin_unlock_irqrestore(&channel->sched_lock, flags);
 
-		if (hpdev->state == hv_pcichild_ejecting) {
-			dev_err_once(&hbus->hdev->device,
-				     "the device is being ejected\n");
-			goto enable_tasklet;
-		}
-
 		udelay(100);
 	}

I don't understand why this code is in hv_compose_msi_msg() in the first place (and why only in that function ?) to me this looks like you are adding plasters in the code that can turn out to be problematic while ejecting a device, this does not seem robust at all - that's my opinion.

Feel free to merge this code, I can't ACK it, sorry.

Lorenzo

Dexuan Cui

author maintainer

2023-06-15 04:27 UTC #6 lore raw

RE: [PATCH v3 2/6] PCI: hv: Fix a race condition in hv_irq_unmask() that can cause panic

Quoted 16 lines

From: Lorenzo Pieralisi <[email protected]>
Sent: Thursday, May 25, 2023 3:16 AM
drivers/pci/controller/pci-hyperv.c static void hv_arch_irq_unmask(struct irq_data · line 651
Quoted 12 lines
drivers/pci/controller/pci-hyperv.c +5 -0
@@ -643,6 +643,11 @@ static void hv_arch_irq_unmask(struct irq_data
 *data)
 	pbus = pdev->bus;
 	hbus = container_of(pbus->sysdata, struct hv_pcibus_device, sysdata);
 	int_desc = data->chip_data;
+	if (!int_desc) {
+		dev_warn(&hbus->hdev->device, "%s() can not unmask irq %u\n",
+			 __func__, data->irq);
+		return;
+	}
That's a check that should be there regardless ?

Yes. Normally data->chip_data is set at the end of hv_compose_msi_msg(), and it should not be NULL. However, in rare circumstances, we might see a failure in hv_compose_msi_msg(), e.g. the hypervisor/host might return an error in comp.comp_pkt.completion_status (at least this is possible in theory).

In case we see a failure in hv_compose_msi_msg(), data->chip_data stays with its default value of NULL; because the return type of hv_compose_msi_msg() is "void", we can not return an error to the upper layer; later, when the upper layer calls request_irq() -> ... -> hv_irq_unmask(), hv_arch_irq_unmask() crashes because data->chip_data is NULL -- with this check, we're able to error out gracefully, and the user can better understand what goes wrong.

Quoted 7 lines

drivers/pci/controller/pci-hyperv.c static void hv_compose_msi_msg(struct
Quoted 3 lines
drivers/pci/controller/pci-hyperv.c +0 -0
 	spin_lock_irqsave(&hbus->retarget_msi_interrupt_lock, flags);
 
@@ -1911,12 +1916,6 @@ static void hv_compose_msi_msg(struct
irq_data *data, struct msi_msg *msg)
Quoted 3 lines
drivers/pci/controller/pci-hyperv.c +0 -0
 		hv_pci_onchannelcallback(hbus);
 		spin_unlock_irqrestore(&channel->sched_lock, flags);
 

Quoted 13 lines

drivers/pci/controller/pci-hyperv.c static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg) · line 1920
Quoted 8 lines
drivers/pci/controller/pci-hyperv.c +0 -6
-		if (hpdev->state == hv_pcichild_ejecting) {
-			dev_err_once(&hbus->hdev->device,
-				     "the device is being ejected\n");
-			goto enable_tasklet;
-		}
-
 		udelay(100);
 	}
I don't understand why this code is in hv_compose_msi_msg() in the first place (and why only in that function ?) to me this looks like you are adding plasters in the code that can turn out to be problematic while ejecting a device, this does not seem robust at all - that's my opinion.

The code was incorrectly added by
de0aa7b2f97d ("PCI: hv: Fix 2 hang issues in hv_compose_msi_msg()")

de0aa7b2f97d says

"
2. If the host is ejecting the VF device before we reach hv_compose_msi_msg(), in a UP VM, we can hang in hv_compose_msi_msg() forever, because at this time the host doesn't respond to the CREATE_INTERRUPT request.
"

de0aa7b2f97d implies that the host doesn't respond to the guest's CREATE_INTERRUPT request once the guest receives the PCI_EJECT message -- this is incorrect: after the guest receives the PCI_EJECT message, actually the host still responds to the guest's request, as long as the guest sends the request within 1 minute AND the guest doesn't send a PCI_EJECTION_COMPLETE message to the host in hv_eject_device_work(). The real issue is that currently the guest can send PCI_EJECTION_COMPLETE to the host before the guest finishes the device-probing/removing handling -- once the guest sends PCI_EJECTION_COMPLETE, the host unassigns the PCI device from the guest and ignores any request from the guest.

So here the check "hpdev->state == hv_pcichild_ejecting" is incorrect. We should remove the check since it can cause a panic (see the commit messsage for the detailed explanation)

The "premature PCI_EJECTION_COMPLETE" issue is resolved by:
[PATCH v3 5/6] PCI: hv: Add a per-bus mutex state_lock

Quoted 3 lines

Feel free to merge this code, I can't ACK it, sorry.
Lorenzo

Thanks for sharing the thougths!

Dexuan Cui

author maintainer

2023-04-20 02:41 UTC #7 lore raw

PATCH v3 3/6 PCI: hv: Remove the useless hv_pcichild_state from struct hv_pci_dev

The hpdev->state is never really useful. The only use in hv_pci_eject_device() and hv_eject_device_work() is not really necessary.

