Commit 73a6ec47 authored Sep 08, 2015 by Matthew Wilcox Committed by Linus Torvalds Sep 08, 2015

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>

parent d295e341

fs/dax.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -568,7 +568,11 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
		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)) {