[PATCH 1/2] PCIe hotplug interrupt and AER deadlock with reset_lock and device_lock

[Ian May <ian.may@canonical.com>]

Currently when a hotplug interrupt and AER recovery triggers simultaneously
the following deadlock can occur.

        Hotplug				       AER
----------------------------       ---------------------------
device_lock(&dev->dev)		   down_write(&ctrl->reset_lock)
down_read(&ctrl->reset_lock)       device_lock(&dev->dev)

This patch adds a reset_lock and reset_unlock hotplug_slot_op.  This would allow
the controller reset_lock/reset_unlock to be moved from pciehp_reset_slot to
pci_slot_reset function allowing the controller reset_lock to be acquired before
the device lock allowing for both hotplug and AER to grab the reset_lock
and device lock in proper order.

Signed-off-by: Ian May <ian.may@canonical.com>
---
 drivers/pci/hotplug/pciehp.h      |  2 ++
 drivers/pci/hotplug/pciehp_core.c |  2 ++
 drivers/pci/hotplug/pciehp_hpc.c  | 21 ++++++++++++++++++---
 drivers/pci/pci.c                 |  6 ++++++
 include/linux/pci_hotplug.h       |  2 ++
 5 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h
index e28b4fffd84d..1e98604cec83 100644
--- a/drivers/pci/hotplug/pciehp.h
+++ b/drivers/pci/hotplug/pciehp.h
@@ -183,6 +183,8 @@ void pciehp_release_ctrl(struct controller *ctrl);
 
 int pciehp_sysfs_enable_slot(struct hotplug_slot *hotplug_slot);
 int pciehp_sysfs_disable_slot(struct hotplug_slot *hotplug_slot);
+int pciehp_reset_lock(struct hotplug_slot *hotplug_slot);
+int pciehp_reset_unlock(struct hotplug_slot *hotplug_slot);
 int pciehp_reset_slot(struct hotplug_slot *hotplug_slot, int probe);
 int pciehp_get_attention_status(struct hotplug_slot *hotplug_slot, u8 *status);
 int pciehp_set_raw_indicator_status(struct hotplug_slot *h_slot, u8 status);
diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
index 4c032d75c874..a8da3e6a59b8 100644
--- a/drivers/pci/hotplug/pciehp_core.c
+++ b/drivers/pci/hotplug/pciehp_core.c
@@ -63,6 +63,8 @@ static int init_slot(struct controller *ctrl)
 	ops->get_power_status = get_power_status;
 	ops->get_adapter_status = get_adapter_status;
 	ops->reset_slot = pciehp_reset_slot;
+	ops->reset_lock = pciehp_reset_lock;
+	ops->reset_unlock = pciehp_reset_unlock;
 	if (MRL_SENS(ctrl))
 		ops->get_latch_status = get_latch_status;
 	if (ATTN_LED(ctrl)) {
diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
index 81b23f07719e..185ec9d1b0d0 100644
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/drivers/pci/hotplug/pciehp_hpc.c
@@ -798,6 +798,24 @@ void pcie_disable_interrupt(struct controller *ctrl)
 	pcie_write_cmd(ctrl, 0, mask);
 }
 
+int pciehp_reset_lock(struct hotplug_slot *hotplug_slot)
+{
+	struct controller *ctrl = to_ctrl(hotplug_slot);
+
+	down_write(&ctrl->reset_lock);
+
+	return 0;
+}
+
+int pciehp_reset_unlock(struct hotplug_slot *hotplug_slot)
+{
+	struct controller *ctrl = to_ctrl(hotplug_slot);
+
+	up_write(&ctrl->reset_lock);
+
+	return 0;
+}
+
 /*
  * pciehp has a 1:1 bus:slot relationship so we ultimately want a secondary
  * bus reset of the bridge, but at the same time we want to ensure that it is
@@ -816,8 +834,6 @@ int pciehp_reset_slot(struct hotplug_slot *hotplug_slot, int probe)
 	if (probe)
 		return 0;
 
-	down_write(&ctrl->reset_lock);
-
 	if (!ATTN_BUTTN(ctrl)) {
 		ctrl_mask |= PCI_EXP_SLTCTL_PDCE;
 		stat_mask |= PCI_EXP_SLTSTA_PDC;
@@ -836,7 +852,6 @@ int pciehp_reset_slot(struct hotplug_slot *hotplug_slot, int probe)
 	ctrl_dbg(ctrl, "%s: SLOTCTRL %x write cmd %x\n", __func__,
 		 pci_pcie_cap(ctrl->pcie->port) + PCI_EXP_SLTCTL, ctrl_mask);
 
-	up_write(&ctrl->reset_lock);
 	return rc;
 }
 
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index da21293f1111..e32c5a1a706e 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5228,14 +5228,20 @@ static int pci_slot_reset(struct pci_slot *slot, int probe)
 		return -ENOTTY;
 
 	if (!probe)
+	{
+		slot->hotplug->ops->reset_lock(slot->hotplug);
 		pci_slot_lock(slot);
+	}
 
 	might_sleep();
 
 	rc = pci_reset_hotplug_slot(slot->hotplug, probe);
 
 	if (!probe)
+	{
 		pci_slot_unlock(slot);
+		slot->hotplug->ops->reset_unlock(slot->hotplug);
+	}
 
 	return rc;
 }
diff --git a/include/linux/pci_hotplug.h b/include/linux/pci_hotplug.h
index f694eb2ca978..fce5ad979346 100644
--- a/include/linux/pci_hotplug.h
+++ b/include/linux/pci_hotplug.h
@@ -45,6 +45,8 @@ struct hotplug_slot_ops {
 	int (*get_latch_status)		(struct hotplug_slot *slot, u8 *value);
 	int (*get_adapter_status)	(struct hotplug_slot *slot, u8 *value);
 	int (*reset_slot)		(struct hotplug_slot *slot, int probe);
+	int (*reset_lock)               (struct hotplug_slot *slot);
+	int (*reset_unlock)             (struct hotplug_slot *slot);
 };
 
 /**
-- 
2.25.1