Signed-off-by Dexuan Cui <[email protected]>

---

v2:
No change to the patch body.
Added Cc:stable

v3:
Added Michael's Reviewed-by.

 drivers/pci/controller/pci-hyperv.c | 12 ------------
 1 file changed, 12 deletions(-)

drivers/pci/controller/pci-hyperv.c +0 ~~-12~~

index 1b11cf7391933..46df6d093d683 100644
@@ -553,19 +553,10 @@ struct hv_dr_state {
 	struct hv_pcidev_description func[];
 };
 
-enum hv_pcichild_state {
-	hv_pcichild_init = 0,
-	hv_pcichild_requirements,
-	hv_pcichild_resourced,
-	hv_pcichild_ejecting,
-	hv_pcichild_maximum
-};
-
 struct hv_pci_dev {
 	/* List protected by pci_rescan_remove_lock */
 	struct list_head list_entry;
 	refcount_t refs;
-	enum hv_pcichild_state state;
 	struct pci_slot *pci_slot;
 	struct hv_pcidev_description desc;
 	bool reported_missing;

@@ -2750,8 +2741,6 @@ static void hv_eject_device_work(struct work_struct *work)
 	hpdev = container_of(work, struct hv_pci_dev, wrk);
 	hbus = hpdev->hbus;
 
-	WARN_ON(hpdev->state != hv_pcichild_ejecting);
-
 	/*
 	 * Ejection can come before or after the PCI bus has been set up, so
 	 * attempt to find it and tear down the bus state, if it exists.  This

@@ -2808,7 +2797,6 @@ static void hv_pci_eject_device(struct hv_pci_dev *hpdev)
 		return;
 	}
 
-	hpdev->state = hv_pcichild_ejecting;
 	get_pcichild(hpdev);
 	INIT_WORK(&hpdev->wrk, hv_eject_device_work);
 	queue_work(hbus->wq, &hpdev->wrk);

Signature · 1 line

2.25.1

Lorenzo Pieralisi

maintainer Acked-by on v3 3/6

2023-05-25 08:16 UTC #8 lore raw

Re: [PATCH v3 3/6] PCI: hv: Remove the useless hv_pcichild_state from struct hv_pci_dev

Quoted 12 lines · Dexuan Cui

The hpdev->state is never really useful. The only use in hv_pci_eject_device() and hv_eject_device_work() is not really necessary.
Signed-off-by Dexuan Cui <[email protected]>
Reviewed-by Michael Kelley <[email protected]>
Cc [email protected]
---
v2:
No change to the patch body.
Added Cc:stable

Quoted 5 lines

v3:
Added Michael's Reviewed-by.

 drivers/pci/controller/pci-hyperv.c | 12 ------------
 1 file changed, 12 deletions(-)

Is this patch _required_ for subsequent fixes ? It is not a fix itself so I am asking.

Acked-by Lorenzo Pieralisi <[email protected]>

Quoted 44 lines

drivers/pci/controller/pci-hyperv.c +0 ~~-12~~

index 1b11cf7391933..46df6d093d683 100644
@@ -553,19 +553,10 @@ struct hv_dr_state {
 	struct hv_pcidev_description func[];
 };
 
-enum hv_pcichild_state {
-	hv_pcichild_init = 0,
-	hv_pcichild_requirements,
-	hv_pcichild_resourced,
-	hv_pcichild_ejecting,
-	hv_pcichild_maximum
-};
-
 struct hv_pci_dev {
 	/* List protected by pci_rescan_remove_lock */
 	struct list_head list_entry;
 	refcount_t refs;
-	enum hv_pcichild_state state;
 	struct pci_slot *pci_slot;
 	struct hv_pcidev_description desc;
 	bool reported_missing;

@@ -2750,8 +2741,6 @@ static void hv_eject_device_work(struct work_struct *work)
 	hpdev = container_of(work, struct hv_pci_dev, wrk);
 	hbus = hpdev->hbus;
 
-	WARN_ON(hpdev->state != hv_pcichild_ejecting);
-
 	/*
 	 * Ejection can come before or after the PCI bus has been set up, so
 	 * attempt to find it and tear down the bus state, if it exists.  This

@@ -2808,7 +2797,6 @@ static void hv_pci_eject_device(struct hv_pci_dev *hpdev)
 		return;
 	}
 
-	hpdev->state = hv_pcichild_ejecting;
 	get_pcichild(hpdev);
 	INIT_WORK(&hpdev->wrk, hv_eject_device_work);
 	queue_work(hbus->wq, &hpdev->wrk);

Signature · 1 line

2.25.1

Dexuan Cui

author maintainer

2023-06-15 04:36 UTC #9 lore raw

RE: [PATCH v3 3/6] PCI: hv: Remove the useless hv_pcichild_state from struct hv_pci_dev

Quoted 5 lines

From: Lorenzo Pieralisi <[email protected]>
Sent: Thursday, May 25, 2023 1:16 AM
To: Dexuan Cui <[email protected]>
Is this patch _required_ for subsequent fixes ?

It's not required. IMO it's good to have this patch with patch 2 since patch 2 also touches hv_pcichild_ejecting. I'm OK if people think it's better to merge this patch through the "next" branch rather than the "fixes" branch.

Quoted 3 lines

It is not a fix itself so I am asking.
Acked-by Lorenzo Pieralisi <[email protected]>

Thanks!

Dexuan Cui

author maintainer

2023-04-20 02:41 UTC #10 lore raw

PATCH v3 4/6 Revert "PCI: hv: Fix a timing issue which causes kdump to fail occasionally"

This reverts commit d6af2ed29c7c1c311b96dac989dcb991e90ee195.

The statement "the hv_pci_bus_exit() call releases structures of all its child devices" in commit d6af2ed29c7c is not true: in the path hv_pci_probe() -> hv_pci_enter_d0() -> hv_pci_bus_exit(hdev, true): the parameter "keep_devs" is true, so hv_pci_bus_exit() does *not* release the child "struct hv_pci_dev *hpdev" that is created earlier in pci_devices_present_work() -> new_pcichild_device().

The commit d6af2ed29c7c was originally made in July 2020 for RHEL 7.7, where the old version of hv_pci_bus_exit() was used; when the commit was rebased and merged into the upstream, people didn't notice that it's not really necessary. The commit itself doesn't cause any issue, but it makes hv_pci_probe() more complicated. Revert it to facilitate some upcoming changes to hv_pci_probe().

