dax: improve comment about truncate race
Jan Kara pointed out I should be more explicit here about the perils of
racing against truncate. The comment is mostly the same as for the PTE
case.
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/dax.c b/fs/dax.c
index 2deed64..c694117 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -553,7 +553,12 @@
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;