[PATCH 4.19 134/142] dax: Check page->mapping isnt NULL

Greg Kroah-Hartman
2018-12-14T12:36:26Z

From: Matthew Wilcox <willy@infradead.org>

commit c93db7bb6ef3251e0ea48ade311d3e9942748e1c upstream.

If we race with inode destroy, it's possible for page->mapping to be
NULL before we even enter this routine, as well as after having slept
waiting for the dax entry to become unlocked.

Fixes: c2a7d2a11552 ("filesystem-dax: Introduce dax_lock_mapping_entry()")
Cc: <stable@vger.kernel.org>
Reported-by: Jan Kara <jack@suse.cz>
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/dax.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/dax.c
+++ b/fs/dax.c
@@ -423,7 +423,7 @@ bool dax_lock_mapping_entry(struct page
for (;;) {
mapping = READ_ONCE(page->mapping);

- if (!dax_mapping(mapping))
+ if (!mapping || !dax_mapping(mapping))
break;

/*