Patch "PCI: hv: Fix a race condition bug in hv_pci_query_relations()" has been added to the 5.10-stable tree

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This is a note to let you know that I've just added the patch titled

    PCI: hv: Fix a race condition bug in hv_pci_query_relations()

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     pci-hv-fix-a-race-condition-bug-in-hv_pci_query_relations.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 440b5e3663271b0ffbd4908115044a6a51fb938b Mon Sep 17 00:00:00 2001
From: Dexuan Cui <decui@xxxxxxxxxxxxx>
Date: Wed, 14 Jun 2023 21:44:47 -0700
Subject: PCI: hv: Fix a race condition bug in hv_pci_query_relations()

From: Dexuan Cui <decui@xxxxxxxxxxxxx>

commit 440b5e3663271b0ffbd4908115044a6a51fb938b upstream.

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device-remove and the stack variable 'comp' is no longer valid;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().

Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs")
Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
Acked-by: Lorenzo Pieralisi <lpieralisi@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20230615044451.5580-2-decui@xxxxxxxxxxxxx
Signed-off-by: Wei Liu <wei.liu@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/pci/controller/pci-hyperv.c |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -2912,6 +2912,24 @@ static int hv_pci_query_relations(struct
 	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;
 }
 


Patches currently in stable-queue which might be from decui@xxxxxxxxxxxxx are

queue-5.10/pci-hv-fix-a-race-condition-in-hv_irq_unmask-that-can-cause-panic.patch
queue-5.10/revert-pci-hv-fix-a-timing-issue-which-causes-kdump-to-fail-occasionally.patch
queue-5.10/pci-hv-remove-the-useless-hv_pcichild_state-from-struct-hv_pci_dev.patch
queue-5.10/pci-hv-fix-a-race-condition-bug-in-hv_pci_query_relations.patch



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