Miri reports leaks

[emilio]

I think this might be a miri false positive. I was writing some tests for use_current_thread (#1052), and I thought they were my fault but they also repro in other tests.

$ cargo miri test --test scoped_threadpool
[...]
error: memory leaked: alloc137749 (Rust heap, size: 152, align: 8), allocated here:                                                                                                                                                         
   --> /home/emilio/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/alloc.rs:102:9                                                                                                               
    |                                                                                                                                                                                                                                       
102 |         __rust_alloc(layout.size(), layout.align())                                                                                                                                                                                   
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                                                                                                                                                                   
    |                                                                                                                                                                                                                                       
    = note: inside `std::alloc::alloc` at /home/emilio/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/alloc.rs:102:9: 102:52                                                                    
    = note: inside `std::alloc::Global::alloc_impl` at /home/emilio/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/alloc.rs:185:73: 185:86                                                      
    = note: inside `<std::alloc::Global as std::alloc::Allocator>::allocate` at /home/emilio/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/alloc.rs:245:9: 245:39                              
    = note: inside `alloc::alloc::exchange_malloc` at /home/emilio/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/alloc.rs:334:11: 334:34
    = note: inside `std::boxed::Box::<crossbeam_epoch::sync::queue::Node<crossbeam_epoch::internal::SealedBag>>::new` at /home/emilio/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/boxed.rs:21
7:9: 217:20
    = note: inside `<crossbeam_epoch::sync::queue::Node<crossbeam_epoch::internal::SealedBag> as crossbeam_epoch::atomic::Pointable>::init` at /home/emilio/.cargo/registry/src/index.crates.io-6f17d22bba15001f/crossbeam-epoch-0.9.14/src/
atomic.rs:200:23: 200:37
    = note: inside `crossbeam_epoch::atomic::Owned::<crossbeam_epoch::sync::queue::Node<crossbeam_epoch::internal::SealedBag>>::init` at /home/emilio/.cargo/registry/src/index.crates.io-6f17d22bba15001f/crossbeam-epoch-0.9.14/src/atomic
.rs:1159:35: 1159:48
    = note: inside `crossbeam_epoch::atomic::Owned::<crossbeam_epoch::sync::queue::Node<crossbeam_epoch::internal::SealedBag>>::new` at /home/emilio/.cargo/registry/src/index.crates.io-6f17d22bba15001f/crossbeam-epoch-0.9.14/src/atomic.
rs:1144:9: 1144:25
    = note: inside `crossbeam_epoch::sync::queue::Queue::<crossbeam_epoch::internal::SealedBag>::push` at /home/emilio/.cargo/registry/src/index.crates.io-6f17d22bba15001f/crossbeam-epoch-0.9.14/src/sync/queue.rs:99:19: 102:11
    = note: inside `crossbeam_epoch::internal::Global::push_bag` at /home/emilio/.cargo/registry/src/index.crates.io-6f17d22bba15001f/crossbeam-epoch-0.9.14/src/internal.rs:190:9: 190:48
    = note: inside `crossbeam_epoch::internal::Local::finalize` at /home/emilio/.cargo/registry/src/index.crates.io-6f17d22bba15001f/crossbeam-epoch-0.9.14/src/internal.rs:515:13: 516:65
    = note: inside `crossbeam_epoch::internal::Local::release_handle` at /home/emilio/.cargo/registry/src/index.crates.io-6f17d22bba15001f/crossbeam-epoch-0.9.14/src/internal.rs:498:13: 498:28
    = note: inside `<crossbeam_epoch::collector::LocalHandle as std::ops::Drop>::drop` at /home/emilio/.cargo/registry/src/index.crates.io-6f17d22bba15001f/crossbeam-epoch-0.9.14/src/collector.rs:101:13: 101:48
    = note: inside `std::ptr::drop_in_place::<crossbeam_epoch::collector::LocalHandle> - shim(Some(crossbeam_epoch::collector::LocalHandle))` at /home/emilio/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/libra
ry/core/src/ptr/mod.rs:497:1: 497:56
    = note: inside `std::ptr::drop_in_place::<std::option::Option<crossbeam_epoch::collector::LocalHandle>> - shim(Some(std::option::Option<crossbeam_epoch::collector::LocalHandle>))` at /home/emilio/.rustup/toolchains/nightly-x86_64-un
known-linux-gnu/lib/rustlib/src/rust/library/core/src/ptr/mod.rs:497:1: 497:56
    = note: inside `std::mem::drop::<std::option::Option<crossbeam_epoch::collector::LocalHandle>>` at /home/emilio/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/mem/mod.rs:987:24: 987:25
    = note: inside closure at /home/emilio/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sys/common/thread_local/fast_local.rs:243:9: 243:20
    = note: inside `<[closure@std::sys::common::thread_local::fast_local::destroy_value<crossbeam_epoch::collector::LocalHandle>::{closure#0}] as std::ops::FnOnce<()>>::call_once - shim` at /home/emilio/.rustup/toolchains/nightly-x86_64
-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:250:5: 250:71
    = note: inside `<std::panic::AssertUnwindSafe<[closure@std::sys::common::thread_local::fast_local::destroy_value<crossbeam_epoch::collector::LocalHandle>::{closure#0}]> as std::ops::FnOnce<()>>::call_once` at /home/emilio/.rustup/to
olchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/panic/unwind_safe.rs:271:9: 271:19
    = note: inside `std::panicking::r#try::do_call::<std::panic::AssertUnwindSafe<[closure@std::sys::common::thread_local::fast_local::destroy_value<crossbeam_epoch::collector::LocalHandle>::{closure#0}]>, ()>` at /home/emilio/.rustup/t
oolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/panicking.rs:500:40: 500:43
    = note: inside `std::panicking::r#try::<(), std::panic::AssertUnwindSafe<[closure@std::sys::common::thread_local::fast_local::destroy_value<crossbeam_epoch::collector::LocalHandle>::{closure#0}]>>` at /home/emilio/.rustup/toolchains
/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/panicking.rs:464:19: 464:81
    = note: inside `std::panic::catch_unwind::<std::panic::AssertUnwindSafe<[closure@std::sys::common::thread_local::fast_local::destroy_value<crossbeam_epoch::collector::LocalHandle>::{closure#0}]>, ()>` at /home/emilio/.rustup/toolcha
ins/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/panic.rs:142:14: 142:33
    = note: inside `std::sys::common::thread_local::fast_local::destroy_value::<crossbeam_epoch::collector::LocalHandle>` at /home/emilio/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sys/commo
n/thread_local/fast_local.rs:240:21: 244:8
    = note: inside `std::sys_common::thread_local_dtor::register_dtor_fallback::run_dtors` at /home/emilio/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sys_common/thread_local_dtor.rs:43:17: 4
3:26
[...]

