[PATCH] dax: Change lock/unlock API

[Matthew Wilcox]

Return the unlock cookie from dax_lock_mapping_entry() and
pass it to dax_unlock_mapping_entry().  This fixes a bug where
dax_unlock_mapping_entry() was assuming that the page was PMD-aligned
if the entry was a PMD entry.

Debugged-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Fixes: 9f32d221301c ("dax: Convert dax_lock_mapping_entry to XArray")
Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
---
 fs/dax.c            | 21 ++++++++-------------
 include/linux/dax.h | 15 +++++++++------
 mm/memory-failure.c |  6 ++++--
 3 files changed, 21 insertions(+), 21 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 9bcce89ea18e..d2c04e802978 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -351,20 +351,20 @@ static struct page *dax_busy_page(void *entry)
  * @page: The page whose entry we want to lock
  *
  * Context: Process context.
- * Return: %true if the entry was locked or does not need to be locked.
+ * Return: A cookie to pass to dax_unlock_mapping_entry() or 0 if the
+ * entry could not be locked.
  */
-bool dax_lock_mapping_entry(struct page *page)
+dax_entry_t dax_lock_mapping_entry(struct page *page)
 {
 	XA_STATE(xas, NULL, 0);
 	void *entry;
-	bool locked;
 
 	/* Ensure page->mapping isn't freed while we look at it */
 	rcu_read_lock();
 	for (;;) {
 		struct address_space *mapping = READ_ONCE(page->mapping);
 
-		locked = false;
+		entry = NULL;
 		if (!dax_mapping(mapping))
 			break;
 
@@ -375,7 +375,7 @@ bool dax_lock_mapping_entry(struct page *page)
 		 * otherwise we would not have a valid pfn_to_page()
 		 * translation.
 		 */
-		locked = true;
+		entry = (void *)~0UL;
 		if (S_ISCHR(mapping->host->i_mode))
 			break;
 
@@ -400,23 +400,18 @@ bool dax_lock_mapping_entry(struct page *page)
 		break;
 	}
 	rcu_read_unlock();
-	return locked;
+	return (dax_entry_t)entry;
 }
 
-void dax_unlock_mapping_entry(struct page *page)
+void dax_unlock_mapping_entry(struct page *page, dax_entry_t entry)
 {
 	struct address_space *mapping = page->mapping;
 	XA_STATE(xas, &mapping->i_pages, page->index);
-	void *entry;
 
 	if (S_ISCHR(mapping->host->i_mode))
 		return;
 
-	rcu_read_lock();
-	entry = xas_load(&xas);
-	rcu_read_unlock();
-	entry = dax_make_entry(page_to_pfn_t(page), dax_is_pmd_entry(entry));
-	dax_unlock_entry(&xas, entry);
+	dax_unlock_entry(&xas, (void *)entry);
 }
 
 /*
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 450b28db9533..f3fcdf3cb86f 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -7,6 +7,8 @@
 #include <linux/radix-tree.h>
 #include <asm/pgtable.h>
 
+typedef unsigned long dax_entry_t;
+
 struct iomap_ops;
 struct dax_device;
 struct dax_operations {
@@ -88,8 +90,8 @@ int dax_writeback_mapping_range(struct address_space *mapping,
 		struct block_device *bdev, struct writeback_control *wbc);
 
 struct page *dax_layout_busy_page(struct address_space *mapping);
-bool dax_lock_mapping_entry(struct page *page);
-void dax_unlock_mapping_entry(struct page *page);
+dax_entry_t dax_lock_mapping_entry(struct page *page);
+void dax_unlock_mapping_entry(struct page *page, dax_entry_t cookie);
 #else
 static inline bool bdev_dax_supported(struct block_device *bdev,
 		int blocksize)
@@ -122,14 +124,15 @@ static inline int dax_writeback_mapping_range(struct address_space *mapping,
 	return -EOPNOTSUPP;
 }
 
-static inline bool dax_lock_mapping_entry(struct page *page)
+static inline dax_entry_t dax_lock_mapping_entry(struct page *page)
 {
 	if (IS_DAX(page->mapping->host))
-		return true;
-	return false;
+		return ~0UL;
+	return 0;
 }
 
-static inline void dax_unlock_mapping_entry(struct page *page)
+static inline
+void dax_unlock_mapping_entry(struct page *page, dax_entry_t cookie)
 {
 }
 #endif
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 0cd3de3550f0..688a406f31b3 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1161,6 +1161,7 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
 	LIST_HEAD(tokill);
 	int rc = -EBUSY;
 	loff_t start;
+	dax_entry_t cookie;
 
 	/*
 	 * Prevent the inode from being freed while we are interrogating
@@ -1169,7 +1170,8 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
 	 * also prevents changes to the mapping of this pfn until
 	 * poison signaling is complete.
 	 */
-	if (!dax_lock_mapping_entry(page))
+	cookie = dax_lock_mapping_entry(page);
+	if (!cookie)
 		goto out;
 
 	if (hwpoison_filter(page)) {
@@ -1220,7 +1222,7 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
 	kill_procs(&tokill, flags & MF_MUST_KILL, !unmap_success, pfn, flags);
 	rc = 0;
 unlock:
-	dax_unlock_mapping_entry(page);
+	dax_unlock_mapping_entry(page, cookie);
 out:
 	/* drop pgmap ref acquired in caller */
 	put_dev_pagemap(pgmap);
-- 
2.19.1