dax: ensure that zero pages are removed from other processes
If the first access to a huge page was a store, there would be no existing
zero pmd in this process's page tables. There could be a zero pmd in
another process's page tables, if it had done a load. We can detect this
case by noticing that the buffer_head returned from the filesystem is New,
and ensure that other processes mapping this huge page have their page
tables flushed.
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Reported-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
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 d778e5f..74838c4 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -568,7 +568,11 @@
if ((pgoff | PG_PMD_COLOUR) >= size)
goto fallback;
- if (is_huge_zero_pmd(*pmd))
+ /*
+ * If we allocated new storage, make sure no process has any
+ * zero pages covering this hole
+ */
+ if (buffer_new(&bh))
unmap_mapping_range(mapping, pgoff << PAGE_SHIFT, PMD_SIZE, 0);
if (!write && !buffer_mapped(&bh) && buffer_uptodate(&bh)) {