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gh-114944: Fix race between _PyParkingLot_Park and _PyParkingLot_UnparkAll when handling interrupts #114945

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Merged
merged 4 commits into from
Feb 5, 2024
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gh-114944: Fix race between _PyParkingLot_Park and _PyParkingLot_UnparkAll when handling interrupts #114945

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d68bf0d
Fix race between `_PyParkingLot_Park` and `_PyParkingLot_UnparkAll` w…
mpage Feb 3, 2024
cd85723
📜🤖 Added by blurb_it.
blurb-it[bot] Feb 3, 2024
33fea69
Set `is_unparking` in dequeue{_all}
mpage Feb 3, 2024
b06247d
Move node declaration back
mpage Feb 3, 2024
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core and Builtins/2024-02-03-01-48-38.gh-issue-114944.4J5ELD.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fixes a race between ``PyParkingLot_Park`` and ``_PyParkingLot_UnparkAll``.
6 changes: 5 additions & 1 deletion Python/parking_lot.c
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Expand Up @@ -356,14 +356,18 @@ _PyParkingLot_Unpark(const void *addr, _Py_unpark_fn_t *fn, void *arg)
void
_PyParkingLot_UnparkAll(const void *addr)
{
struct llist_node *node;
struct llist_node head = LLIST_INIT(head);
Bucket *bucket = &buckets[((uintptr_t)addr) % NUM_BUCKETS];

_PyRawMutex_Lock(&bucket->mutex);
dequeue_all(bucket, addr, &head);
llist_for_each(node, &head) {
struct wait_entry *waiter = llist_data(node, struct wait_entry, node);
waiter->is_unparking = true;
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This looks correct, but let's push the waiter->is_unparking assignment into dequeue_all and dequeue to avoid the extra loop here.

}
_PyRawMutex_Unlock(&bucket->mutex);

struct llist_node *node;
llist_for_each_safe(node, &head) {
struct wait_entry *waiter = llist_data(node, struct wait_entry, node);
llist_remove(node);
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