bjoernager/rust
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Reliably signal coordinator thread on panic during ongoing codegen

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Replace the separate AbortCodegenOnDrop guard by integrating this
functionality into OngoingCodegen (or rather, the Coordinator part
of it). This ensures that we send a CodegenAborted message and
wait for workers to finish even if the panic occurs outside
codegen_crate() (e.g. inside join_codegen()).

This requires some minor changes to the handling of CodegenAborted,
as it can now occur when the main thread is LLVMing rather than
Codegenning.
This commit is contained in:
Nikita Popov 2022-07-25 14:04:26 +02:00
parent 6a1f77dba4
commit b00d0fa0c9
2 changed files with 43 additions and 76 deletions
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61
compiler/rustc_codegen_ssa/src/back/write.rs
View file

@ -37,6 +37,7 @@ use rustc_target::spec::{MergeFunctions, SanitizerSet};
use std::any::Any;
use std::fs;
use std::io;
use std::marker::PhantomData;
use std::mem;
use std::path::{Path, PathBuf};
use std::str;
@ -475,10 +476,13 @@ pub fn start_async_codegen<B: ExtraBackendMethods>(
metadata_module,
crate_info,
coordinator_send,
codegen_worker_receive,
shared_emitter_main,
future: coordinator_thread,
coordinator: Coordinator {
sender: coordinator_send,
future: Some(coordinator_thread),
phantom: PhantomData,
},
output_filenames: tcx.output_filenames(()).clone(),
}
}
@ -1273,6 +1277,7 @@ fn start_executing_work<B: ExtraBackendMethods>(
// work to be done.
while !codegen_done
|| running > 0
|| main_thread_worker_state == MainThreadWorkerState::LLVMing
|| (!codegen_aborted
&& !(work_items.is_empty()
&& needs_fat_lto.is_empty()
@ -1492,7 +1497,6 @@ fn start_executing_work<B: ExtraBackendMethods>(
assert!(!codegen_aborted);
codegen_done = true;
codegen_aborted = true;
assert_eq!(main_thread_worker_state, MainThreadWorkerState::Codegenning);
}
Message::Done { result: Ok(compiled_module), worker_id } => {
free_worker(worker_id);
@ -1539,6 +1543,10 @@ fn start_executing_work<B: ExtraBackendMethods>(
}
}
if codegen_aborted {
return Err(());
}
let needs_link = mem::take(&mut needs_link);
if !needs_link.is_empty() {
assert!(compiled_modules.is_empty());
@ -1828,16 +1836,39 @@ impl SharedEmitterMain {
}
}
pub struct Coordinator<B: ExtraBackendMethods> {
pub sender: Sender<Box<dyn Any + Send>>,
future: Option<thread::JoinHandle<Result<CompiledModules, ()>>>,
// Only used for the Message type.
phantom: PhantomData<B>,
}
impl<B: ExtraBackendMethods> Coordinator<B> {
fn join(mut self) -> std::thread::Result<Result<CompiledModules, ()>> {
self.future.take().unwrap().join()
}
}
impl<B: ExtraBackendMethods> Drop for Coordinator<B> {
fn drop(&mut self) {
if let Some(future) = self.future.take() {
// If we haven't joined yet, signal to the coordinator that it should spawn no more
// work, and wait for worker threads to finish.
drop(self.sender.send(Box::new(Message::CodegenAborted::<B>)));
drop(future.join());
}
}
}
pub struct OngoingCodegen<B: ExtraBackendMethods> {
pub backend: B,
pub metadata: EncodedMetadata,
pub metadata_module: Option<CompiledModule>,
pub crate_info: CrateInfo,
pub coordinator_send: Sender<Box<dyn Any + Send>>,
pub codegen_worker_receive: Receiver<Message<B>>,
pub shared_emitter_main: SharedEmitterMain,
pub future: thread::JoinHandle<Result<CompiledModules, ()>>,
pub output_filenames: Arc<OutputFilenames>,
pub coordinator: Coordinator<B>,
}
impl<B: ExtraBackendMethods> OngoingCodegen<B> {
@ -1845,8 +1876,7 @@ impl<B: ExtraBackendMethods> OngoingCodegen<B> {
let _timer = sess.timer("finish_ongoing_codegen");
self.shared_emitter_main.check(sess, true);
let future = self.future;
let compiled_modules = sess.time("join_worker_thread", || match future.join() {
let compiled_modules = sess.time("join_worker_thread", || match self.coordinator.join() {
Ok(Ok(compiled_modules)) => compiled_modules,
Ok(Err(())) => {
sess.abort_if_errors();
@ -1894,26 +1924,13 @@ impl<B: ExtraBackendMethods> OngoingCodegen<B> {
// These are generally cheap and won't throw off scheduling.
let cost = 0;
submit_codegened_module_to_llvm(&self.backend, &self.coordinator_send, module, cost);
submit_codegened_module_to_llvm(&self.backend, &self.coordinator.sender, module, cost);
}
pub fn codegen_finished(&self, tcx: TyCtxt<'_>) {
self.wait_for_signal_to_codegen_item();
self.check_for_errors(tcx.sess);
drop(self.coordinator_send.send(Box::new(Message::CodegenComplete::<B>)));
}
/// Consumes this context indicating that codegen was entirely aborted, and
/// we need to exit as quickly as possible.
///
/// This method blocks the current thread until all worker threads have
/// finished, and all worker threads should have exited or be real close to
/// exiting at this point.
pub fn codegen_aborted(self) {
// Signal to the coordinator it should spawn no more work and start
// shutdown.
drop(self.coordinator_send.send(Box::new(Message::CodegenAborted::<B>)));
drop(self.future.join());
drop(self.coordinator.sender.send(Box::new(Message::CodegenComplete::<B>)));
}
pub fn check_for_errors(&self, sess: &Session) {

