Miri reports possible UB in Body

[jjant]

Context

Recently, I was trying to run miri in our crates in smithy-rs and ran into a Miri failure for this test.

See #3015 for details.

Miri report:

test byte_stream::tests::read_from_channel_body ... error: Undefined Behavior: trying to retag from <462357> for SharedReadWrite permission at alloc190436[0x40], but that tag does not exist in the borrow stack for this location
   --> /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/hyper-0.14.20/src/body/body.rs:566:44
    |
566 |         futures_util::future::poll_fn(|cx| self.poll_ready(cx)).await
    |                                            ^^^^^^^^^^^^^^^^^^^
    |                                            |
    |                                            trying to retag from <462357> for SharedReadWrite permission at alloc190436[0x40], but that tag does not exist in the borrow stack for this location
    |                                            this error occurs as part of two-phase retag at alloc190436[0x28..0x50]
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
    = help: see https:/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
help: <462357> was created by a Unique retag at offsets [0x28..0x50]
   --> aws-smithy-http/src/byte_stream.rs:615:52
    |
615 |             sender.send_data(Bytes::from("data 2")).await.unwrap();
    |                                                    ^^^^^^
help: <462357> was later invalidated at offsets [0x40..0x41] by a read access
   --> aws-smithy-http/src/byte_stream.rs:618:9
    |
618 | /         assert_eq!(
619 | |             byte_stream.collect().await.expect("no errors").into_bytes(),
620 | |             Bytes::from("data 1data 2data 3")
621 | |         );
    | |__________^
    = note: BACKTRACE:
    = note: inside closure at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/hyper-0.14.20/src/body/body.rs:566:44
    = note: inside `<futures_util::future::poll_fn::PollFn<[closure@hyper::body::Sender::ready::{closure#0}::{closure#0}]> as futures_core::Future>::poll` at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-util-0.3.24/src/future/poll_fn.rs:56:9
    = note: inside closure at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/hyper-0.14.20/src/body/body.rs:566:64
    = note: inside `<std::future::from_generator::GenFuture<[static generator@hyper::body::Sender::ready::{closure#0}]> as futures_core::Future>::poll` at /Users/jjantdev/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/future/mod.rs:91:19
    = note: inside closure at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/hyper-0.14.20/src/body/body.rs:571:21
    = note: inside `<std::future::from_generator::GenFuture<[static generator@hyper::body::Sender::send_data::{closure#0}]> as futures_core::Future>::poll` at /Users/jjantdev/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/future/mod.rs:91:19
note: inside closure at aws-smithy-http/src/byte_stream.rs:615:52
   --> aws-smithy-http/src/byte_stream.rs:615:52
    |
615 |             sender.send_data(Bytes::from("data 2")).await.unwrap();
    |                                                    ^^^^^^
    = note: inside `<std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:613:33: 617:10]> as futures_core::Future>::poll` at /Users/jjantdev/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/future/mod.rs:91:19
    = note: inside closure at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/task/core.rs:184:17
    = note: inside `tokio::loom::std::unsafe_cell::UnsafeCell::<tokio::runtime::task::core::Stage<std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:613:33: 617:10]>>>::with_mut::<std::task::Poll<()>, [closure@tokio::runtime::task::core::CoreStage<std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:613:33: 617:10]>>::poll::{closure#0}]>` at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/loom/std/unsafe_cell.rs:14:9
    = note: inside `tokio::runtime::task::core::CoreStage::<std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:613:33: 617:10]>>::poll` at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/task/core.rs:174:13
    = note: inside closure at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/task/harness.rs:480:19
    = note: inside `<std::panic::AssertUnwindSafe<[closure@tokio::runtime::task::harness::poll_future<std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:613:33: 617:10]>, std::sync::Arc<tokio::runtime::scheduler::current_thread::Shared>>::{closure#0}]> as std::ops::FnOnce<()>>::call_once` at /Users/jjantdev/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/panic/unwind_safe.rs:271:9
    = note: inside `std::panicking::r#try::do_call::<std::panic::AssertUnwindSafe<[closure@tokio::runtime::task::harness::poll_future<std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:613:33: 617:10]>, std::sync::Arc<tokio::runtime::scheduler::current_thread::Shared>>::{closure#0}]>, std::task::Poll<()>>` at /Users/jjantdev/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/std/src/panicking.rs:483:40
    = note: inside `std::panicking::r#try::<std::task::Poll<()>, std::panic::AssertUnwindSafe<[closure@tokio::runtime::task::harness::poll_future<std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:613:33: 617:10]>, std::sync::Arc<tokio::runtime::scheduler::current_thread::Shared>>::{closure#0}]>>` at /Users/jjantdev/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/std/src/panicking.rs:447:19
    = note: inside `std::panic::catch_unwind::<std::panic::AssertUnwindSafe<[closure@tokio::runtime::task::harness::poll_future<std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:613:33: 617:10]>, std::sync::Arc<tokio::runtime::scheduler::current_thread::Shared>>::{closure#0}]>, std::task::Poll<()>>` at /Users/jjantdev/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/std/src/panic.rs:137:14
    = note: inside `tokio::runtime::task::harness::poll_future::<std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:613:33: 617:10]>, std::sync::Arc<tokio::runtime::scheduler::current_thread::Shared>>` at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/task/harness.rs:468:18
    = note: inside `tokio::runtime::task::harness::Harness::<std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:613:33: 617:10]>, std::sync::Arc<tokio::runtime::scheduler::current_thread::Shared>>::poll_inner` at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/task/harness.rs:104:27
