#7653: incorrect handling of StackOverflow exception in the event manager --------------------------+------------------------------------------------- Reporter: nus | Owner: Type: bug | Status: new Priority: normal | Component: libraries/base Version: 7.7 | Keywords: Os: Linux | Architecture: Unknown/Multiple Failure: Runtime crash | Blockedby: Blocking: | Related: --------------------------+------------------------------------------------- Comment(by nus): `libraries\base\GHC\Event\Manager.hs`, the thunk accummulated in `f'`: {{{ registerTimeout :: EventManager -> Int -> TimeoutCallback -> IO TimeoutKey registerTimeout mgr us cb = do !key <- newUnique (emUniqueSource mgr) if us <= 0 then cb else do now <- getMonotonicTime let expTime = fromIntegral us / 1000000.0 + now -- We intentionally do not evaluate the modified map to WHNF here. -- Instead, we leave a thunk inside the IORef and defer its -- evaluation until mkTimeout in the event loop. This is a -- workaround for a nasty IORef contention problem that causes the -- thread-delay benchmark to take 20 seconds instead of 0.2. atomicModifyIORef (emTimeouts mgr) $ \f -> let f' = (Q.insert key expTime cb) . f in (f', ()) wakeManager mgr return $ TK key }}} is evaluated in `applyEdits`: {{{ step :: EventManager -> TimeoutQueue -> IO (Bool, TimeoutQueue) step mgr@EventManager{..} tq = do (timeout, q') <- mkTimeout tq I.poll emBackend timeout (onFdEvent mgr) state <- readIORef emState state `seq` return (state == Running, q') where -- | Call all expired timer callbacks and return the time to the -- next timeout. mkTimeout :: TimeoutQueue -> IO (Timeout, TimeoutQueue) mkTimeout q = do now <- getMonotonicTime applyEdits <- atomicModifyIORef emTimeouts $ \f -> (id, f) let (expired, q'') = let q' = applyEdits q in q' `seq` Q.atMost now q' sequence_ $ map Q.value expired let timeout = case Q.minView q'' of Nothing -> Forever Just (Q.E _ t _, _) -> -- This value will always be positive since the call -- to 'atMost' above removed any timeouts <= 'now' let t' = t - now in t' `seq` Timeout t' return (timeout, q'') }}} The main `loop :: EventManager -> IO ()` in `cleanup :: EventManager -> IO ()` uses: {{{ closeControl :: Control -> IO () closeControl w = do _ <- c_close . fromIntegral . controlReadFd $ w _ <- c_close . fromIntegral . controlWriteFd $ w #if defined(HAVE_EVENTFD) _ <- c_close . fromIntegral . controlEventFd $ w #else _ <- c_close . fromIntegral . wakeupReadFd $ w _ <- c_close . fromIntegral . wakeupWriteFd $ w #endif return () }}} which doesn't clean up the C side of `newControl :: IO Control`. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7653#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#7653: incorrect handling of StackOverflow exception in the event manager --------------------------+------------------------------------------------- Reporter: nus | Owner: Type: bug | Status: patch Priority: normal | Component: libraries/base Version: 7.7 | Keywords: Os: Linux | Architecture: Unknown/Multiple Failure: Runtime crash | Blockedby: Blocking: | Related: --------------------------+------------------------------------------------- Changes (by nus): * status: new => patch -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7653#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#7653: incorrect handling of StackOverflow exception in the event manager ---------------------------------+------------------------------------------ Reporter: nus | Owner: tibbe Type: bug | Status: patch Priority: normal | Milestone: Component: libraries/base | Version: 7.7 Keywords: | Os: Linux Architecture: Unknown/Multiple | Failure: Runtime crash Difficulty: Unknown | Testcase: Blockedby: | Blocking: Related: | ---------------------------------+------------------------------------------ Changes (by kazu-yamamoto): * cc: kazu@… (added) -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7653#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#7653: incorrect handling of StackOverflow exception in the event manager ---------------------------------+------------------------------------------ Reporter: nus | Owner: tibbe Type: bug | Status: patch Priority: normal | Milestone: Component: libraries/base | Version: 7.7 Keywords: | Os: Linux Architecture: Unknown/Multiple | Failure: Runtime crash Difficulty: Unknown | Testcase: Blockedby: | Blocking: Related: | ---------------------------------+------------------------------------------ Comment(by nus): Replying to [comment:6 kazu-yamamoto]:

First of all, I would like to discuss what is the best behavior when the stack of IO manager overflows. Perhaps the best would be not to cause stack overflows in the manager at all. At least the shutdown should be as gracious as possible.

Note that in the current parallel IO manager, timer manager and IO managers are separated. We should apply this discussion to the timer manager. Sure, the bug report and the patches were made before the new I/O manager merge. The code excerpts above that show how the thunk is accumulated are now only pertinent to 7.4 and 7.6 branches. While I'm not sure how (and if) the situation like this could be reproduced on the current HEAD, the concerns might still be applicable: 1. There're no counterparts for `c_setIOManagerControlFd` and `c_setIOManagerWakeupFd` of `newControl` in `closeControl`; 2. A situation might emerge (again, I'm not sure how, but still) when `wakeManager` would be passed an `EventManager` in the `Finished` state.

A comment to the first patch: even if we set manager's FD to -1, nobody

refers to it. What is the purpose of this patch? The RTS does, please have a look at `ioManagerWakeup` in `rts/posix/Signals.c` (and `wakeUpRts` in `rts/Schedule.c`). -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7653#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#7653: incorrect handling of StackOverflow exception in the event manager ---------------------------------+------------------------------------------ Reporter: nus | Owner: tibbe Type: bug | Status: patch Priority: normal | Milestone: Component: libraries/base | Version: 7.7 Keywords: | Os: Linux Architecture: Unknown/Multiple | Failure: Runtime crash Difficulty: Unknown | Testcase: Blockedby: | Blocking: Related: | ---------------------------------+------------------------------------------ Comment(by nus): I should clarify that the patches were meant for the old I/O manager, that is the one that's currently in the 7.4 and 7.6 branches, and only the 7.6 and pre-merge HEAD builds were validated. The new I/O manager situation needs more insight. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7653#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#7653: incorrect handling of StackOverflow exception in the event manager -----------------------------+---------------------------------------------- Reporter: nus | Owner: tibbe Type: bug | Status: closed Priority: normal | Milestone: 7.8.1 Component: libraries/base | Version: 7.7 Resolution: fixed | Keywords: Os: Linux | Architecture: Unknown/Multiple Failure: Runtime crash | Difficulty: Unknown Testcase: | Blockedby: Blocking: | Related: -----------------------------+---------------------------------------------- Changes (by igloo): * status: patch => closed * resolution: => fixed Comment: Fixed by {{{ commit e843e73690f828498f6e33bb89f47a50c3ab2ac9 Author: Ian Lynagh Date: Sat Jun 8 20:19:59 2013 +0100 IO manager: Edit the timeout queue directly, rather than using an edit list Fixes #7653. }}} -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7653#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler