only allow nonlinear vmas for ram backed filesystems

page_mkclean() doesn't re-protect ptes for non-linear mappings, so a later re-dirty through such a mapping will not generate a fault, PG_dirty will not reflect the dirty state and the dirty count will be skewed. This implies that msync() is also currently broken for nonlinear mappings. The easiest solution is to emulate remap_file_pages on non-linear mappings with simple mmap() for non ram-backed filesystems. Applications continue to work (albeit slower), as long as the number of remappings remain below the maximum vma count. However all currently known real uses of non-linear mappings are for ram backed filesystems, which this patch doesn't affect. Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: William Lee Irwin III <wli@holomorphy.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

only allow nonlinear vmas for ram backed filesystems
page_mkclean() doesn't re-protect ptes for non-linear mappings, so a later re-dirty through such a mapping will not generate a fault, PG_dirty will not reflect the dirty state and the dirty count will be skewed. This implies that msync() is also currently broken for nonlinear mappings. The easiest solution is to emulate remap_file_pages on non-linear mappings with simple mmap() for non ram-backed filesystems. Applications continue to work (albeit slower), as long as the number of remappings remain below the maximum vma count. However all currently known real uses of non-linear mappings are for ram backed filesystems, which this patch doesn't affect. Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: William Lee Irwin III <wli@holomorphy.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Miklos Szeredi · Linus Torvalds
1 parent bb2d5ce164
Showing 1 changed file with 19 additions and 0 deletions Side-by-side Diff
mm/fremap.c
@@ -181,6 +181,25 @@
 			goto retry;
 		}
 		mapping = vma->vm_file->f_mapping;
+		/*
+		 * page_mkclean doesn't work on nonlinear vmas, so if
+		 * dirty pages need to be accounted, emulate with linear
+		 * vmas.
+		 */
+		if (mapping_cap_account_dirty(mapping)) {
+			unsigned long addr;
+
+			flags &= MAP_NONBLOCK;
+			addr = mmap_region(vma->vm_file, start, size,
+					flags, vma->vm_flags, pgoff, 1);
+			if (IS_ERR_VALUE(addr)) {
+				err = addr;
+			} else {
+				BUG_ON(addr != start);
+				err = 0;
+			}
+			goto out;
+		}
 		spin_lock(&mapping->i_mmap_lock);
 		flush_dcache_mmap_lock(mapping);
 		vma->vm_flags |= VM_NONLINEAR;
...	...	@@ -181,6 +181,25 @@
181	181	goto retry;
182	182	}
183	183	mapping = vma->vm_file->f_mapping;
	184	+ /*
	185	+ * page_mkclean doesn't work on nonlinear vmas, so if
	186	+ * dirty pages need to be accounted, emulate with linear
	187	+ * vmas.
	188	+ */
	189	+ if (mapping_cap_account_dirty(mapping)) {
	190	+ unsigned long addr;
	191	+
	192	+ flags &= MAP_NONBLOCK;
	193	+ addr = mmap_region(vma->vm_file, start, size,
	194	+ flags, vma->vm_flags, pgoff, 1);
	195	+ if (IS_ERR_VALUE(addr)) {
	196	+ err = addr;
	197	+ } else {
	198	+ BUG_ON(addr != start);
	199	+ err = 0;
	200	+ }
	201	+ goto out;
	202	+ }
184	203	spin_lock(&mapping->i_mmap_lock);
185	204	flush_dcache_mmap_lock(mapping);
186	205	vma->vm_flags \|= VM_NONLINEAR;