Merge tag 'dax-for-5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm

Pull dax updates from Dan Williams:
 "The fruits of a bug hunt in the fsdax implementation with Willy and a
  small feature update for device-dax:

   - Fix a hang condition that started triggering after the Xarray
     conversion of fsdax in the v4.20 kernel.

   - Add a 'resource' (root-only physical base address) sysfs attribute
     to device-dax instances to correlate memory-blocks onlined via the
     kmem driver with a given device instance"

* tag 'dax-for-5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm:
  dax: Fix missed wakeup with PMD faults
  device-dax: Add a 'resource' attribute

Author: torvalds

drivers/dax/bus.c

@@ -295,6 +295,22 @@ static ssize_t target_node_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(target_node);
 
+static unsigned long long dev_dax_resource(struct dev_dax *dev_dax)
+{
+	struct dax_region *dax_region = dev_dax->region;
+
+	return dax_region->res.start;
+}
+
+static ssize_t resource_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct dev_dax *dev_dax = to_dev_dax(dev);
+
+	return sprintf(buf, "%#llx\n", dev_dax_resource(dev_dax));
+}
+static DEVICE_ATTR_RO(resource);
+
 static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
 		char *buf)
 {
@@ -313,13 +329,16 @@ static umode_t dev_dax_visible(struct kobject *kobj, struct attribute *a, int n)
 
 	if (a == &dev_attr_target_node.attr && dev_dax_target_node(dev_dax) < 0)
 		return 0;
+	if (a == &dev_attr_resource.attr)
+		return 0400;
 	return a->mode;
 }
 
 static struct attribute *dev_dax_attributes[] = {
 	&dev_attr_modalias.attr,
 	&dev_attr_size.attr,
 	&dev_attr_target_node.attr,
+	&dev_attr_resource.attr,
 	NULL,
 };
 

fs/dax.c

@@ -123,6 +123,15 @@ static int dax_is_empty_entry(void *entry)
 	return xa_to_value(entry) & DAX_EMPTY;
 }
 
+/*
+ * true if the entry that was found is of a smaller order than the entry
+ * we were looking for
+ */
+static bool dax_is_conflict(void *entry)
+{
+	return entry == XA_RETRY_ENTRY;
+}
+
 /*
  * DAX page cache entry locking
  */
@@ -195,11 +204,13 @@ static void dax_wake_entry(struct xa_state *xas, void *entry, bool wake_all)
  * Look up entry in page cache, wait for it to become unlocked if it
  * is a DAX entry and return it.  The caller must subsequently call
  * put_unlocked_entry() if it did not lock the entry or dax_unlock_entry()
- * if it did.
+ * if it did.  The entry returned may have a larger order than @order.
+ * If @order is larger than the order of the entry found in i_pages, this
+ * function returns a dax_is_conflict entry.
  *
  * Must be called with the i_pages lock held.
  */
-static void *get_unlocked_entry(struct xa_state *xas)
+static void *get_unlocked_entry(struct xa_state *xas, unsigned int order)
 {
 	void *entry;
 	struct wait_exceptional_entry_queue ewait;
@@ -210,6 +221,8 @@ static void *get_unlocked_entry(struct xa_state *xas)
 
 	for (;;) {
 		entry = xas_find_conflict(xas);
+		if (dax_entry_order(entry) < order)
+			return XA_RETRY_ENTRY;
 		if (!entry || WARN_ON_ONCE(!xa_is_value(entry)) ||
 				!dax_is_locked(entry))
 			return entry;
@@ -254,7 +267,7 @@ static void wait_entry_unlocked(struct xa_state *xas, void *entry)
 static void put_unlocked_entry(struct xa_state *xas, void *entry)
 {
 	/* If we were the only waiter woken, wake the next one */
-	if (entry)
+	if (entry && dax_is_conflict(entry))
 		dax_wake_entry(xas, entry, false);
 }
 