Signed-off-by Dexuan Cui <[email protected]>

Acked-by Wei Hu <[email protected]>

---

v2:
No change to the patch body.
Added Wei Hu's Acked-by.
Added Cc:stable

v3:
Added Michael's Reviewed-by.

 drivers/pci/controller/pci-hyperv.c | 71 ++++++++++++++---------------
 1 file changed, 34 insertions(+), 37 deletions(-)

drivers/pci/controller/pci-hyperv.c +34 ~~-37~~

index 46df6d093d683..48feab095a144 100644
@@ -3225,8 +3225,10 @@ static int hv_pci_enter_d0(struct hv_device *hdev)
 	struct pci_bus_d0_entry *d0_entry;
 	struct hv_pci_compl comp_pkt;
 	struct pci_packet *pkt;
+	bool retry = true;
 	int ret;
 
+enter_d0_retry:
 	/*
 	 * Tell the host that the bus is ready to use, and moved into the
 	 * powered-on state.  This includes telling the host which region

@@ -3253,6 +3255,38 @@ static int hv_pci_enter_d0(struct hv_device *hdev)
 	if (ret)
 		goto exit;
 
+	/*
+	 * In certain case (Kdump) the pci device of interest was
+	 * not cleanly shut down and resource is still held on host
+	 * side, the host could return invalid device status.
+	 * We need to explicitly request host to release the resource
+	 * and try to enter D0 again.
+	 */
+	if (comp_pkt.completion_status < 0 && retry) {
+		retry = false;
+
+		dev_err(&hdev->device, "Retrying D0 Entry\n");
+
+		/*
+		 * Hv_pci_bus_exit() calls hv_send_resource_released()
+		 * to free up resources of its child devices.
+		 * In the kdump kernel we need to set the
+		 * wslot_res_allocated to 255 so it scans all child
+		 * devices to release resources allocated in the
+		 * normal kernel before panic happened.
+		 */
+		hbus->wslot_res_allocated = 255;
+
+		ret = hv_pci_bus_exit(hdev, true);
+
+		if (ret == 0) {
+			kfree(pkt);
+			goto enter_d0_retry;
+		}
+		dev_err(&hdev->device,
+			"Retrying D0 failed with ret %d\n", ret);
+	}
+
 	if (comp_pkt.completion_status < 0) {
 		dev_err(&hdev->device,
 			"PCI Pass-through VSP failed D0 Entry with status %x\n",

@@ -3493,7 +3527,6 @@ static int hv_pci_probe(struct hv_device *hdev,
 	struct hv_pcibus_device *hbus;
 	u16 dom_req, dom;
 	char *name;
-	bool enter_d0_retry = true;
 	int ret;
 
 	/*

@@ -3633,47 +3666,11 @@ static int hv_pci_probe(struct hv_device *hdev,
 	if (ret)
 		goto free_fwnode;
 
-retry:
 	ret = hv_pci_query_relations(hdev);
 	if (ret)
 		goto free_irq_domain;
 
 	ret = hv_pci_enter_d0(hdev);
-	/*
-	 * In certain case (Kdump) the pci device of interest was
-	 * not cleanly shut down and resource is still held on host
-	 * side, the host could return invalid device status.
-	 * We need to explicitly request host to release the resource
-	 * and try to enter D0 again.
-	 * Since the hv_pci_bus_exit() call releases structures
-	 * of all its child devices, we need to start the retry from
-	 * hv_pci_query_relations() call, requesting host to send
-	 * the synchronous child device relations message before this
-	 * information is needed in hv_send_resources_allocated()
-	 * call later.
-	 */
-	if (ret == -EPROTO && enter_d0_retry) {
-		enter_d0_retry = false;
-
-		dev_err(&hdev->device, "Retrying D0 Entry\n");
-
-		/*
-		 * Hv_pci_bus_exit() calls hv_send_resources_released()
-		 * to free up resources of its child devices.
-		 * In the kdump kernel we need to set the
-		 * wslot_res_allocated to 255 so it scans all child
-		 * devices to release resources allocated in the
-		 * normal kernel before panic happened.
-		 */
-		hbus->wslot_res_allocated = 255;
-		ret = hv_pci_bus_exit(hdev, true);
-
-		if (ret == 0)
-			goto retry;
-
-		dev_err(&hdev->device,
-			"Retrying D0 failed with ret %d\n", ret);
-	}
 	if (ret)
 		goto free_irq_domain;

Signature · 1 line

2.25.1

Lorenzo Pieralisi

maintainer

2023-05-25 08:22 UTC #11 lore raw

Re: [PATCH v3 4/6] Revert "PCI: hv: Fix a timing issue which causes kdump to fail occasionally"

Quoted 9 lines · Dexuan Cui

This reverts commit d6af2ed29c7c1c311b96dac989dcb991e90ee195.
The statement "the hv_pci_bus_exit() call releases structures of all its child devices" in commit d6af2ed29c7c is not true: in the path hv_pci_probe() -> hv_pci_enter_d0() -> hv_pci_bus_exit(hdev, true): the parameter "keep_devs" is true, so hv_pci_bus_exit() does *not* release the child "struct hv_pci_dev *hpdev" that is created earlier in pci_devices_present_work() -> new_pcichild_device().

Quoted 6 lines

The commit d6af2ed29c7c was originally made in July 2020 for RHEL 7.7, where the old version of hv_pci_bus_exit() was used; when the commit was rebased and merged into the upstream, people didn't notice that it's not really necessary. The commit itself doesn't cause any issue, but it makes hv_pci_probe() more complicated. Revert it to facilitate some upcoming changes to hv_pci_probe().

If d6af2ed29c7c does not cause any issue this is not a fix and should be merged only with subsequent changes.

Quoted 130 lines

Signed-off-by Dexuan Cui <[email protected]>

Acked-by Wei Hu <[email protected]>

---

v2:
No change to the patch body.
Added Wei Hu's Acked-by.
Added Cc:stable

v3:
Added Michael's Reviewed-by.

 drivers/pci/controller/pci-hyperv.c | 71 ++++++++++++++---------------
 1 file changed, 34 insertions(+), 37 deletions(-)

drivers/pci/controller/pci-hyperv.c +34 ~~-37~~

index 46df6d093d683..48feab095a144 100644
@@ -3225,8 +3225,10 @@ static int hv_pci_enter_d0(struct hv_device *hdev)
 	struct pci_bus_d0_entry *d0_entry;
 	struct hv_pci_compl comp_pkt;
 	struct pci_packet *pkt;
+	bool retry = true;
 	int ret;
 
+enter_d0_retry:
 	/*
 	 * Tell the host that the bus is ready to use, and moved into the
 	 * powered-on state.  This includes telling the host which region

@@ -3253,6 +3255,38 @@ static int hv_pci_enter_d0(struct hv_device *hdev)
 	if (ret)
 		goto exit;
 