58
compiler/rustc_codegen_ssa/src/base.rs
View file

@ -39,7 +39,6 @@ use rustc_target::abi::{Align, VariantIdx};
use std::collections::BTreeSet;
use std::convert::TryFrom;
use std::ops::{Deref, DerefMut};
use std::time::{Duration, Instant};
use itertools::Itertools;
@ -583,7 +582,6 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
metadata_module,
codegen_units.len(),
);
let ongoing_codegen = AbortCodegenOnDrop::<B>(Some(ongoing_codegen));
// Codegen an allocator shim, if necessary.
//
@ -704,7 +702,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
submit_codegened_module_to_llvm(
&backend,
&ongoing_codegen.coordinator_send,
&ongoing_codegen.coordinator.sender,
module,
cost,
);
@ -714,7 +712,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
submit_pre_lto_module_to_llvm(
&backend,
tcx,
&ongoing_codegen.coordinator_send,
&ongoing_codegen.coordinator.sender,
CachedModuleCodegen {
name: cgu.name().to_string(),
source: cgu.previous_work_product(tcx),
@ -725,7 +723,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
CguReuse::PostLto => {
submit_post_lto_module_to_llvm(
&backend,
&ongoing_codegen.coordinator_send,
&ongoing_codegen.coordinator.sender,
CachedModuleCodegen {
name: cgu.name().to_string(),
source: cgu.previous_work_product(tcx),
@ -752,55 +750,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
}
ongoing_codegen.check_for_errors(tcx.sess);
ongoing_codegen.into_inner()
}
/// A curious wrapper structure whose only purpose is to call `codegen_aborted`
/// when it's dropped abnormally.
///
/// In the process of working on rust-lang/rust#55238 a mysterious segfault was
/// stumbled upon. The segfault was never reproduced locally, but it was
/// suspected to be related to the fact that codegen worker threads were
/// sticking around by the time the main thread was exiting, causing issues.
///
/// This structure is an attempt to fix that issue where the `codegen_aborted`
/// message will block until all workers have finished. This should ensure that
/// even if the main codegen thread panics we'll wait for pending work to
/// complete before returning from the main thread, hopefully avoiding
/// segfaults.
///
/// If you see this comment in the code, then it means that this workaround
/// worked! We may yet one day track down the mysterious cause of that
/// segfault...
struct AbortCodegenOnDrop<B: ExtraBackendMethods>(Option<OngoingCodegen<B>>);
impl<B: ExtraBackendMethods> AbortCodegenOnDrop<B> {
fn into_inner(mut self) -> OngoingCodegen<B> {
self.0.take().unwrap()
}
}
impl<B: ExtraBackendMethods> Deref for AbortCodegenOnDrop<B> {
type Target = OngoingCodegen<B>;
fn deref(&self) -> &OngoingCodegen<B> {
self.0.as_ref().unwrap()
}
}
impl<B: ExtraBackendMethods> DerefMut for AbortCodegenOnDrop<B> {
fn deref_mut(&mut self) -> &mut OngoingCodegen<B> {
self.0.as_mut().unwrap()
}
}
impl<B: ExtraBackendMethods> Drop for AbortCodegenOnDrop<B> {
fn drop(&mut self) {
if let Some(codegen) = self.0.take() {
codegen.codegen_aborted();
}
}
ongoing_codegen
}
impl CrateInfo {