[PATCH RFC 07/15] powerpc/eeh: Sync eeh_add_to_parent_pe() and eeh_rmv_from_parent_pe()

[Sam Bobroff <sbobroff@linux.ibm.com>]

Note that even though there is currently only one place where a PE can
be removed from the parent/child tree (eeh_rmv_from_parent_pe()), it
is still protected against concurrent removal in case that changes in
the future.

Signed-off-by: Sam Bobroff <sbobroff@linux.ibm.com>
---
 arch/powerpc/kernel/eeh_pe.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/eeh_pe.c b/arch/powerpc/kernel/eeh_pe.c
index e89a30de2e7e..c9780b7109ec 100644
--- a/arch/powerpc/kernel/eeh_pe.c
+++ b/arch/powerpc/kernel/eeh_pe.c
@@ -528,6 +528,7 @@ int eeh_add_to_parent_pe(struct eeh_dev *edev)
 	struct eeh_pe *pe, *parent;
 	struct pci_dn *pdn = eeh_dev_to_pdn(edev);
 	int config_addr = (pdn->busno << 8) | (pdn->devfn);
+	unsigned long flags;
 
 	/* Check if the PE number is valid */
 	if (!eeh_has_flag(EEH_VALID_PE_ZERO) && !edev->pe_config_addr) {
@@ -541,6 +542,7 @@ int eeh_add_to_parent_pe(struct eeh_dev *edev)
 	 * PE should be composed of PCI bus and its subordinate
 	 * components.
 	 */
+	/* Acquire ref */
 	pe = eeh_pe_find(pdn->phb, edev->pe_config_addr, config_addr);
 	if (pe) {
 		if (pe->type & EEH_PE_INVALID) {
@@ -557,7 +559,6 @@ int eeh_add_to_parent_pe(struct eeh_dev *edev)
 				parent->type &= ~EEH_PE_INVALID;
 				parent = parent->parent;
 			}
-
 			eeh_edev_dbg(edev,
 				     "Added to device PE (parent: PE#%x)\n",
 				     pe->parent->addr);
@@ -570,10 +571,12 @@ int eeh_add_to_parent_pe(struct eeh_dev *edev)
 			list_add_tail(&edev->entry, &pe->edevs);
 			eeh_edev_dbg(edev, "Added to bus PE\n");
 		}
+		eeh_put_pe(pe); /* Release ref */
 		return 0;
 	}
 
 	/* Create a new EEH PE */
+	/* Acquire existence ref */
 	if (edev->physfn)
 		pe = eeh_pe_alloc(pdn->phb, EEH_PE_VF);
 	else
@@ -591,9 +594,9 @@ int eeh_add_to_parent_pe(struct eeh_dev *edev)
 	 * to PHB directly. Otherwise, we have to associate the
 	 * PE with its parent.
 	 */
-	parent = eeh_pe_get_parent(edev);
+	parent = eeh_pe_get_parent(edev); /* Acquire ref */
 	if (!parent) {
-		parent = eeh_phb_pe_get(pdn->phb);
+		parent = eeh_phb_pe_get(pdn->phb); /* Acquire ref */
 		if (!parent) {
 			pr_err("%s: No PHB PE is found (PHB Domain=%d)\n",
 				__func__, pdn->phb->global_number);
@@ -602,6 +605,7 @@ int eeh_add_to_parent_pe(struct eeh_dev *edev)
 			return -EEXIST;
 		}
 	}
+	eeh_lock_pes(&flags);
 	pe->parent = parent;
 
 	/*
@@ -609,10 +613,13 @@ int eeh_add_to_parent_pe(struct eeh_dev *edev)
 	 * link the EEH device accordingly.
 	 */
 	list_add_tail(&pe->child, &parent->child_list);
+	eeh_unlock_pes(flags);
 	list_add_tail(&edev->entry, &pe->edevs);
 	edev->pe = pe;
 	eeh_edev_dbg(edev, "Added to device PE (parent: PE#%x)\n",
-		     pe->parent->addr);
+		     parent->addr);
+	eeh_put_pe(parent); /* Release ref */
+	/* Retain existence ref */
 
 	return 0;
 }
@@ -631,12 +638,15 @@ int eeh_rmv_from_parent_pe(struct eeh_dev *edev)
 	struct eeh_pe *pe, *parent, *child;
 	bool keep, recover;
 	int cnt;
+	unsigned long flags;
 
+	/* TODO: Unsafe until eeh_dev can be synchronized * with eeh_pe. */
 	pe = eeh_dev_to_pe(edev);
 	if (!pe) {
 		eeh_edev_dbg(edev, "No PE found for device.\n");
 		return -EEXIST;
 	}
+	eeh_get_pe(pe); /* Acquire ref */
 
 	/* Remove the EEH device */
 	edev->pe = NULL;
@@ -648,6 +658,7 @@ int eeh_rmv_from_parent_pe(struct eeh_dev *edev)
 	 * delete the parent PE if it doesn't have associated
 	 * child PEs and EEH devices.
 	 */
+	eeh_lock_pes(&flags);
 	while (1) {
 		parent = pe->parent;
 
@@ -699,8 +710,15 @@ int eeh_rmv_from_parent_pe(struct eeh_dev *edev)
 			}
 		}
 
+		if (!parent)
+			break; /* PE has been removed */
+
+		eeh_get_pe(parent); /* Acquire ref */
+		eeh_put_pe(pe); /* Release ref */
 		pe = parent;
 	}
+	eeh_unlock_pes(flags);
+	eeh_put_pe(pe); /* Release ref */
 
 	return 0;
 }
-- 
2.22.0.216.g00a2a96fc9