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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: Andrea Arcangeli <aarcange@redhat.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrea Arcangeli 2016-02-05 15:36:13 -08:00 committed by Linus Torvalds
parent af1ddcb5c6
commit acf128d048
1 changed files with 5 additions and 2 deletions
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7
mm/mmap.c
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@ -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);