Commit 4f7d4614 authored Aug 08, 2014 by Vladimir Davydov Committed by Linus Torvalds Aug 08, 2014

fork: copy mm's vm usage counters under mmap_sem



If a forking process has a thread calling (un)mmap (silly but still),
the child process may have some of its mm's vm usage counters (total_vm
and friends) screwed up, because currently they are copied from oldmm
w/o holding any locks (memcpy in dup_mm).

This patch moves the counters initialization to dup_mmap() to be called
under oldmm->mmap_sem, which eliminates any possibility of race.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent ce65cefa

kernel/fork.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -374,6 +374,11 @@ static int dup_mmap(struct mm_struct mm, struct mm_struct oldmm)
		*/
		down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);

		mm->total_vm = oldmm->total_vm;
		mm->shared_vm = oldmm->shared_vm;
		mm->exec_vm = oldmm->exec_vm;
		mm->stack_vm = oldmm->stack_vm;

		rb_link = &mm->mm_rb.rb_node;
		rb_parent = NULL;
		pprev = &mm->mmap;

Admin message