Don't deadlock when failing to acquire a jobserver token

src/concurrency_limiter.rs

@@ -25,8 +25,18 @@ pub(super) fn new(sess: &Session, pending_jobs: usize) -> Self {
             .clone()
             .into_helper_thread(move |token| {
                 let mut state = state_helper.lock().unwrap();
-                state.add_new_token(token.unwrap());
+                match token {
+                    Ok(token) => {
+                        state.add_new_token(token);
                         available_token_condvar_helper.notify_one();
+                    }
+                    Err(err) => {
+                        state.poison(format!("failed to acquire jobserver token: {}", err));
+                        // Notify all threads waiting for a token to give them a chance to
+                        // gracefully exit.
+                        available_token_condvar_helper.notify_all();
+                    }
+                }
             })
             .unwrap();
         ConcurrencyLimiter {
@@ -37,17 +47,32 @@ pub(super) fn new(sess: &Session, pending_jobs: usize) -> Self {
         }
     }
 
-    pub(super) fn acquire(&mut self) -> ConcurrencyLimiterToken {
+    pub(super) fn acquire(&mut self, handler: &rustc_errors::Handler) -> ConcurrencyLimiterToken {
         let mut state = self.state.lock().unwrap();
         loop {
             state.assert_invariants();
 
-            if state.try_start_job() {
+            match state.try_start_job() {
+                Ok(true) => {
                     return ConcurrencyLimiterToken {
                         state: self.state.clone(),
                         available_token_condvar: self.available_token_condvar.clone(),
                     };
                 }
+                Ok(false) => {}
+                Err(err) => {
+                    // An error happened when acquiring the token. Raise it as fatal error.
+                    // Make sure to drop the mutex guard first to prevent poisoning the mutex.
+                    drop(state);
+                    if let Some(err) = err {
+                        handler.fatal(&err).raise();
+                    } else {
+                        // The error was already emitted, but compilation continued. Raise a silent
+                        // fatal error.
+                        rustc_errors::FatalError.raise();
+                    }
+                }
+            }
 
             self.helper_thread.as_mut().unwrap().request_token();
             state = self.available_token_condvar.wait(state).unwrap();
@@ -100,13 +125,22 @@ pub(super) struct ConcurrencyLimiterState {
         pending_jobs: usize,
         active_jobs: usize,
 
+        poisoned: bool,
+        stored_error: Option<String>,
+
         // None is used to represent the implicit token, Some to represent explicit tokens
         tokens: Vec<Option<Acquired>>,
     }
 
     impl ConcurrencyLimiterState {
         pub(super) fn new(pending_jobs: usize) -> Self {
-            ConcurrencyLimiterState { pending_jobs, active_jobs: 0, tokens: vec![None] }
+            ConcurrencyLimiterState {
+                pending_jobs,
+                active_jobs: 0,
+                poisoned: false,
+                stored_error: None,
+                tokens: vec![None],
+            }
         }
 
         pub(super) fn assert_invariants(&self) {
@@ -127,14 +161,18 @@ pub(super) fn add_new_token(&mut self, token: Acquired) {
             self.drop_excess_capacity();
         }
 
-        pub(super) fn try_start_job(&mut self) -> bool {
+        pub(super) fn try_start_job(&mut self) -> Result<bool, Option<String>> {
+            if self.poisoned {
+                return Err(self.stored_error.take());
+            }
+
             if self.active_jobs < self.tokens.len() {
                 // Using existing token
                 self.job_started();
-                return true;
+                return Ok(true);
             }
 
-            false
+            Ok(false)
         }
 
         pub(super) fn job_started(&mut self) {
@@ -161,6 +199,11 @@ pub(super) fn job_already_done(&mut self) {
             self.assert_invariants();
         }
 
+        pub(super) fn poison(&mut self, error: String) {
+            self.poisoned = true;
+            self.stored_error = Some(error);
+        }
+
         fn drop_excess_capacity(&mut self) {
             self.assert_invariants();
 

src/driver/aot.rs

@@ -407,7 +407,7 @@ pub(crate) fn run_aot(
                                     backend_config.clone(),
                                     global_asm_config.clone(),
                                     cgu.name(),
-                                    concurrency_limiter.acquire(),
+                                    concurrency_limiter.acquire(tcx.sess.diagnostic()),
                                 ),
                                 module_codegen,
                                 Some(rustc_middle::dep_graph::hash_result),