diff --git a/fs/dax.c b/fs/dax.c
index 2deed64b7eea728fb3a09f3e33238c8068c8935b..c694117a706208ccb325ee2e17bc33b62e7ba624 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -553,7 +553,12 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 	if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE)
 		goto fallback;
 
-	/* Guard against a race with truncate */
+	/*
+	 * If a truncate happened while we were allocating blocks, we may
+	 * leave blocks allocated to the file that are beyond EOF.  We can't
+	 * take i_mutex here, so just leave them hanging; they'll be freed
+	 * when the file is deleted.
+	 */
 	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (pgoff >= size) {
 		result = VM_FAULT_SIGBUS;