Document Error::{new,other} as to be avoided in pre_exec

[purplesyringa]

This is a mistake I've found in many projects on GitHub and made myself. It's obvious that Error::new/Error::other allocate when you look at their signatures, and it's obvious that the pre_exec closure shouldn't allocate, but when you're asked to write a closure that returns a specific type, you don't expect its main constructor to be problematic.

I've included the list of 71 affected projects in a spoiler, though I don't expect anyone to look through it closely. It includes popular projects like alacritty, pika-backup, rio, rpm-ostree, and headcrab, as well as many smaller ones. For the most part, the snippets I've found are careful to only call functions from libc, nix, or rustix, so it's not a case of general incompetence, but something that just slipped through the cracks.

This docs section is already cluttered, so I've kept it terse.

If this is merged, I'd like to mass-post issues to the affected projects linking to this PR as a centralized source of information and place for discussion. Are there any objections about that?

@rustbot label +A-docs +A-process +O-unix +T-libs-api

List of affected projects

Format: links (witness of multi-threading)

• https://github.com/0x4D44/mdmcp/blob/cccdfab32d5a203d03ccbc6ed261a2f4a4e6420d/mdmcpsrvr/src/sandbox.rs#L385 (tokio::main)
• https://github.com/alacritty/alacritty/blob/bf68154f9e4b91e5ba21dfb8151dbde23c46d47d/alacritty_terminal/src/tty/unix.rs#L250 (thread::spawn)
• https://github.com/AsterZephyr/polyagent/blob/6a7f5aced0335926941931ca965e5455890a7ce3/rust/agent-core/src/sandbox.rs#L257 (tokio::main)
• https://github.com/bootc-dev/containers-image-proxy-rs/blob/68673c836a91070811c17858183266e634f9719d/src/imageproxy.rs#L285 (library)
• https://github.com/delft-hyperloop/DH09-sw/blob/27f489edd297e9b93b8caa2c0b222ae8a9f1a70f/gs/station/src/tui/app.rs#L69 (thread::spawn)
• https://github.com/fcoury/oxproc/blob/85e8b510102d1caf7f15fd88694b4ad24bcd59b7/src/manager.rs#L55 (tokio::runtime::Builder::new_multi_thread)
• https://github.com/galqiwi/runner/blob/35d4756bc518b5947e0275e4251b674c8c354b62/src/run.rs#L75 (tokio::main)
• https://github.com/golemfactory/yagna/blob/31f5353e5532e947abb824adc30791583d01bf74/golem_cli/src/command/yagna.rs#L384, https://github.com/golemfactory/yagna/blob/31f5353e5532e947abb824adc30791583d01bf74/test-utils/test-framework/src/yagna.rs#L103 (actix_rt::main)
• https://github.com/greshake/i3status-rust/blob/2d797c50702873fc8efe518156e204a0b3979fc8/src/subprocess.rs#L14 (thread::Builder::new)
• https://github.com/hattmo/projects/blob/626feea965cebd90490e3e16f2c4b0c6725212e1/opstation/src/manager/mod.rs#L50 (none)
• https://github.com/iamazy/nxshell/blob/ca3b94324831cdc8f8b533c1ff252bdeeba3acbf/crates/alacritty_terminal/src/tty/unix.rs#L256 (thread::spawn)
• https://github.com/ironcore-dev/FeOS/blob/9dee27162f5860991dc176bf2e0d9f948dc97d5b/feos/services/vm-service/src/vmm/ch_adapter.rs#L272 (tokio::main)