+	/*
+	 * In certain case (Kdump) the pci device of interest was
+	 * not cleanly shut down and resource is still held on host
+	 * side, the host could return invalid device status.
+	 * We need to explicitly request host to release the resource
+	 * and try to enter D0 again.
+	 */
+	if (comp_pkt.completion_status < 0 && retry) {
+		retry = false;
+
+		dev_err(&hdev->device, "Retrying D0 Entry\n");
+
+		/*
+		 * Hv_pci_bus_exit() calls hv_send_resource_released()
+		 * to free up resources of its child devices.
+		 * In the kdump kernel we need to set the
+		 * wslot_res_allocated to 255 so it scans all child
+		 * devices to release resources allocated in the
+		 * normal kernel before panic happened.
+		 */
+		hbus->wslot_res_allocated = 255;
+
+		ret = hv_pci_bus_exit(hdev, true);
+
+		if (ret == 0) {
+			kfree(pkt);
+			goto enter_d0_retry;
+		}
+		dev_err(&hdev->device,
+			"Retrying D0 failed with ret %d\n", ret);
+	}
+
 	if (comp_pkt.completion_status < 0) {
 		dev_err(&hdev->device,
 			"PCI Pass-through VSP failed D0 Entry with status %x\n",

@@ -3493,7 +3527,6 @@ static int hv_pci_probe(struct hv_device *hdev,
 	struct hv_pcibus_device *hbus;
 	u16 dom_req, dom;
 	char *name;
-	bool enter_d0_retry = true;
 	int ret;
 
 	/*

@@ -3633,47 +3666,11 @@ static int hv_pci_probe(struct hv_device *hdev,
 	if (ret)
 		goto free_fwnode;
 
-retry:
 	ret = hv_pci_query_relations(hdev);
 	if (ret)
 		goto free_irq_domain;
 
 	ret = hv_pci_enter_d0(hdev);
-	/*
-	 * In certain case (Kdump) the pci device of interest was
-	 * not cleanly shut down and resource is still held on host
-	 * side, the host could return invalid device status.
-	 * We need to explicitly request host to release the resource
-	 * and try to enter D0 again.
-	 * Since the hv_pci_bus_exit() call releases structures
-	 * of all its child devices, we need to start the retry from
-	 * hv_pci_query_relations() call, requesting host to send
-	 * the synchronous child device relations message before this
-	 * information is needed in hv_send_resources_allocated()
-	 * call later.
-	 */
-	if (ret == -EPROTO && enter_d0_retry) {
-		enter_d0_retry = false;
-
-		dev_err(&hdev->device, "Retrying D0 Entry\n");
-
-		/*
-		 * Hv_pci_bus_exit() calls hv_send_resources_released()
-		 * to free up resources of its child devices.
-		 * In the kdump kernel we need to set the
-		 * wslot_res_allocated to 255 so it scans all child
-		 * devices to release resources allocated in the
-		 * normal kernel before panic happened.
-		 */
-		hbus->wslot_res_allocated = 255;
-		ret = hv_pci_bus_exit(hdev, true);
-
-		if (ret == 0)
-			goto retry;
-
-		dev_err(&hdev->device,
-			"Retrying D0 failed with ret %d\n", ret);
-	}
 	if (ret)
 		goto free_irq_domain;

Signature · 1 line

2.25.1

Dexuan Cui

author maintainer

2023-06-15 04:42 UTC #12 lore raw

RE: [PATCH v3 4/6] Revert "PCI: hv: Fix a timing issue which causes kdump to fail occasionally"

Quoted 21 lines

From: Lorenzo Pieralisi <[email protected]>
Sent: Thursday, May 25, 2023 1:23 AM
...
Quoted 9 lines · Dexuan Cui
This reverts commit d6af2ed29c7c1c311b96dac989dcb991e90ee195.
The statement "the hv_pci_bus_exit() call releases structures of all its child devices" in commit d6af2ed29c7c is not true: in the path hv_pci_probe() -> hv_pci_enter_d0() -> hv_pci_bus_exit(hdev, true): the parameter "keep_devs" is true, so hv_pci_bus_exit() does *not* release the child "struct hv_pci_dev *hpdev" that is created earlier in pci_devices_present_work() -> new_pcichild_device().
Quoted 7 lines
The commit d6af2ed29c7c was originally made in July 2020 for RHEL 7.7, where the old version of hv_pci_bus_exit() was used; when the commit was
rebased and merged into the upstream, people didn't notice that it's not really necessary. The commit itself doesn't cause any issue, but it makes hv_pci_probe() more complicated. Revert it to facilitate some upcoming changes to hv_pci_probe().

Quoted 2 lines

If d6af2ed29c7c does not cause any issue this is not a fix and should be merged only with subsequent changes.

d6af2ed29c7c does not cause any functional issue, but it makes the code less readable, and so I'd like to not merge this patch with patch 5 -- this way people can easily know what the real change is in patch 5.

Dexuan Cui

author maintainer

2023-04-20 02:42 UTC #13 lore raw

PATCH v3 5/6 PCI: hv: Add a per-bus mutex state_lock

In the case of fast device addition/removal, it's possible that hv_eject_device_work() can start to run before create_root_hv_pci_bus() starts to run; as a result, the pci_get_domain_bus_and_slot() in hv_eject_device_work() can return a 'pdev' of NULL, and hv_eject_device_work() can remove the 'hpdev', and immediately send a message PCI_EJECTION_COMPLETE to the host, and the host immediately unassigns the PCI device from the guest; meanwhile, create_root_hv_pci_bus() and the PCI device driver can be probing the dead PCI device and reporting timeout errors.

Fix the issue by adding a per-bus mutex 'state_lock' and grabbing the mutex before powering on the PCI bus in hv_pci_enter_d0(): when hv_eject_device_work() starts to run, it's able to find the 'pdev' and call pci_stop_and_remove_bus_device(pdev): if the PCI device driver has loaded, the PCI device driver's probe() function is already called in create_root_hv_pci_bus() -> pci_bus_add_devices(), and now hv_eject_device_work() -> pci_stop_and_remove_bus_device() is able to call the PCI device driver's remove() function and remove the device reliably; if the PCI device driver hasn't loaded yet, the function call hv_eject_device_work() -> pci_stop_and_remove_bus_device() is able to remove the PCI device reliably and the PCI device driver's probe() function won't be called; if the PCI device driver's probe() is already running (e.g., systemd-udev is loading the PCI device driver), it must be holding the per-device lock, and after the probe() finishes and releases the lock, hv_eject_device_work() -> pci_stop_and_remove_bus_device() is able to proceed to remove the device reliably.

