Zubin pushed to branch wip/27657 at Glasgow Haskell Compiler / GHC Commits: 82815637 by Zubin Duggal at 2026-08-12T15:59:46+05:30 ghc-internal: annotateSTM should use catchSTM# rather than catch# A catch# frame inside a transaction breaks retry and async exception delivery. Fixes #27657 - - - - - 7 changed files: - + changelog.d/T27657 - libraries/ghc-internal/src/GHC/Internal/STM.hs - + testsuite/tests/concurrent/should_run/T27657a.hs - + testsuite/tests/concurrent/should_run/T27657a.stdout - + testsuite/tests/concurrent/should_run/T27657b.hs - + testsuite/tests/concurrent/should_run/T27657b.stdout - testsuite/tests/concurrent/should_run/all.T Changes: ===================================== changelog.d/T27657 ===================================== @@ -0,0 +1,8 @@ +section: base +issues: #27657 +synopsis: + Fix ``retry`` and async exception delivery inside a ``catchSTM`` handler +description: + ``catchSTM``\'s ``WhileHandling`` annotation used ``catch#``, leaving an IO + ``CATCH_FRAME`` inside the transaction. Use ``catchSTM#``, which is the + correct way to catch exceptions inside STM. ===================================== libraries/ghc-internal/src/GHC/Internal/STM.hs ===================================== @@ -34,7 +34,7 @@ import GHC.Internal.Exception.Context (ExceptionAnnotation) import GHC.Internal.Exception.Type (WhileHandling(..)) import GHC.Internal.Maybe (Maybe(..)) import GHC.Internal.Prim ( - RealWorld, State#, TVar#, atomically#, catch#, catchRetry#, catchSTM#, + RealWorld, State#, TVar#, atomically#, catchRetry#, catchSTM#, newTVar#, raiseIO#, readTVar#, readTVarIO#, retry#, writeTVar#, ) import GHC.Internal.Prim.PtrEq (sameTVar#) @@ -217,7 +217,7 @@ catchSTM (STM m) handler = STM $ catchSTM# m handler' -- | Execute an 'STM' action, adding the given 'ExceptionContext' -- to any thrown synchronous exceptions. annotateSTM :: forall e a. ExceptionAnnotation e => e -> STM a -> STM a -annotateSTM ann (STM io) = STM (catch# io handler) +annotateSTM ann (STM io) = STM (catchSTM# io handler) -- not catch#, see #27657 where handler se = raiseIO# (addExceptionContext ann se) ===================================== testsuite/tests/concurrent/should_run/T27657a.hs ===================================== @@ -0,0 +1,17 @@ +{-# LANGUAGE ScopedTypeVariables #-} + +-- A `retry` escaping a `catchSTM` handler must reach the enclosing `orElse`. +-- `annotateSTM` wraps the handler, so if it uses the IO `catch#` there is a +-- CATCH_FRAME inside the transaction and `findRetryFrameHelper` trips +-- ASSERT(info->i.type != CATCH_FRAME) on a debug RTS. + +import Control.Exception +import GHC.Conc + +main :: IO () +main = do + r <- atomically $ + catchSTM (throwSTM (ErrorCall "boom")) + (\(_ :: SomeException) -> retry) + `orElse` pure "T27657a: completed" + putStrLn r ===================================== testsuite/tests/concurrent/should_run/T27657a.stdout ===================================== @@ -0,0 +1 @@ +T27657a: completed ===================================== testsuite/tests/concurrent/should_run/T27657b.hs ===================================== @@ -0,0 +1,47 @@ +{-# LANGUAGE ScopedTypeVariables #-} + +-- An async exception delivered while a `catchSTM` handler runs must abort the +-- transaction. If `annotateSTM` wraps the handler in an IO `catch#` then +-- `raiseAsync` stops at that CATCH_FRAME instead of the ATOMICALLY_FRAME and +-- re-raises synchronously; the enclosing transaction then fails validation, +-- is restarted, and the exception is swallowed. +-- +-- The target parks on an MVar inside the handler so that the exception is +-- delivered from the killer's context: the target is not scheduled between the +-- write to `tv` and the delivery, so `schedulePostRunThread` cannot restart the +-- transaction on its own and the outcome is deterministic. + +import Control.Concurrent.MVar +import Control.Exception +import GHC.Conc + +waitParked :: ThreadId -> IO () +waitParked t = do + s <- threadStatus t + case s of + ThreadBlocked BlockedOnMVar -> pure () + _ -> threadDelay 1000 >> waitParked t + +main :: IO () +main = do + tv <- newTVarIO (0 :: Int) + park <- newEmptyMVar + result <- newEmptyMVar + t <- forkIO $ do + r <- try $ atomically $ do + v <- readTVar tv -- puts tv in the outer read set + catchSTM (throwSTM (ErrorCall "boom")) + (\(_ :: SomeException) -> + if v == 0 + then do unsafeIOToSTM (takeMVar park) + pure "handler resumed" + else pure "transaction restarted, exception dropped") + putMVar result (r :: Either SomeException String) + waitParked t -- t is now parked inside the handler + atomically (writeTVar tv 1) -- invalidate t's transaction + killThread t + r <- takeMVar result + putStrLn $ case r of + Left e | Just ThreadKilled <- fromException e -> "T27657b: killThread delivered" + | otherwise -> "T27657b: unexpected exception: " ++ displayException e + Right s -> "T27657b: FAILED, " ++ s ===================================== testsuite/tests/concurrent/should_run/T27657b.stdout ===================================== @@ -0,0 +1 @@ +T27657b: killThread delivered ===================================== testsuite/tests/concurrent/should_run/all.T ===================================== @@ -338,3 +338,8 @@ test('T27105_fail', extra_run_opts('+RTS -C0.2 -RTS'), expect_fail, run_timeout_multiplier(0.05)], multimod_compile_and_run, ['T27105.hs', '']) + +# Frames pushed inside an STM transaction by catchSTM's WhileHandling +# annotation must be STM frames, not IO catch frames (#27657) +test('T27657a', normal, compile_and_run, ['']) +test('T27657b', normal, compile_and_run, ['']) View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/828156370e4efadcc556b47d52c33e68... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/828156370e4efadcc556b47d52c33e68... 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