btrfs: Use filemap_range_has_page()

The current implementation of btrfs_page_exists_in_range() gives the
wrong answer if the workingset code has stored a shadow entry in the
page cache.  The filemap_range_has_page() function does not have this
problem, and it's shared code, so use it instead.
eigned-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/btrfs_inode.h

@@ -364,6 +364,10 @@ static inline void btrfs_print_data_csum_error(struct btrfs_inode *inode,
 			logical_start, csum, csum_expected, mirror_num);
 }
 
-bool btrfs_page_exists_in_range(struct inode *inode, loff_t start, loff_t end);
+static inline bool btrfs_page_exists_in_range(struct inode *inode,
+						loff_t start, loff_t end)
+{
+	return filemap_range_has_page(inode->i_mapping, start, end);
+}
 
 #endif

fs/btrfs/inode.c

@@ -7464,76 +7464,6 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len,
 	return ret;
 }
 
-bool btrfs_page_exists_in_range(struct inode *inode, loff_t start, loff_t end)
-{
-	struct radix_tree_root *root = &inode->i_mapping->page_tree;
-	bool found = false;
-	void **pagep = NULL;
-	struct page *page = NULL;
-	unsigned long start_idx;
-	unsigned long end_idx;
-
-	start_idx = start >> PAGE_SHIFT;
-
-	/*
-	 * end is the last byte in the last page.  end == start is legal
-	 */
-	end_idx = end >> PAGE_SHIFT;
-
-	rcu_read_lock();
-
-	/* Most of the code in this while loop is lifted from
-	 * find_get_page.  It's been modified to begin searching from a
-	 * page and return just the first page found in that range.  If the
-	 * found idx is less than or equal to the end idx then we know that
-	 * a page exists.  If no pages are found or if those pages are
-	 * outside of the range then we're fine (yay!) */
-	while (page == NULL &&
-	       radix_tree_gang_lookup_slot(root, &pagep, NULL, start_idx, 1)) {
-		page = radix_tree_deref_slot(pagep);
-		if (unlikely(!page))
-			break;
-
-		if (radix_tree_exception(page)) {
-			if (radix_tree_deref_retry(page)) {
-				page = NULL;
-				continue;
-			}
-			/*
-			 * Otherwise, shmem/tmpfs must be storing a swap entry
-			 * here as an exceptional entry: so return it without
-			 * attempting to raise page count.
-			 */
-			page = NULL;
-			break; /* TODO: Is this relevant for this use case? */
-		}
-
-		if (!page_cache_get_speculative(page)) {
-			page = NULL;
-			continue;
-		}
-
-		/*
-		 * Has the page moved?
-		 * This is part of the lockless pagecache protocol. See
-		 * include/linux/pagemap.h for details.
-		 */
-		if (unlikely(page != *pagep)) {
-			put_page(page);
-			page = NULL;
-		}
-	}
-
-	if (page) {
-		if (page->index <= end_idx)
-			found = true;
-		put_page(page);
-	}
-
-	rcu_read_unlock();
-	return found;
-}
-
 static int lock_extent_direct(struct inode *inode, u64 lockstart, u64 lockend,
 			      struct extent_state **cached_state, int writing)
 {