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fix some memory leaks detected by miri (#4959)
The first leak: ```rust #[test] fn blob_vec_drop_empty_capacity() { let item_layout = Layout:🆕:<Foo>(); let drop = drop_ptr::<Foo>; let _ = unsafe { BlobVec::new(item_layout, Some(drop), 0) }; } ``` this is because we allocate the swap scratch in blobvec regardless of what the capacity is, but we only deallocate if capacity is > 0 The second leak: ```rust #[test] fn panic_while_overwriting_component() { let helper = DropTestHelper::new(); let res = panic::catch_unwind(|| { let mut world = World::new(); world .spawn() .insert(helper.make_component(true, 0)) .insert(helper.make_component(false, 1)); println!("Done inserting! Dropping world..."); }); let drop_log = helper.finish(res); assert_eq!( &*drop_log, [ DropLogItem::Create(0), DropLogItem::Create(1), DropLogItem::Drop(0), ] ); } ``` this is caused by us not running the drop impl on the to-be-inserted component if the drop impl of the overwritten component panics --- managed to figure out where the leaks were by using this 10/10 command ``` cargo --quiet test --lib -- --list | sed 's/: test$//' | MIRIFLAGS="-Zmiri-disable-isolation" xargs -n1 cargo miri test --lib -- --exact ``` which runs every test one by one rather than all at once which let miri actually tell me which test had the leak 🙃
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3 changed files with 20 additions and 4 deletions
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.github/workflows/ci.yml
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.github/workflows/ci.yml
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@ -99,11 +99,10 @@ jobs:
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RUSTFLAGS: -Zrandomize-layout
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# https://github.com/rust-lang/miri#miri--z-flags-and-environment-variables
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# -Zmiri-disable-isolation is needed because our executor uses `fastrand` which accesses system time.
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# -Zmiri-ignore-leaks is needed because running bevy_ecs tests finds a memory leak but its impossible
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# to track down because allocids are nondeterministic.
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# -Zmiri-permissive-provenance disables warnings against int2ptr casts (since those are used by once_cell)
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# -Zmiri-disable-weak-memory-emulation works around https://github.com/bevyengine/bevy/issues/5164.
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MIRIFLAGS: -Zmiri-disable-isolation -Zmiri-ignore-leaks -Zmiri-permissive-provenance -Zmiri-disable-weak-memory-emulation
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# -Zmiri-ignore-leaks is necessary because a bunch of tests don't join all threads before finishing.
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MIRIFLAGS: -Zmiri-ignore-leaks -Zmiri-disable-isolation -Zmiri-permissive-provenance -Zmiri-disable-weak-memory-emulation
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check-compiles:
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runs-on: ubuntu-latest
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@ -151,8 +151,20 @@ impl BlobVec {
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let ptr = self.get_unchecked_mut(index).promote().as_ptr();
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self.len = 0;
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// Drop the old value, then write back, justifying the promotion
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// If the drop impl for the old value panics then we run the drop impl for `value` too.
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if let Some(drop) = self.drop {
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struct OnDrop<F: FnMut()>(F);
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impl<F: FnMut()> Drop for OnDrop<F> {
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fn drop(&mut self) {
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(self.0)();
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}
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}
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let value = value.as_ptr();
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let on_unwind = OnDrop(|| (drop)(OwningPtr::new(NonNull::new_unchecked(value))));
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(drop)(OwningPtr::new(NonNull::new_unchecked(ptr)));
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core::mem::forget(on_unwind);
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}
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std::ptr::copy_nonoverlapping::<u8>(value.as_ptr(), ptr, self.item_layout.size());
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self.len = old_len;
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@ -304,12 +316,16 @@ impl BlobVec {
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impl Drop for BlobVec {
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fn drop(&mut self) {
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self.clear();
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if self.item_layout.size() > 0 {
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unsafe {
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std::alloc::dealloc(self.swap_scratch.as_ptr(), self.item_layout);
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}
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}
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let array_layout =
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array_layout(&self.item_layout, self.capacity).expect("array layout should be valid");
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if array_layout.size() > 0 {
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unsafe {
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std::alloc::dealloc(self.get_ptr_mut().as_ptr(), array_layout);
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std::alloc::dealloc(self.swap_scratch.as_ptr(), self.item_layout);
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}
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}
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}
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@ -1693,6 +1693,7 @@ mod tests {
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DropLogItem::Create(0),
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DropLogItem::Create(1),
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DropLogItem::Drop(0),
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DropLogItem::Drop(1),
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]
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);
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}
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