Fixes 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs")

Signed-off-by Dexuan Cui <[email protected]>

---

v2:
Removed the "debug code".
Fixed the "goto out" in hv_pci_resume() [Michael Kelley] Added Cc:stable

v3:
Added Michael's Reviewed-by.

 drivers/pci/controller/pci-hyperv.c | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

drivers/pci/controller/pci-hyperv.c +26 -3

index 48feab095a144..3ae2f99dea8c2 100644
@@ -489,7 +489,10 @@ struct hv_pcibus_device {
 	struct fwnode_handle *fwnode;
 	/* Protocol version negotiated with the host */
 	enum pci_protocol_version_t protocol_version;
+
+	struct mutex state_lock;
 	enum hv_pcibus_state state;
+
 	struct hv_device *hdev;
 	resource_size_t low_mmio_space;
 	resource_size_t high_mmio_space;

@@ -2512,6 +2515,8 @@ static void pci_devices_present_work(struct work_struct *work)
 	if (!dr)
 		return;
 
+	mutex_lock(&hbus->state_lock);
+
 	/* First, mark all existing children as reported missing. */
 	spin_lock_irqsave(&hbus->device_list_lock, flags);
 	list_for_each_entry(hpdev, &hbus->children, list_entry) {

@@ -2593,6 +2598,8 @@ static void pci_devices_present_work(struct work_struct *work)
 		break;
 	}
 
+	mutex_unlock(&hbus->state_lock);
+
 	kfree(dr);
 }

@@ -2741,6 +2748,8 @@ static void hv_eject_device_work(struct work_struct *work)
 	hpdev = container_of(work, struct hv_pci_dev, wrk);
 	hbus = hpdev->hbus;
 
+	mutex_lock(&hbus->state_lock);
+
 	/*
 	 * Ejection can come before or after the PCI bus has been set up, so
 	 * attempt to find it and tear down the bus state, if it exists.  This

@@ -2777,6 +2786,8 @@ static void hv_eject_device_work(struct work_struct *work)
 	put_pcichild(hpdev);
 	put_pcichild(hpdev);
 	/* hpdev has been freed. Do not use it any more. */
+
+	mutex_unlock(&hbus->state_lock);
 }
 
 /**

@@ -3562,6 +3573,7 @@ static int hv_pci_probe(struct hv_device *hdev,
 		return -ENOMEM;
 
 	hbus->bridge = bridge;
+	mutex_init(&hbus->state_lock);
 	hbus->state = hv_pcibus_init;
 	hbus->wslot_res_allocated = -1;

@@ -3670,9 +3682,11 @@ static int hv_pci_probe(struct hv_device *hdev,
 	if (ret)
 		goto free_irq_domain;
 
+	mutex_lock(&hbus->state_lock);
+
 	ret = hv_pci_enter_d0(hdev);
 	if (ret)
-		goto free_irq_domain;
+		goto release_state_lock;
 
 	ret = hv_pci_allocate_bridge_windows(hbus);
 	if (ret)

@@ -3690,12 +3704,15 @@ static int hv_pci_probe(struct hv_device *hdev,
 	if (ret)
 		goto free_windows;
 
+	mutex_unlock(&hbus->state_lock);
 	return 0;
 
 free_windows:
 	hv_pci_free_bridge_windows(hbus);
 exit_d0:
 	(void) hv_pci_bus_exit(hdev, true);
+release_state_lock:
+	mutex_unlock(&hbus->state_lock);
 free_irq_domain:
 	irq_domain_remove(hbus->irq_domain);
 free_fwnode:

@@ -3945,20 +3962,26 @@ static int hv_pci_resume(struct hv_device *hdev)
 	if (ret)
 		goto out;
 
+	mutex_lock(&hbus->state_lock);
+
 	ret = hv_pci_enter_d0(hdev);
 	if (ret)
-		goto out;
+		goto release_state_lock;
 
 	ret = hv_send_resources_allocated(hdev);
 	if (ret)
-		goto out;
+		goto release_state_lock;
 
 	prepopulate_bars(hbus);
 
 	hv_pci_restore_msi_state(hbus);
 
 	hbus->state = hv_pcibus_installed;
+	mutex_unlock(&hbus->state_lock);
 	return 0;
+
+release_state_lock:
+	mutex_unlock(&hbus->state_lock);
 out:
 	vmbus_close(hdev->channel);
 	return ret;

Signature · 1 line

2.25.1

Lorenzo Pieralisi

maintainer Acked-by on v3 5/6

2023-05-25 08:27 UTC #14 lore raw

Re: [PATCH v3 5/6] PCI: hv: Add a per-bus mutex state_lock

Quoted 38 lines · Dexuan Cui

In the case of fast device addition/removal, it's possible that hv_eject_device_work() can start to run before create_root_hv_pci_bus() starts to run; as a result, the pci_get_domain_bus_and_slot() in hv_eject_device_work() can return a 'pdev' of NULL, and hv_eject_device_work() can remove the 'hpdev', and immediately send a message PCI_EJECTION_COMPLETE to the host, and the host immediately unassigns the PCI device from the guest; meanwhile, create_root_hv_pci_bus() and the PCI device driver can be probing the dead PCI device and reporting timeout errors.
Fix the issue by adding a per-bus mutex 'state_lock' and grabbing the mutex before powering on the PCI bus in hv_pci_enter_d0(): when hv_eject_device_work() starts to run, it's able to find the 'pdev' and call pci_stop_and_remove_bus_device(pdev): if the PCI device driver has loaded, the PCI device driver's probe() function is already called in create_root_hv_pci_bus() -> pci_bus_add_devices(), and now hv_eject_device_work() -> pci_stop_and_remove_bus_device() is able to call the PCI device driver's remove() function and remove the device reliably; if the PCI device driver hasn't loaded yet, the function call hv_eject_device_work() -> pci_stop_and_remove_bus_device() is able to remove the PCI device reliably and the PCI device driver's probe() function won't be called; if the PCI device driver's probe() is already running (e.g., systemd-udev is loading the PCI device driver), it must be holding the per-device lock, and after the probe() finishes and releases the lock, hv_eject_device_work() -> pci_stop_and_remove_bus_device() is able to proceed to remove the device reliably.
Fixes 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs")
Signed-off-by Dexuan Cui <[email protected]>
Reviewed-by Michael Kelley <[email protected]>
Cc [email protected]
---
v2:
Removed the "debug code".
Fixed the "goto out" in hv_pci_resume() [Michael Kelley] Added Cc:stable