@@ -461,28 +474,25 @@ void dax_unlock_page(struct page *page, dax_entry_t cookie)
  * overlap with xarray value entries.
  */
 static void *grab_mapping_entry(struct xa_state *xas,
-		struct address_space *mapping, unsigned long size_flag)
+		struct address_space *mapping, unsigned int order)
 {
 	unsigned long index = xas->xa_index;
 	bool pmd_downgrade = false; /* splitting PMD entry into PTE entries? */
 	void *entry;
 
 retry:
 	xas_lock_irq(xas);
-	entry = get_unlocked_entry(xas);
+	entry = get_unlocked_entry(xas, order);
 
 	if (entry) {
+		if (dax_is_conflict(entry))
+			goto fallback;
 		if (!xa_is_value(entry)) {
 			xas_set_err(xas, EIO);
 			goto out_unlock;
 		}
 
-		if (size_flag & DAX_PMD) {
-			if (dax_is_pte_entry(entry)) {
-				put_unlocked_entry(xas, entry);
-				goto fallback;
-			}
-		} else { /* trying to grab a PTE entry */
+		if (order == 0) {
 			if (dax_is_pmd_entry(entry) &&
 			    (dax_is_zero_entry(entry) ||
 			     dax_is_empty_entry(entry))) {
@@ -523,7 +533,11 @@ static void *grab_mapping_entry(struct xa_state *xas,
 	if (entry) {
 		dax_lock_entry(xas, entry);
 	} else {
-		entry = dax_make_entry(pfn_to_pfn_t(0), size_flag | DAX_EMPTY);
+		unsigned long flags = DAX_EMPTY;
+
+		if (order > 0)
+			flags |= DAX_PMD;
+		entry = dax_make_entry(pfn_to_pfn_t(0), flags);
 		dax_lock_entry(xas, entry);
 		if (xas_error(xas))
 			goto out_unlock;
@@ -594,7 +608,7 @@ struct page *dax_layout_busy_page(struct address_space *mapping)
 		if (WARN_ON_ONCE(!xa_is_value(entry)))
 			continue;
 		if (unlikely(dax_is_locked(entry)))
-			entry = get_unlocked_entry(&xas);
+			entry = get_unlocked_entry(&xas, 0);
 		if (entry)
 			page = dax_busy_page(entry);
 		put_unlocked_entry(&xas, entry);
@@ -621,7 +635,7 @@ static int __dax_invalidate_entry(struct address_space *mapping,
 	void *entry;
 
 	xas_lock_irq(&xas);
-	entry = get_unlocked_entry(&xas);
+	entry = get_unlocked_entry(&xas, 0);
 	if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
 		goto out;
 	if (!trunc &&
@@ -848,7 +862,7 @@ static int dax_writeback_one(struct xa_state *xas, struct dax_device *dax_dev,
 	if (unlikely(dax_is_locked(entry))) {
 		void *old_entry = entry;
 
-		entry = get_unlocked_entry(xas);
+		entry = get_unlocked_entry(xas, 0);
 
 		/* Entry got punched out / reallocated? */
 		if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
@@ -1509,7 +1523,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
 	 * entry is already in the array, for instance), it will return
 	 * VM_FAULT_FALLBACK.
 	 */
-	entry = grab_mapping_entry(&xas, mapping, DAX_PMD);
+	entry = grab_mapping_entry(&xas, mapping, PMD_ORDER);
 	if (xa_is_internal(entry)) {
 		result = xa_to_internal(entry);
 		goto fallback;
@@ -1658,11 +1672,10 @@ dax_insert_pfn_mkwrite(struct vm_fault *vmf, pfn_t pfn, unsigned int order)
 	vm_fault_t ret;
 
 	xas_lock_irq(&xas);
-	entry = get_unlocked_entry(&xas);
+	entry = get_unlocked_entry(&xas, order);
 	/* Did we race with someone splitting entry or so? */
-	if (!entry ||
-	    (order == 0 && !dax_is_pte_entry(entry)) ||
-	    (order == PMD_ORDER && !dax_is_pmd_entry(entry))) {
+	if (!entry || dax_is_conflict(entry) ||
+	    (order == 0 && !dax_is_pte_entry(entry))) {
 		put_unlocked_entry(&xas, entry);
 		xas_unlock_irq(&xas);
 		trace_dax_insert_pfn_mkwrite_no_entry(mapping->host, vmf,