And so on.

[emilio]

Valgrind doesn't report the same:

$ valgrind /home/emilio/src/moz/rayon/target/debug/deps/scoped_threadpool-42ac87d907424fc2                                                                                                                                               
==48462== Memcheck, a memory error detector
==48462== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==48462== Using Valgrind-3.21.0 and LibVEX; rerun with -h for copyright info
==48462== Command: /home/emilio/src/moz/rayon/target/debug/deps/scoped_threadpool-42ac87d907424fc2
==48462== 

running 3 tests
test missing_scoped_tls ... ok
test build_scoped_tls_threadpool ... ok
test spawn_scoped_tls_threadpool ... ok

test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.85s

==48462== 
==48462== HEAP SUMMARY:
==48462==     in use at exit: 186,440 bytes in 91 blocks
==48462==   total heap usage: 2,060 allocs, 1,969 frees, 693,322 bytes allocated
==48462== 
==48462== LEAK SUMMARY:
==48462==    definitely lost: 0 bytes in 0 blocks
==48462==    indirectly lost: 0 bytes in 0 blocks
==48462==      possibly lost: 84,160 bytes in 40 blocks
==48462==    still reachable: 102,280 bytes in 51 blocks
==48462==         suppressed: 0 bytes in 0 blocks
==48462== Rerun with --leak-check=full to see details of leaked memory
==48462== 
==48462== For lists of detected and suppressed errors, rerun with: -s
==48462== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

So maybe a miri false-positive?

[emilio]

==48961== 39,976 bytes in 19 blocks are possibly lost in loss record 4 of 6
==48961==    at 0x4841848: malloc (vg_replace_malloc.c:431)
==48961==    by 0x1DC7CC: alloc (alloc.rs:102)
==48961==    by 0x1DC7CC: alloc::alloc::Global::alloc_impl (alloc.rs:185)
==48961==    by 0x1DC566: allocate (alloc.rs:245)
==48961==    by 0x1DC566: alloc::alloc::exchange_malloc (alloc.rs:334)
==48961==    by 0x1DCAF7: new<crossbeam_epoch::internal::Local> (boxed.rs:217)
==48961==    by 0x1DCAF7: <T as crossbeam_epoch::atomic::Pointable>::init (atomic.rs:200)
==48961==    by 0x1E3D36: crossbeam_epoch::atomic::Owned<T>::init (atomic.rs:1159)
==48961==    by 0x1E3D06: crossbeam_epoch::atomic::Owned<T>::new (atomic.rs:1144)
==48961==    by 0x1DE284: crossbeam_epoch::internal::Local::register (internal.rs:321)
==48961==    by 0x1DCC99: crossbeam_epoch::collector::Collector::register (collector.rs:45)
==48961==    by 0x1E018F: crossbeam_epoch::default::HANDLE::__init (default.rs:34)
==48961==    by 0x1E01EB: crossbeam_epoch::default::HANDLE::__getit::{{closure}} (fast_local.rs:103)
==48961==    by 0x1DBB75: std::sys::common::thread_local::lazy::LazyKeyInner<T>::initialize (mod.rs:54)
==48961==    by 0x1DB733: std::sys::common::thread_local::fast_local::Key<T>::try_initialize (fast_local.rs:194)

It seems miri doesn't consider TLS-stored memory as reachable? If you agree with this diagnosis we can probably close this.

[emilio]

I guess this is rust-lang/miri#2881