[09/12] dax: Allow DAX code to replace exceptional entries

Commit Message

Jan Kara March 10, 2016, 7:18 p.m. UTC

Currently we forbid page_cache_tree_insert() to replace exceptional radix
tree entries for DAX inodes. However to make DAX faults race free we will
lock radix tree entries and when hole is created, we need to replace
such locked radix tree entry with a hole page. So modify
page_cache_tree_insert() to allow that.

Signed-off-by: Jan Kara <[e-mail]>
---
 include/linux/dax.h |  6 ++++++
 mm/filemap.c        | 18 +++++++++++-------
 2 files changed, 17 insertions(+), 7 deletions(-)

Patch

diff --git a/include/linux/dax.h b/include/linux/dax.h
index 7c45ac7ea1d1..4b63923e1f8d 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -3,8 +3,14 @@ 
 
 #include <linux/fs.h>
 #include <linux/mm.h>
+#include <linux/radix-tree.h>
 #include <asm/pgtable.h>
 
+/*
+ * Since exceptional entries do not use indirect bit, we reuse it as a lock bit
+ */
+#define DAX_ENTRY_LOCK RADIX_TREE_INDIRECT_PTR
+
 ssize_t dax_do_io(struct kiocb *, struct inode *, struct iov_iter *, loff_t,
 		  get_block_t, dio_iodone_t, int flags);
 int dax_clear_sectors(struct block_device *bdev, sector_t _sector, long _size);
diff --git a/mm/filemap.c b/mm/filemap.c
index 3461d97ecb30..262e6eff0b66 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -583,14 +583,18 @@  static int page_cache_tree_insert(struct address_space *mapping,
 		if (!radix_tree_exceptional_entry(p))
 			return -EEXIST;
 
-		if (WARN_ON(dax_mapping(mapping)))
-			return -EINVAL;
-
-		if (shadowp)
-			*shadowp = p;
 		mapping->nrexceptional--;
-		if (node)
-			workingset_node_shadows_dec(node);
+		if (!dax_mapping(mapping)) {
+			if (shadowp)
+				*shadowp = p;
+			if (node)
+				workingset_node_shadows_dec(node);
+		} else {
+			/* DAX can replace empty locked entry with a hole */
+			WARN_ON_ONCE(p !=
+				(void *)(RADIX_TREE_EXCEPTIONAL_ENTRY |
+					 DAX_ENTRY_LOCK));
+		}
 	}
 	radix_tree_replace_slot(slot, page);
 	mapping->nrpages++;