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Commit 4f7d4614 authored by Vladimir Davydov's avatar Vladimir Davydov Committed by Linus Torvalds
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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: default avatarVladimir 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus 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;