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 4.19-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-4.19 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device-remove and the stack variable 'comp' is no longer valid;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
@@ -2445,6 +2445,24 @@ 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-4.19/pci-hv-fix-a-race-condition-bug-in-hv_pci_query_relations.patch
