[RESEND PATCH v3] cxl: Wrap iterations over afu slices inside 'afu_list_lock'

[Vaibhav Jain <vaibhav@linux.ibm.com>]

Within cxl module, iteration over array 'adapter->afu' may be racy
at few points as it might be simultaneously read during an EEH and its
contents being set to NULL while driver is being unloaded or unbound
from the adapter. This might result in a NULL pointer to 'struct afu'
being de-referenced during an EEH thereby causing a kernel oops.

This patch fixes this by making sure that all access to the array
'adapter->afu' is wrapped within the context of spin-lock
'adapter->afu_list_lock'.

Cc: stable@vger.kernel.org
Fixes: 9e8df8a2196("cxl: EEH support")
Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Acked-by: Frederic Barrat <fbarrat@linux.ibm.com>
Acked-by: Christophe Lombard <clombard@linux.vnet.ibm.com>
Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
---
Changelog:

Resend:
* Fixed the reference to 'adapter->afu' in patch description. [Andrew]
* Added the 'Fixes' tag and marked the patch to stable

v3:
* Updated a slice loop in cxl_pci_error_detectected() to ignore NULL
  slices [Fred]
* Added a NULL AFU check in cxl_pci_slot_reset() [Fred]

v2:
* Fixed a wrong comparison of non-null pointer [Fred]
* Moved a call to cxl_vphb_error_detected() within a branch that
  checks for not null AFU pointer in 'adapter->slices' [Fred]
* Removed a misleading comment in code.
---
 drivers/misc/cxl/guest.c |  2 ++
 drivers/misc/cxl/pci.c   | 39 ++++++++++++++++++++++++++++++---------
 2 files changed, 32 insertions(+), 9 deletions(-)

diff --git a/drivers/misc/cxl/guest.c b/drivers/misc/cxl/guest.c
index 5d28d9e454f5..08f4a512afad 100644
--- a/drivers/misc/cxl/guest.c
+++ b/drivers/misc/cxl/guest.c
@@ -267,6 +267,7 @@ static int guest_reset(struct cxl *adapter)
 	int i, rc;
 
 	pr_devel("Adapter reset request\n");
+	spin_lock(&adapter->afu_list_lock);
 	for (i = 0; i < adapter->slices; i++) {
 		if ((afu = adapter->afu[i])) {
 			pci_error_handlers(afu, CXL_ERROR_DETECTED_EVENT,
@@ -283,6 +284,7 @@ static int guest_reset(struct cxl *adapter)
 			pci_error_handlers(afu, CXL_RESUME_EVENT, 0);
 		}
 	}
+	spin_unlock(&adapter->afu_list_lock);
 	return rc;
 }
 
diff --git a/drivers/misc/cxl/pci.c b/drivers/misc/cxl/pci.c
index c79ba1c699ad..300531d6136f 100644
--- a/drivers/misc/cxl/pci.c
+++ b/drivers/misc/cxl/pci.c
@@ -1805,7 +1805,7 @@ static pci_ers_result_t cxl_vphb_error_detected(struct cxl_afu *afu,
 	/* There should only be one entry, but go through the list
 	 * anyway
 	 */
-	if (afu->phb == NULL)
+	if (afu == NULL || afu->phb == NULL)
 		return result;
 
 	list_for_each_entry(afu_dev, &afu->phb->bus->devices, bus_list) {
@@ -1832,7 +1832,8 @@ static pci_ers_result_t cxl_pci_error_detected(struct pci_dev *pdev,
 {
 	struct cxl *adapter = pci_get_drvdata(pdev);
 	struct cxl_afu *afu;
-	pci_ers_result_t result = PCI_ERS_RESULT_NEED_RESET, afu_result;
+	pci_ers_result_t result = PCI_ERS_RESULT_NEED_RESET;
+	pci_ers_result_t afu_result = PCI_ERS_RESULT_NEED_RESET;
 	int i;
 
 	/* At this point, we could still have an interrupt pending.
@@ -1843,6 +1844,7 @@ static pci_ers_result_t cxl_pci_error_detected(struct pci_dev *pdev,
 
 	/* If we're permanently dead, give up. */
 	if (state == pci_channel_io_perm_failure) {
+		spin_lock(&adapter->afu_list_lock);
 		for (i = 0; i < adapter->slices; i++) {
 			afu = adapter->afu[i];
 			/*
@@ -1851,6 +1853,7 @@ static pci_ers_result_t cxl_pci_error_detected(struct pci_dev *pdev,
 			 */
 			cxl_vphb_error_detected(afu, state);
 		}
+		spin_unlock(&adapter->afu_list_lock);
 		return PCI_ERS_RESULT_DISCONNECT;
 	}
 