Quoted 5 lines

v3:
Added Michael's Reviewed-by.

 drivers/pci/controller/pci-hyperv.c | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

Acked-by Lorenzo Pieralisi <[email protected]>

Quoted 120 lines

drivers/pci/controller/pci-hyperv.c +26 -3

index 48feab095a144..3ae2f99dea8c2 100644
@@ -489,7 +489,10 @@ struct hv_pcibus_device {
 	struct fwnode_handle *fwnode;
 	/* Protocol version negotiated with the host */
 	enum pci_protocol_version_t protocol_version;
+
+	struct mutex state_lock;
 	enum hv_pcibus_state state;
+
 	struct hv_device *hdev;
 	resource_size_t low_mmio_space;
 	resource_size_t high_mmio_space;

@@ -2512,6 +2515,8 @@ static void pci_devices_present_work(struct work_struct *work)
 	if (!dr)
 		return;
 
+	mutex_lock(&hbus->state_lock);
+
 	/* First, mark all existing children as reported missing. */
 	spin_lock_irqsave(&hbus->device_list_lock, flags);
 	list_for_each_entry(hpdev, &hbus->children, list_entry) {

@@ -2593,6 +2598,8 @@ static void pci_devices_present_work(struct work_struct *work)
 		break;
 	}
 
+	mutex_unlock(&hbus->state_lock);
+
 	kfree(dr);
 }

@@ -2741,6 +2748,8 @@ static void hv_eject_device_work(struct work_struct *work)
 	hpdev = container_of(work, struct hv_pci_dev, wrk);
 	hbus = hpdev->hbus;
 
+	mutex_lock(&hbus->state_lock);
+
 	/*
 	 * Ejection can come before or after the PCI bus has been set up, so
 	 * attempt to find it and tear down the bus state, if it exists.  This

@@ -2777,6 +2786,8 @@ static void hv_eject_device_work(struct work_struct *work)
 	put_pcichild(hpdev);
 	put_pcichild(hpdev);
 	/* hpdev has been freed. Do not use it any more. */
+
+	mutex_unlock(&hbus->state_lock);
 }
 
 /**

@@ -3562,6 +3573,7 @@ static int hv_pci_probe(struct hv_device *hdev,
 		return -ENOMEM;
 
 	hbus->bridge = bridge;
+	mutex_init(&hbus->state_lock);
 	hbus->state = hv_pcibus_init;
 	hbus->wslot_res_allocated = -1;

@@ -3670,9 +3682,11 @@ static int hv_pci_probe(struct hv_device *hdev,
 	if (ret)
 		goto free_irq_domain;
 
+	mutex_lock(&hbus->state_lock);
+
 	ret = hv_pci_enter_d0(hdev);
 	if (ret)
-		goto free_irq_domain;
+		goto release_state_lock;
 
 	ret = hv_pci_allocate_bridge_windows(hbus);
 	if (ret)

@@ -3690,12 +3704,15 @@ static int hv_pci_probe(struct hv_device *hdev,
 	if (ret)
 		goto free_windows;
 
+	mutex_unlock(&hbus->state_lock);
 	return 0;
 
 free_windows:
 	hv_pci_free_bridge_windows(hbus);
 exit_d0:
 	(void) hv_pci_bus_exit(hdev, true);
+release_state_lock:
+	mutex_unlock(&hbus->state_lock);
 free_irq_domain:
 	irq_domain_remove(hbus->irq_domain);
 free_fwnode:

@@ -3945,20 +3962,26 @@ static int hv_pci_resume(struct hv_device *hdev)
 	if (ret)
 		goto out;
 
+	mutex_lock(&hbus->state_lock);
+
 	ret = hv_pci_enter_d0(hdev);
 	if (ret)
-		goto out;
+		goto release_state_lock;
 
 	ret = hv_send_resources_allocated(hdev);
 	if (ret)
-		goto out;
+		goto release_state_lock;
 
 	prepopulate_bars(hbus);
 
 	hv_pci_restore_msi_state(hbus);
 
 	hbus->state = hv_pcibus_installed;
+	mutex_unlock(&hbus->state_lock);
 	return 0;
+
+release_state_lock:
+	mutex_unlock(&hbus->state_lock);
 out:
 	vmbus_close(hdev->channel);
 	return ret;

Signature · 1 line

2.25.1

Dexuan Cui

author maintainer

2023-04-20 02:42 UTC #15 lore raw

PATCH v3 6/6 PCI: hv: Use async probing to reduce boot time

Commit 414428c5da1c ("PCI: hv: Lock PCI bus on device eject") added pci_lock_rescan_remove() and pci_unlock_rescan_remove() in create_root_hv_pci_bus() and in hv_eject_device_work() to address the race between create_root_hv_pci_bus() and hv_eject_device_work(), but it turns that grabing the pci_rescan_remove_lock mutex is not enough:
refer to the earlier fix "PCI: hv: Add a per-bus mutex state_lock".

Now with hbus->state_lock and other fixes, the race is resolved, so remove pci_{lock,unlock}_rescan_remove() in create_root_hv_pci_bus():
this removes the serialization in hv_pci_probe() and hence allows async-probing (PROBE_PREFER_ASYNCHRONOUS) to work.

Add the async-probing flag to hv_pci_drv.

pci_{lock,unlock}_rescan_remove() in hv_eject_device_work() and in hv_pci_remove() are still kept: according to the comment before drivers/pci/probe.c: static DEFINE_MUTEX(pci_rescan_remove_lock), "PCI device removal routines should always be executed under this mutex".

