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Commit acf128d0 authored by Andrea Arcangeli's avatar Andrea Arcangeli Committed by Linus Torvalds
Browse files

mm: validate_mm browse_rb SMP race condition 



The mmap_sem for reading in validate_mm called from expand_stack is not
enough to prevent the argumented rbtree rb_subtree_gap information to
change from under us because expand_stack may be running from other
threads concurrently which will hold the mmap_sem for reading too.

The argumented rbtree is updated with vma_gap_update under the
page_table_lock so use it in browse_rb() too to avoid false positives.

Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
Tested-by: default avatarDmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent af1ddcb5

mm/mmap.c

+5 −2
Original line number Diff line number Diff line
@@ -390,8 +390,9 @@ static long vma_compute_subtree_gap(struct vm_area_struct *vma) 
}



#ifdef CONFIG_DEBUG_VM_RB

static int browse_rb(struct rb_root *root)

static int browse_rb(struct mm_struct *mm)

{

	struct rb_root *root = &mm->mm_rb;

	int i = 0, j, bug = 0;

	struct rb_node *nd, *pn = NULL;

	unsigned long prev = 0, pend = 0;
@@ -414,12 +415,14 @@ static int browse_rb(struct rb_root *root) 
				  vma->vm_start, vma->vm_end);

			bug = 1;

		}

		spin_lock(&mm->page_table_lock);

		if (vma->rb_subtree_gap != vma_compute_subtree_gap(vma)) {

			pr_emerg("free gap %lx, correct %lx\n",

			       vma->rb_subtree_gap,

			       vma_compute_subtree_gap(vma));

			bug = 1;

		}

		spin_unlock(&mm->page_table_lock);

		i++;

		pn = nd;

		prev = vma->vm_start;
@@ -475,7 +478,7 @@ static void validate_mm(struct mm_struct *mm) 
			  mm->highest_vm_end, highest_address);

		bug = 1;

	}

	i = browse_rb(&mm->mm_rb);

	i = browse_rb(mm);

	if (i != mm->map_count) {

		if (i != -1)

			pr_emerg("map_count %d rb %d\n", mm->map_count, i);