• https://github.com/jamesmcm/vopono/blob/d1aad75d9fc8959488e020f3ffea6ffd1f798609/vopono_core/src/network/application_wrapper.rs#L193 (thread::spawn)
• https://github.com/Kocoro-lab/Shannon/blob/05b0c5ca7b65b2d2c2c8be83906b37d5307718e7/rust/agent-core/src/sandbox.rs#L261 (tokio::main)
• https://github.com/kolloch/zack/blob/2244f29a74f74401abd8869c50c7d868afd656b9/zaun/src/lib.rs#L157 (library)
• https://github.com/MaxVerevkin/wlr-which-key/blob/179261a45867544f2b3c25871b8ef77c6f9bdf43/src/main.rs#L532 (none)
• https://github.com/openanolis/cryptpilot/blob/8deab3eee1d6488f6578f6284d0494c70ce7f6b4/src/provider/mod.rs#L228 (tokio::main)
• https://github.com/pantsbuild/pants/blob/e5ee289fc67a02a8d011f3fd160e8544727bd613/src/rust/process_execution/children/src/lib.rs#L44 (tokio::main)
• https://github.com/pika-backup/pika-backup/blob/297d21a2b02dc7230c2d8e7cf86289d25ba82de1/pika-backup/src/utils.rs#L171 (library)
• https://github.com/proxmox/pve-xtermjs/blob/1c92330cccb21fb65abcff6e35848b712592dccb/termproxy/src/main.rs#L290 (none)
• https://github.com/rand/mnemosyne/blob/3db85ed0bde68f25c38fb4a77c6cac50fa638d52/src/daemon/mod.rs#L181, https://github.com/rand/mnemosyne/blob/3db85ed0bde68f25c38fb4a77c6cac50fa638d52/src/daemon/orchestration.rs#L204 (tokio::main)
• https://github.com/raphamorim/rio/blob/c0d687a3a1a439dbe81405d805c3dc191c90c45f/teletypewriter/src/unix/mod.rs#L551 (library)
• https://github.com/rawkode/cuenv/blob/2e76ab93b0faa25a53094406e7f5f1ca15e32068/crates/security/src/access_restrictions.rs#L379 (thread::spawn)
• https://github.com/reubeno/brush/blob/b1a76480bf000bb2d351b65c2012eb06f88fa0ae/brush-core/src/sys/unix/commands.rs#L64 (tokio::runtime::Runtime::new())
• https://github.com/sebosp/chartacritty/blob/b2c19ee7836ca3d939fff045cad93182749cc0ea/alacritty_terminal/src/tty/unix.rs#L250 (thread::spawn)
• https://github.com/skanehira/ghost/blob/ad500f9fb47b7266e6d5989b0232881efe1bfa87/src/app/process.rs#L82 (tokio::main)
• https://github.com/coreos/rpm-ostree/blob/0ad2ee53f3c2d77bc4adfd618d865e919c943865/rust/src/bwrap.rs#L100 (thread::spawn)
• https://github.com/zerocore-ai/microsandbox/blob/9d334572a821775070de68d7cb20f1b2b65da9c3/microsandbox-utils/lib/runtime/supervisor.rs#L131 (tokio::main)
• https://github.com/willfindlay/bpfcontain-rs/blob/eb2cd826b609e165d63d784c0f562b7a278171d2/src/subcommands/run.rs#L62 (library)
• https://github.com/willothy/sesh/blob/c013dda71e69d59de3e23c08aa7fc4f71c8e087c/shared/src/pty.rs#L216 (tokio::main)
• https://github.com/AiTerminalFoundation/ai-terminal/blob/33618aedf66229ee5075519640344fef44b058e1/ai-terminal/src-tauri/src/command/core/execute_command.rs#L388 (thread::spawn)
• https://github.com/Toromino/chromiumos-platform2/blob/97e6ba18f0e5ab6723f3448a66f82c1a07538d87/os_install_service/src/util.rs#L92 (thread::spawn)
• https://github.com/jimmyff/nixfiles/blob/462d487680d91b25a74f69ce2509e519504ea5de/scripts/flitter/flitter.rs#L455 (tokio::main)