@@ -1932,11 +1935,17 @@ static pci_ers_result_t cxl_pci_error_detected(struct pci_dev *pdev,
 	 *     * In slot_reset, free the old resources and allocate new ones.
 	 *     * In resume, clear the flag to allow things to start.
 	 */
+
+	/* Make sure no one else changes the afu list */
+	spin_lock(&adapter->afu_list_lock);
+
 	for (i = 0; i < adapter->slices; i++) {
 		afu = adapter->afu[i];
 
-		afu_result = cxl_vphb_error_detected(afu, state);
+		if (afu == NULL)
+			continue;
 
+		afu_result = cxl_vphb_error_detected(afu, state);
 		cxl_context_detach_all(afu);
 		cxl_ops->afu_deactivate_mode(afu, afu->current_mode);
 		pci_deconfigure_afu(afu);
@@ -1948,6 +1957,7 @@ static pci_ers_result_t cxl_pci_error_detected(struct pci_dev *pdev,
 			 (result == PCI_ERS_RESULT_NEED_RESET))
 			result = PCI_ERS_RESULT_NONE;
 	}
+	spin_unlock(&adapter->afu_list_lock);
 
 	/* should take the context lock here */
 	if (cxl_adapter_context_lock(adapter) != 0)
@@ -1980,14 +1990,18 @@ static pci_ers_result_t cxl_pci_slot_reset(struct pci_dev *pdev)
 	 */
 	cxl_adapter_context_unlock(adapter);
 
+	spin_lock(&adapter->afu_list_lock);
 	for (i = 0; i < adapter->slices; i++) {
 		afu = adapter->afu[i];
 
+		if (afu == NULL)
+			continue;
+
 		if (pci_configure_afu(afu, adapter, pdev))
-			goto err;
+			goto err_unlock;
 
 		if (cxl_afu_select_best_mode(afu))
-			goto err;
+			goto err_unlock;
 
 		if (afu->phb == NULL)
 			continue;
@@ -1999,16 +2013,16 @@ static pci_ers_result_t cxl_pci_slot_reset(struct pci_dev *pdev)
 			ctx = cxl_get_context(afu_dev);
 
 			if (ctx && cxl_release_context(ctx))
-				goto err;
+				goto err_unlock;
 
 			ctx = cxl_dev_context_init(afu_dev);
 			if (IS_ERR(ctx))
-				goto err;
+				goto err_unlock;
 
 			afu_dev->dev.archdata.cxl_ctx = ctx;
 
 			if (cxl_ops->afu_check_and_enable(afu))
-				goto err;
+				goto err_unlock;
 
 			afu_dev->error_state = pci_channel_io_normal;
 
@@ -2029,8 +2043,13 @@ static pci_ers_result_t cxl_pci_slot_reset(struct pci_dev *pdev)
 				result = PCI_ERS_RESULT_DISCONNECT;
 		}
 	}
+
+	spin_unlock(&adapter->afu_list_lock);
 	return result;
 
+err_unlock:
+	spin_unlock(&adapter->afu_list_lock);
+
 err:
 	/* All the bits that happen in both error_detected and cxl_remove
 	 * should be idempotent, so we don't need to worry about leaving a mix
@@ -2051,10 +2070,11 @@ static void cxl_pci_resume(struct pci_dev *pdev)
 	 * This is not the place to be checking if everything came back up
 	 * properly, because there's no return value: do that in slot_reset.
 	 */
+	spin_lock(&adapter->afu_list_lock);
 	for (i = 0; i < adapter->slices; i++) {
 		afu = adapter->afu[i];
 
-		if (afu->phb == NULL)
+		if (afu == NULL || afu->phb == NULL)
 			continue;
 
 		list_for_each_entry(afu_dev, &afu->phb->bus->devices, bus_list) {
@@ -2063,6 +2083,7 @@ static void cxl_pci_resume(struct pci_dev *pdev)
 				afu_dev->driver->err_handler->resume(afu_dev);
 		}
 	}
+	spin_unlock(&adapter->afu_list_lock);
 }
 
 static const struct pci_error_handlers cxl_err_handler = {
-- 
2.20.1