fsdax: invalidate pages when CoW

CoW changes the share state of a dax page, but the share count of the page
isn't updated.  The next time access this page, it should have been a
newly accessed, but old association exists.  So, we need to clear the
share state when CoW happens, in both dax_iomap_rw() and dax_zero_iter().

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Shiyang Ruan <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Dave Chinner <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: John Hubbard <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: irides

fs/dax.c

@@ -1264,6 +1264,15 @@ static s64 dax_zero_iter(struct iomap_iter *iter, bool *did_zero)
 	if (srcmap->type == IOMAP_HOLE || srcmap->type == IOMAP_UNWRITTEN)
 		return length;
 
+	/*
+	 * invalidate the pages whose sharing state is to be changed
+	 * because of CoW.
+	 */
+	if (iomap->flags & IOMAP_F_SHARED)
+		invalidate_inode_pages2_range(iter->inode->i_mapping,
+					      pos >> PAGE_SHIFT,
+					      (pos + length - 1) >> PAGE_SHIFT);
+
 	do {
 		unsigned offset = offset_in_page(pos);
 		unsigned size = min_t(u64, PAGE_SIZE - offset, length);
@@ -1324,12 +1333,13 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
 		struct iov_iter *iter)
 {
 	const struct iomap *iomap = &iomi->iomap;
-	const struct iomap *srcmap = &iomi->srcmap;
+	const struct iomap *srcmap = iomap_iter_srcmap(iomi);
 	loff_t length = iomap_length(iomi);
 	loff_t pos = iomi->pos;
 	struct dax_device *dax_dev = iomap->dax_dev;
 	loff_t end = pos + length, done = 0;
 	bool write = iov_iter_rw(iter) == WRITE;
+	bool cow = write && iomap->flags & IOMAP_F_SHARED;
 	ssize_t ret = 0;
 	size_t xfer;
 	int id;
@@ -1356,7 +1366,7 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
 	 * into page tables. We have to tear down these mappings so that data
 	 * written by write(2) is visible in mmap.
 	 */
-	if (iomap->flags & IOMAP_F_NEW) {
+	if (iomap->flags & IOMAP_F_NEW || cow) {
 		invalidate_inode_pages2_range(iomi->inode->i_mapping,
 					      pos >> PAGE_SHIFT,
 					      (end - 1) >> PAGE_SHIFT);
@@ -1390,8 +1400,7 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
 			break;
 		}
 
-		if (write &&
-		    srcmap->type != IOMAP_HOLE && srcmap->addr != iomap->addr) {
+		if (cow) {
 			ret = dax_iomap_cow_copy(pos, length, PAGE_SIZE, srcmap,
 						 kaddr);
 			if (ret)