Signed-off-by Dexuan Cui <[email protected]>

Reviewed-by Long Li <[email protected]>

---

v2:
No change to the patch body.
Improved the commit message [Michael Kelley]
Added Cc:stable

v3:
Added Michael's and Long Li's Reviewed-by.
Fixed a typo in the commit message: grubing -> grabing [Thanks, Michael!]

 drivers/pci/controller/pci-hyperv.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

drivers/pci/controller/pci-hyperv.c +9 -2

index 3ae2f99dea8c2..2ea2b1b8a4c9a 100644
@@ -2312,12 +2312,16 @@ static int create_root_hv_pci_bus(struct hv_pcibus_device *hbus)
 	if (error)
 		return error;
 
-	pci_lock_rescan_remove();
+	/*
+	 * pci_lock_rescan_remove() and pci_unlock_rescan_remove() are
+	 * unnecessary here, because we hold the hbus->state_lock, meaning
+	 * hv_eject_device_work() and pci_devices_present_work() can't race
+	 * with create_root_hv_pci_bus().
+	 */
 	hv_pci_assign_numa_node(hbus);
 	pci_bus_assign_resources(bridge->bus);
 	hv_pci_assign_slots(hbus);
 	pci_bus_add_devices(bridge->bus);
-	pci_unlock_rescan_remove();
 	hbus->state = hv_pcibus_installed;
 	return 0;
 }

@@ -4003,6 +4007,9 @@ static struct hv_driver hv_pci_drv = {
 	.remove		= hv_pci_remove,
 	.suspend	= hv_pci_suspend,
 	.resume		= hv_pci_resume,
+	.driver = {
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
 };
 
 static void __exit exit_hv_pci_drv(void)

Signature · 1 line

2.25.1

Simon Horman

2023-04-23 19:11 UTC #16 lore raw

Re: [PATCH v3 6/6] PCI: hv: Use async probing to reduce boot time

Quoted 5 lines · Dexuan Cui

Commit 414428c5da1c ("PCI: hv: Lock PCI bus on device eject") added pci_lock_rescan_remove() and pci_unlock_rescan_remove() in create_root_hv_pci_bus() and in hv_eject_device_work() to address the race between create_root_hv_pci_bus() and hv_eject_device_work(), but it turns that grabing the pci_rescan_remove_lock mutex is not enough:

nit: s/grabing/grabbing/g

Quoted 1 line

refer to the earlier fix "PCI: hv: Add a per-bus mutex state_lock".

...

Dexuan Cui

author maintainer

2023-04-24 20:50 UTC #17 lore raw

RE: [PATCH v3 6/6] PCI: hv: Use async probing to reduce boot time

Quoted 5 lines

From: Simon Horman <[email protected]>
Sent: Sunday, April 23, 2023 12:11 PM
To: Dexuan Cui <[email protected]>
...
On Wed, Apr 19, 2023 at 07:40:37PM -0700, Dexuan Cui wrote:

Quoted 7 lines

Quoted 5 lines
Commit 414428c5da1c ("PCI: hv: Lock PCI bus on device eject") added pci_lock_rescan_remove() and pci_unlock_rescan_remove() in create_root_hv_pci_bus() and in hv_eject_device_work() to address the race between create_root_hv_pci_bus() and hv_eject_device_work(), but it turns that grabing the pci_rescan_remove_lock mutex is not enough:
nit: s/grabing/grabbing/g

Thanks for spotting this! I suppose the maintainer(s) would help fix this.

Lorenzo Pieralisi

maintainer

2023-05-10 08:23 UTC #18 lore raw

Re: [PATCH v3 6/6] PCI: hv: Use async probing to reduce boot time

Quoted 6 lines · Dexuan Cui

Commit 414428c5da1c ("PCI: hv: Lock PCI bus on device eject") added pci_lock_rescan_remove() and pci_unlock_rescan_remove() in create_root_hv_pci_bus() and in hv_eject_device_work() to address the race between create_root_hv_pci_bus() and hv_eject_device_work(), but it turns that grabing the pci_rescan_remove_lock mutex is not enough:
refer to the earlier fix "PCI: hv: Add a per-bus mutex state_lock".

This is meaningless for a commit log reader, there is nothing to refer to.

Quoted 1 line

Now with hbus->state_lock and other fixes, the race is resolved, so

"other fixes" is meaningless too.

Explain the problem and how you fix it (this patch should be split because the Subject does not represent what you are doing precisely, see below).

Quoted 5 lines

remove pci_{lock,unlock}_rescan_remove() in create_root_hv_pci_bus():
this removes the serialization in hv_pci_probe() and hence allows async-probing (PROBE_PREFER_ASYNCHRONOUS) to work.
Add the async-probing flag to hv_pci_drv.

Adding the asynchronous probing should be a separate patch and I don't think you should send it to stable kernels straight away because a) it is not a fix b) it can trigger further regressions.

Quoted 4 lines

pci_{lock,unlock}_rescan_remove() in hv_eject_device_work() and in hv_pci_remove() are still kept: according to the comment before drivers/pci/probe.c: static DEFINE_MUTEX(pci_rescan_remove_lock), "PCI device removal routines should always be executed under this mutex".

This patch should be split, first thing is to fix and document what you are changing for pci_{lock,unlock}_rescan_remove() then add asynchronous probing.

Lorenzo

Quoted 54 lines

Signed-off-by Dexuan Cui <[email protected]>

Reviewed-by Long Li <[email protected]>

---

v2:
No change to the patch body.
Improved the commit message [Michael Kelley]
Added Cc:stable

v3:
Added Michael's and Long Li's Reviewed-by.
Fixed a typo in the commit message: grubing -> grabing [Thanks, Michael!]

 drivers/pci/controller/pci-hyperv.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

drivers/pci/controller/pci-hyperv.c +9 -2

index 3ae2f99dea8c2..2ea2b1b8a4c9a 100644
@@ -2312,12 +2312,16 @@ static int create_root_hv_pci_bus(struct hv_pcibus_device *hbus)
 	if (error)
 		return error;
 
-	pci_lock_rescan_remove();
+	/*
+	 * pci_lock_rescan_remove() and pci_unlock_rescan_remove() are
+	 * unnecessary here, because we hold the hbus->state_lock, meaning
+	 * hv_eject_device_work() and pci_devices_present_work() can't race
+	 * with create_root_hv_pci_bus().
+	 */
 	hv_pci_assign_numa_node(hbus);
 	pci_bus_assign_resources(bridge->bus);
 	hv_pci_assign_slots(hbus);
 	pci_bus_add_devices(bridge->bus);
-	pci_unlock_rescan_remove();
 	hbus->state = hv_pcibus_installed;
 	return 0;
 }

@@ -4003,6 +4007,9 @@ static struct hv_driver hv_pci_drv = {
 	.remove		= hv_pci_remove,
 	.suspend	= hv_pci_suspend,
 	.resume		= hv_pci_resume,
+	.driver = {
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
 };
 
 static void __exit exit_hv_pci_drv(void)

Signature · 1 line

2.25.1

Dexuan Cui

author maintainer

2023-05-10 17:12 UTC #19 lore raw

RE: [PATCH v3 6/6] PCI: hv: Use async probing to reduce boot time

Quoted 12 lines

From: Lorenzo Pieralisi <[email protected]>
Sent: Wednesday, May 10, 2023 1:23 AM
To: Dexuan Cui <[email protected]>
...
Quoted 6 lines · Dexuan Cui
Commit 414428c5da1c ("PCI: hv: Lock PCI bus on device eject") added pci_lock_rescan_remove() and pci_unlock_rescan_remove() in create_root_hv_pci_bus() and in hv_eject_device_work() to address the race between create_root_hv_pci_bus() and hv_eject_device_work(), but it turns that grabing the pci_rescan_remove_lock mutex is not enough:
refer to the earlier fix "PCI: hv: Add a per-bus mutex state_lock".

