The patch titled
Subject: mm: validate_mm browse_rb SMP race condition
has been added to the -mm tree. Its filename is
mm-validate_mm-browse_rb-smp-race-condition.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-validate_mm-browse_rb-smp-race-condition.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-validate_mm-browse_rb-smp-race-condition.patch
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------------------------------------------------------
From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx>
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Tested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mmap.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff -puN mm/mmap.c~mm-validate_mm-browse_rb-smp-race-condition mm/mmap.c
--- a/mm/mmap.c~mm-validate_mm-browse_rb-smp-race-condition
+++ a/mm/mmap.c
@@ -390,8 +390,9 @@ static long vma_compute_subtree_gap(stru
}
#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 *roo
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->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);
_
Patches currently in -mm which might be from aarcange@xxxxxxxxxx are
mm-validate_mm-browse_rb-smp-race-condition.patch
ksm-introduce-ksm_max_page_sharing-per-page-deduplication-limit.patch
ksm-introduce-ksm_max_page_sharing-per-page-deduplication-limit-fix-3.patch
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