• https://github.com/simonrw/dap-gui/blob/5d073ff0ea4e99ba94af6c0137c089418ead5298/crates/server/src/debugpy.rs#L43 (thread::spawn)
• https://github.com/Team-Atlanta/aixcc-afc-atlantis/blob/ef3425da2bc8951afcfe419913e88b064eb3bcf0/example-crs-webservice/crs-multilang/uniafl/src/concolic/executor/symcc/symcc.rs#L216, https://github.com/Team-Atlanta/aixcc-afc-atlantis/blob/ef3425da2bc8951afcfe419913e88b064eb3bcf0/example-crs-webservice/crs-multilang/uniafl/src/concolic/executor/symcc/symqemu.rs#L259 (thread::spawn)
• https://github.com/nullpo-head/dbgee/blob/e2a34f3271ee7e100eeccd8e00f8a50729ef0f1a/dbgee/src/os/linux.rs#L162 (thread::spawn)
• https://github.com/KingBright/training_manager/blob/22e54166ed4e153e05b6902d7d8661a6a4b5e31a/src/task_manager.rs#L87 (tokio::main)
• https://github.com/SparkyTD/ovpn/blob/c55e2945776ab0da0616707315141a5a04c4129c/ovpnd/src/session_manager.rs#L32 (tokio::main)
• https://github.com/FulanXisen/like/blob/e5b6543e8f1729e410439e1e50ceed1fdc9fddc2/like-strace/src/main.rs#L51 (none)
• https://github.com/patrickdappollonio/dotenv/blob/5ec161045b21c5548f867cae637bea64bea59550/src/main.rs#L166 (none)
• https://github.com/jefflouisma/KasmVNCPlus/blob/765a77371645cbbba5b639f49591c251aa97f363/novnc_recorder/src/ffmpeg.rs#L11 (thread::spawn)
• https://github.com/xlsynth/xlsynth-crate/blob/02967d938910cf23a09e93ffb3284e50c1e11d7d/xlsynth-driver/src/prover.rs#L474 (thread::spawn)
• https://github.com/M00NLIG7/pandoras_box/blob/d2dcfff230426688af6d6770899d9865d27b5733/rustrc/src/stateful_process.rs#L37 (tokio::main)
• https://github.com/bendiksolheim/term/blob/9906f5c5a0115fc330ac6c56e947d41c4ad78545/src/term/term.rs#L155 (async_std::task::spawn)
• https://github.com/yskszk63/ssssh/blob/9c03e1d7bab2b1cdc52892d4c28e11daf639bd94/examples/bash.rs#L87 (tokio::main)
• https://github.com/jarhodes314/tcp-buffer-test/blob/63c366f5c1dd940f9a392fc73be653c0c0d81b4c/src/main.rs#L281 (tokio::main)
• https://github.com/luser/spawn-ptrace/blob/d29c538c0c81ac1d62f19cee8be48e4ab0926392/src/lib.rs#L59 (library)
• https://github.com/OSH-2020/x-chital/blob/fadcc96868b619f4463c95edd01b71f23fb20c13/rvisor/src/sentry/platform/ptrace.rs#L21 (none)
• https://github.com/sbstp/supermon/blob/3353fad862970eb54c293c63dda9980539e1ac0b/src/reactor.rs#L76 (thread::spawn)
• https://github.com/headcrab-rs/headcrab/blob/5a420c5da3f51196cd991680bb2b3fded6ce7033/src/target/unix.rs#L55 (library)
• https://github.com/taoky/greenhook/blob/2a69aa432ab7fd4eee68eea2a2b4dbec845165cc/src/lib.rs#L430 (thread::spawn)
• https://github.com/saltnpepper97/snug/blob/b59df7f112f059f144c7a32c00bd8ad73a7d584d/src/process.rs#L89 (thread::spawn)
• https://github.com/regiontog/WebDM/blob/43b557295316668a975466354d86703f7ad3dd2d/src/main.rs#L488 (gtk)
• https://github.com/KailasMahavarkar/rustbox/blob/c27801cc479c75fec6c12a08272d507793769871/rustbox/src/executor.rs#L226 (thread::spawn)
• https://github.com/roboplc/virtual-terminal/blob/967e6c9dea5455c7f7f3b9276b88abb445009a3a/src/lib.rs#L224 (library)