    = note: inside `tokio::runtime::task::harness::Harness::<std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:613:33: 617:10]>, std::sync::Arc<tokio::runtime::scheduler::current_thread::Shared>>::poll` at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/task/harness.rs:57:15
    = note: inside `tokio::runtime::task::raw::poll::<std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:613:33: 617:10]>, std::sync::Arc<tokio::runtime::scheduler::current_thread::Shared>>` at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/task/raw.rs:194:5
    = note: inside `tokio::runtime::task::raw::RawTask::poll` at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/task/raw.rs:134:18
    = note: inside `tokio::runtime::task::LocalNotified::<std::sync::Arc<tokio::runtime::scheduler::current_thread::Shared>>::run` at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/task/mod.rs:385:9
    = note: inside closure at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/scheduler/current_thread.rs:564:25
    = note: inside closure at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/coop.rs:102:9
    = note: inside `std::thread::LocalKey::<std::cell::Cell<tokio::coop::Budget>>::try_with::<[closure@tokio::coop::with_budget<(), [closure@tokio::runtime::scheduler::current_thread::CoreGuard<'_>::block_on<std::pin::Pin<&mut std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:610:39: 622:6]>>>::{closure#0}::{closure#3}]>::{closure#0}], ()>` at /Users/jjantdev/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/std/src/thread/local.rs:446:16
    = note: inside `std::thread::LocalKey::<std::cell::Cell<tokio::coop::Budget>>::with::<[closure@tokio::coop::with_budget<(), [closure@tokio::runtime::scheduler::current_thread::CoreGuard<'_>::block_on<std::pin::Pin<&mut std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:610:39: 622:6]>>>::{closure#0}::{closure#3}]>::{closure#0}], ()>` at /Users/jjantdev/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/std/src/thread/local.rs:422:9
    = note: inside `tokio::coop::with_budget::<(), [closure@tokio::runtime::scheduler::current_thread::CoreGuard<'_>::block_on<std::pin::Pin<&mut std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:610:39: 622:6]>>>::{closure#0}::{closure#3}]>` at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/coop.rs:95:5
    = note: inside `tokio::coop::budget::<(), [closure@tokio::runtime::scheduler::current_thread::CoreGuard<'_>::block_on<std::pin::Pin<&mut std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:610:39: 622:6]>>>::{closure#0}::{closure#3}]>` at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/coop.rs:72:5
    = note: inside closure at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/scheduler/current_thread.rs:284:29
    = note: inside `tokio::runtime::scheduler::current_thread::Context::enter::<(), [closure@tokio::runtime::scheduler::current_thread::Context::run_task<(), [closure@tokio::runtime::scheduler::current_thread::CoreGuard<'_>::block_on<std::pin::Pin<&mut std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:610:39: 622:6]>>>::{closure#0}::{closure#3}]>::{closure#0}]>` at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/scheduler/current_thread.rs:349:19
    = note: inside `tokio::runtime::scheduler::current_thread::Context::run_task::<(), [closure@tokio::runtime::scheduler::current_thread::CoreGuard<'_>::block_on<std::pin::Pin<&mut std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:610:39: 622:6]>>>::{closure#0}::{closure#3}]>` at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/scheduler/current_thread.rs:284:9
    = note: inside closure at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/scheduler/current_thread.rs:563:34
    = note: inside closure at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/scheduler/current_thread.rs:595:57
    = note: inside `tokio::macros::scoped_tls::ScopedKey::<tokio::runtime::scheduler::current_thread::Context>::set::<[closure@tokio::runtime::scheduler::current_thread::CoreGuard<'_>::enter<[closure@tokio::runtime::scheduler::current_thread::CoreGuard<'_>::block_on<std::pin::Pin<&mut std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:610:39: 622:6]>>>::{closure#0}], std::option::Option<()>>::{closure#0}], (std::boxed::Box<tokio::runtime::scheduler::current_thread::Core>, std::option::Option<()>)>` at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/macros/scoped_tls.rs:61:9
    = note: inside `tokio::runtime::scheduler::current_thread::CoreGuard::<'_>::enter::<[closure@tokio::runtime::scheduler::current_thread::CoreGuard<'_>::block_on<std::pin::Pin<&mut std::future::from_generator::GenFuture<[static generator@aws-smithy-http/src/byte_stream.rs:610:39: 622:6]>>>::{closure#0}], std::option::Option<()>>` at /Users/jjantdev/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/scheduler/current_thread.rs:595:27
note: inside `byte_stream::tests::read_from_channel_body` at aws-smithy-http/src/byte_stream.rs:618:9
   --> aws-smithy-http/src/byte_stream.rs:618:9
    |
618 | /         assert_eq!(
619 | |             byte_stream.collect().await.expect("no errors").into_bytes(),
620 | |             Bytes::from("data 1data 2data 3")
621 | |         );
    | |__________^
note: inside closure at aws-smithy-http/src/byte_stream.rs:610:11
   --> aws-smithy-http/src/byte_stream.rs:610:11
    |
609 |       #[tokio::test]
    |       -------------- in this procedural macro expansion
610 |       async fn read_from_channel_body() {
    |  ___________^
611 | |         let (mut sender, body) = hyper::Body::channel();
612 | |         let byte_stream = Inner::new(body);
613 | |         tokio::spawn(async move {
...   |
621 | |         );
622 | |     }
    | |_____^
    = note: this error originates in the attribute macro `::core::prelude::v1::test` which comes from the expansion of the attribute macro `tokio::test` (in Nightly builds, run with -Z macro-backtrace for more info)

Description

I ported our failing test into Hyper to investigate the issue.

[LucioFranco]

Can merge after that one change thanks for adding this! We probably want to find the fix before we break hyper but this is a great repro.

[Darksonn]

The Body type is Unpin so it doesn't make sense to pin it.

[seanmonstar]

Seems to be taken care of in #3015