Quoted 2 lines

This is meaningless for a commit log reader, there is nothing to refer to.

Correct. Because patch 5
[PATCH v3 5/6] PCI: hv: Add a per-bus mutex state_lock has not been in any upstream tree, so I don't have a commit id yet.

Quoted 3 lines

Quoted 1 line
Now with hbus->state_lock and other fixes, the race is resolved, so
"other fixes" is meaningless too.

Ditto.

Quoted 3 lines

Explain the problem and how you fix it (this patch should be split because the Subject does not represent what you are doing precisely, see below).

Ok, I will better explain the boot time issue.

Quoted 9 lines

Quoted 5 lines
remove pci_{lock,unlock}_rescan_remove() in create_root_hv_pci_bus():
this removes the serialization in hv_pci_probe() and hence allows async-probing (PROBE_PREFER_ASYNCHRONOUS) to work.
Add the async-probing flag to hv_pci_drv.
Adding the asynchronous probing should be a separate patch and I don't think you should send it to stable kernels straight away because a) it is not a fix b) it can trigger further regressions.

Agreed. I'll remove the line "Cc: stable".

Quoted 10 lines

Quoted 4 lines
pci_{lock,unlock}_rescan_remove() in hv_eject_device_work() and in hv_pci_remove() are still kept: according to the comment before drivers/pci/probe.c: static DEFINE_MUTEX(pci_rescan_remove_lock), "PCI device removal routines should always be executed under this mutex".
This patch should be split, first thing is to fix and document what you are changing for pci_{lock,unlock}_rescan_remove() then add asynchronous probing.
Lorenzo

Ok, I'll split this patch into two.

Thanks for reviewing the patch.
Can you please give an "Acked-by" or "Reviewed-by" to patch 1~5 if they look good to you? The first 5 patches have been there for a while, and they already got Michael's Reviewed-by.

I hope the first 5 patches can go through the hyperv-fixes branch in the hyperv tree
https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git/log/?h=hyperv-fixes
since they are specific to Hyper-V.

After the first 5 patches are in, I can refer to the commit IDs, and I will split this patch (patch 6).

Thanks,
Dexuan

Dexuan Cui

author maintainer

2023-05-17 00:03 UTC #20 lore raw

RE: [PATCH v3 6/6] PCI: hv: Use async probing to reduce boot time

Quoted 8 lines

From: Dexuan Cui
Sent: Wednesday, May 10, 2023 10:12 AM
To: Lorenzo Pieralisi <[email protected]>
Quoted 5 lines
...
This patch should be split, first thing is to fix and document what you are changing for pci_{lock,unlock}_rescan_remove() then add asynchronous probing.

Quoted 7 lines

Quoted 1 line
Lorenzo
Ok, I'll split this patch into two.
Thanks for reviewing the patch.
Can you please give an "Acked-by" or "Reviewed-by" to patch 1~5 if they look good to you? The first 5 patches have been there for a while, and they already got Michael's Reviewed-by.

Hi Lorenzo, Bjorn and all,
Ping -- it would be great to have your Acked-by or Reviewed-by for patch 1 to 5.

Quoted 11 lines

I hope the first 5 patches can go through the hyperv-fixes branch in the hyperv tree
https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git/log/?h=hyp
erv-fixes
since they are specific to Hyper-V.
After the first 5 patches are in, I can refer to the commit IDs, and I will split this patch (patch 6).
Thanks,
Dexuan

Dexuan Cui

author maintainer

2023-05-23 19:30 UTC #21 lore raw

RE: [PATCH v3 6/6] PCI: hv: Use async probing to reduce boot time

Quoted 14 lines

From: Dexuan Cui <[email protected]>
Sent: Tuesday, May 16, 2023 5:03 PM
...
Quoted 11 lines
From: Dexuan Cui
Sent: Wednesday, May 10, 2023 10:12 AM
To: Lorenzo Pieralisi <[email protected]>
Quoted 6 lines
...
This patch should be split, first thing is to fix and document what you are changing for pci_{lock,unlock}_rescan_remove() then add asynchronous probing.
Lorenzo
Ok, I'll split this patch into two.

Quoted 8 lines

Quoted 4 lines
Thanks for reviewing the patch.
Can you please give an "Acked-by" or "Reviewed-by" to patch 1~5 if they look good to you? The first 5 patches have been there for a while, and they already got Michael's Reviewed-by.
Hi Lorenzo, Bjorn and all,
Ping -- it would be great to have your Acked-by or Reviewed-by for patch 1 to 5.

Gentle ping .

Quoted 19 lines

Quoted 3 lines
I hope the first 5 patches can go through the hyperv-fixes branch in the hyperv tree
https://git.ke/
rnel.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Fhyperv%2Flinux.git%2F log%2F%3Fh%3Dhyp&data=05%7C01%7Cdecui%40microsoft.com%7C65c86f fe8d8542dbae0708db566a1607%7C72f988bf86f141af91ab2d7cd011db47% 7C1%7C0%7C638198785892993948%7CUnknown%7CTWFpbGZsb3d8eyJWIj oiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3 000%7C%7C%7C&sdata=h9vxjnGo6oYzare%2FqqcXndg2NZZ0Ap%2BH33q0i Mtf7D4%3D&reserved=0
Quoted 8 lines
erv-fixes
since they are specific to Hyper-V.
After the first 5 patches are in, I can refer to the commit IDs, and I will split this patch (patch 6).
Thanks,
Dexuan

Dexuan Cui

author maintainer

2023-04-21 02:04 UTC #22 lore raw