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util/interval-tree: Use qatomic_read for left/right while searching

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Fixes a race condition (generally without optimization) in which
the subtree is re-read after the protecting if condition.

Cc: qemu-stable@nongnu.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2023-07-22 20:43:45 +01:00
parent 234320cd05
commit 055b86e0f0
1 changed files with 9 additions and 6 deletions
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15
util/interval-tree.c
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@ -745,8 +745,9 @@ static IntervalTreeNode *interval_tree_subtree_search(IntervalTreeNode *node,
* Loop invariant: start <= node->subtree_last
* (Cond2 is satisfied by one of the subtree nodes)
*/
if (node->rb.rb_left) {
IntervalTreeNode *left = rb_to_itree(node->rb.rb_left);
RBNode *tmp = qatomic_read(&node->rb.rb_left);
if (tmp) {
IntervalTreeNode *left = rb_to_itree(tmp);
if (start <= left->subtree_last) {
/*
@ -765,8 +766,9 @@ static IntervalTreeNode *interval_tree_subtree_search(IntervalTreeNode *node,
if (start <= node->last) { /* Cond2 */
return node; /* node is leftmost match */
}
if (node->rb.rb_right) {
node = rb_to_itree(node->rb.rb_right);
tmp = qatomic_read(&node->rb.rb_right);
if (tmp) {
node = rb_to_itree(tmp);
if (start <= node->subtree_last) {
continue;
}
@ -814,8 +816,9 @@ IntervalTreeNode *interval_tree_iter_first(IntervalTreeRoot *root,
IntervalTreeNode *interval_tree_iter_next(IntervalTreeNode *node,
uint64_t start, uint64_t last)
{
RBNode *rb = node->rb.rb_right, *prev;
RBNode *rb, *prev;
rb = qatomic_read(&node->rb.rb_right);
while (true) {
/*
* Loop invariants:
@ -840,7 +843,7 @@ IntervalTreeNode *interval_tree_iter_next(IntervalTreeNode *node,
}
prev = &node->rb;
node = rb_to_itree(rb);
rb = node->rb.rb_right;
rb = qatomic_read(&node->rb.rb_right);
} while (prev == rb);
/* Check if the node intersects [start;last] */