• https://github.com/nui/caco3/blob/ce093f81c6a57dd9172894e7d5ab28d2984f5cc8/caco3-pty/src/nixpty.rs#L67 (library)
• https://github.com/nohackjustnoobb/Macro-Deck-Driver/blob/531421e41266ca952cf7c62644da0194877c1e24/src/cli/background_start.rs#L69 (thread::spawn)
• https://github.com/ManishaChavva/a653rs-linux/blob/1b2830594519d9eff3779f6cd22795dbe14f8d54/hypervisor/src/hypervisor/partition.rs#L258 (thread::spawn)
• https://github.com/rhinos0608/codecrucible-synth/blob/7c7d5fb7743116a2a94c3156dee43439675a4e2e/rust-executor/src/executors/command.rs#L422 (library)
• https://github.com/Nughm3/sandbox/blob/5146a95e29b198b85c496077dc096bbe1e882d23/src/lib.rs#L73 (library)
• https://github.com/naverwhale/whaleos-platform2/blob/166e825c8a43753dda3b021c5519124842d1d8d5/os_install_service/src/util.rs#L92 (thread::spawn)
• https://github.com/de-vri-es/webterm-server-rs/blob/69845f7f0678dce942de8313d6d4b0a57f83a9a9/src/pty/pseudo_terminal_pair.rs#L59, https://github.com/de-vri-es/webterm-server-rs/blob/69845f7f0678dce942de8313d6d4b0a57f83a9a9/src/pty/pseudo_terminal_pair.rs#L63 (tokio::main)
• https://github.com/jjs-dev/jjs/blob/bf00423f70f8a6ed508bbcb8b38840225e43cc73/src/invoker/src/worker/valuer.rs#L39 (tokio::main)
• https://github.com/Drumblow/seac/blob/9c9fea1222ab98aee25376b51de8a66fe0eb4676/src/executor/process_manager.rs#L139 (tokio::main)
• https://github.com/CJacob314/rustcon/blob/92c582fa21fc68bb8740f617455820c3377a0274/src/main.rs#L166 (none)
• https://github.com/antialize/simple-admin/blob/cbde17d1b132be8427340fcc55f82958641d32a6/src/bin/sadmin/persist_daemon.rs#L223 (tokio::main)
• https://github.com/jonathanforhan/pty-exec/blob/c08b037747aa049cd7d41d6ea8de02305775d789/src/unix/pty.rs#L48 (library)
• https://github.com/0b01/tail2/blob/5f699b6aafb4c5be677c21e8f619c35bca33efcf/tail2/src/client/run.rs#L178 (tokio::main)
• https://github.com/owtaylor/ttymon/blob/61dfc842151c1e45920c427471617cbb27caff0d/src/pty.rs#L187 (none)
• https://github.com/Nughm3/contest-platform/blob/25a6ad7ff84550f5a2b32f270660acdd010e5a93/judge/src/sandbox.rs#L96 (tokio::main)
• https://github.com/valoq/glycin/blob/3447555afb60245f4e2329f129c921573f077d1b/glycin/src/sandbox.rs#L335 (library)

[rustbot]

r? @Mark-Simulacrum

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Use r? to explicitly pick a reviewer

[Mark-Simulacrum]

@bors r+ rollup

[bors]

📌 Commit 33a6142 has been approved by Mark-Simulacrum

It is now in the queue for this repository.

[jhpratt]

still in queue

@bors r-

[cgwalters]

This text is technically correct. However in practice at least glibc it's always been safe to malloc() after fork() because it's careful to acquire the malloc mutex before fork returns.

[purplesyringa]

Yes, that's true. But there have previously been related issues on macOS and with jemalloc, IIRC, so at least it's not universal. I don't think we should recommend something that isn't guaranteed to work in the docs. If someone wants to break the rules, that becomes their responsibility.