[PATCH] dax: Fix inconsistency between mmap and write(2)

[Jan Kara]

When a process has a PMD-sized hole mapped via mmap and later allocates
part of the file underlying this area using write(2), memory mappings
need not be appropriately invalidated if the file has no hole pages
allocated and thus view via mmap will not show the data written by
write(2). Fix the problem by always invalidating memory mappings
covering part of the file for which blocks got allocated.

Signed-off-by: Jan Kara <jack@xxxxxxx>
---
 fs/dax.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 85abd741253d..da7bc44e5725 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1028,11 +1028,11 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 		return -EIO;
 
 	/*
-	 * Write can allocate block for an area which has a hole page mapped
-	 * into page tables. We have to tear down these mappings so that data
-	 * written by write(2) is visible in mmap.
+	 * Write can allocate block for an area which has a hole page or zero
+	 * PMD entry in the radix tree.  We have to tear down these mappings so
+	 * that data written by write(2) is visible in mmap.
 	 */
-	if ((iomap->flags & IOMAP_F_NEW) && inode->i_mapping->nrpages) {
+	if (iomap->flags & IOMAP_F_NEW) {
 		invalidate_inode_pages2_range(inode->i_mapping,
 					      pos >> PAGE_SHIFT,
 					      (end - 1) >> PAGE_SHIFT);
-- 
2.12.0


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