Don't call assume_init on Deferred's Data #779
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In the crossbeam-deque test suite, a Deferred is created from a FnOnce which is smaller than the Data. This makes the call to assume_init() immediate UB (the reference to it created upon call is probably UB too). Since Data doesn't have a Drop impl, we can just leave it in the MaybeUninit wrapper.
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786: Prepare for the next release r=taiki-e a=taiki-e - crossbeam-epoch 0.9.6 -> 0.9.7 - Fix Miri error when `-Zmiri-check-number-validity` is enabled. (#779) - crossbeam-queue 0.3.3 -> 0.3.4 - Implement `IntoIterator` for `ArrayQueue` and `SegQueue`. (#772) - crossbeam-utils 0.8.6 -> 0.8.7 - Add `AtomicCell<i*,u*>::{fetch_max,fetch_min}`. (#785) - Add `AtomicCell<i*,u*,bool>::fetch_nand`. (#785) - Fix unsoundness of `AtomicCell<{i,u}64>` arithmetics on 32-bit targets that support `Atomic{I,U}64` (#781) Co-authored-by: Taiki Endo <te316e89@gmail.com>
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786: Prepare for the next release r=taiki-e a=taiki-e - crossbeam-epoch 0.9.6 -> 0.9.7 - Fix Miri error when `-Zmiri-check-number-validity` is enabled. (#779) - crossbeam-queue 0.3.3 -> 0.3.4 - Implement `IntoIterator` for `ArrayQueue` and `SegQueue`. (#772) - crossbeam-utils 0.8.6 -> 0.8.7 - Add `AtomicCell<{i*,u*}>::{fetch_max,fetch_min}`. (#785) - Add `AtomicCell<{i*,u*,bool}>::fetch_nand`. (#785) - Fix unsoundness of `AtomicCell<{i,u}64>` arithmetics on 32-bit targets that support `Atomic{I,U}64` (#781) Co-authored-by: Taiki Endo <te316e89@gmail.com>
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This situation can be observed by running
MIRIFLAGS="-Zmiri-check-number-validity" cargo miri testincrossbeam/crossbeam-deque:In the crossbeam-deque test suite, a
Deferredwas created from aFnOncewhich is smaller than theData. This makes the call toMaybeUninit::assume_init()immediate UB (the reference to it created upon call is probably UB too). The docs forMaybeUninit::assume_init()say this:Since
Datadoesn't have aDropimpl, we can just leave it in theMaybeUninitwrapper. This removes all issues about type validity.