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--fix hangs with parallel rustc #140093

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matthiaskrgr opened this issue Apr 20, 2025 · 2 comments
Open

--fix hangs with parallel rustc #140093

matthiaskrgr opened this issue Apr 20, 2025 · 2 comments
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C-bug Category: This is a bug. WG-compiler-parallel Working group: Parallelizing the compiler

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@matthiaskrgr
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repro:

git clone https://github.com/rust-lang/rust-analyzer
cd rust-analyzer
git checkout 723121e5958cf282db3fdb06970776724a7326d5
RUSTFLAGS="-Zthreads=2" cargo clippy --fix    -- -Aclippy::all  -Wclippy::clone_on_copy

At some point there will be no more progress during the builds, it looks like we get stuck on build.rs scripts?
Works fine without the -Zthreads=2 and also works fine without the --fix

What is weird that we don't seem to hang with active cpu load, but I can still see some rustc processes running

rustc 1.88.0-nightly (077cedc2a 2025-04-19)
binary: rustc
commit-hash: 077cedc2afa8ac0b727b7a6cbe012940ba228deb
commit-date: 2025-04-19
host: x86_64-unknown-linux-gnu
release: 1.88.0-nightly
LLVM version: 20.1.2
@matthiaskrgr matthiaskrgr added the C-bug Category: This is a bug. label Apr 20, 2025
@rustbot rustbot added the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Apr 20, 2025
@matthiaskrgr matthiaskrgr added WG-compiler-parallel Working group: Parallelizing the compiler and removed needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. labels Apr 20, 2025
@matthiaskrgr
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also reproducible on stable rustc 1.86.0

@matthiaskrgr matthiaskrgr changed the title clippy --fix hangs with parallel rustc --fix hangs with parallel rustc Apr 20, 2025
@matthiaskrgr
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also happens with just RUSTFLAGS="-Zthreads=2" cargo fix 🤔

@Zoxc Zoxc mentioned this issue Apr 22, 2025
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bors added a commit to rust-lang-ci/rust that referenced this issue Apr 22, 2025
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Auto merge of rust-lang#140145 - Zoxc:job-server-proxy, r=<try>
c4cd906 
Add a jobserver proxy to ensure at least one token is always held

This adds a jobserver proxy to ensure at least one token is always held by `rustc`. Currently with `-Z threads` `rustc` can temporarily give up all its tokens, causing `cargo` to spawn additional `rustc` instances beyond the job limit.

The current behavior causes an issue with `cargo fix` which has a global lock preventing concurrent `rustc` instances, but it also holds a jobserver token, causing a deadlock when `rustc` gives up its token. That is fixed by this PR.

Fixes rust-lang#133873 and rust-lang#140093.
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Labels
C-bug Category: This is a bug. WG-compiler-parallel Working group: Parallelizing the compiler
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