[GHC] #15595: Stack overflow in withArgs leads to infinite memory-consuming loop
#15595: Stack overflow in withArgs leads to infinite memory-consuming loop --------------------------------------+---------------------------------- Reporter: NeilMitchell | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: | Operating System: Windows Architecture: x86_64 (amd64) | Type of failure: Runtime crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: --------------------------------------+---------------------------------- Given the program: {{{#!hs import System.Environment main :: IO () main = do putStrLn "Starting" withArgs (replicate 1000 "") $ return () }}} When run with: {{{ ghc --make WithArgsBug.hs -rtsopts && WithArgsBug +RTS -K1K }}} The program prints out "Starting", then loops forever, taking 1 CPU core and allocating memory (approx 1Gb per min), until the computer is unresponsive. The program does not respond to Ctrl-C and has to be killed from the task manager. The {{{-K1K}}} flag limits the stack to approx 33Kb. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15595 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15595: Stack overflow in withArgs leads to infinite memory-consuming loop ----------------------------------+-------------------------------------- Reporter: NeilMitchell | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.5 Resolution: | Keywords: Operating System: Windows | Architecture: x86_64 (amd64) Type of failure: Runtime crash | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | ----------------------------------+-------------------------------------- Changes (by osa1): * version: 8.4.3 => 8.5 Comment: I did a little bit of debugging -- basically the RTS is throwing a stack overflow exception, but the mutator is then trying to allocate more stack space (maybe because stack overflow exception is somehow masked?), causing a loop. A different variant of this program exits with a stack overflow exception: {{{#!haskell {-# LANGUAGE ForeignFunctionInterface #-} import Foreign.C.Types import Foreign.C.String import Foreign.C import Foreign.Ptr import GHC.Foreign (withCStringsLen) foreign import ccall unsafe "setProgArgv" c_setProgArgv :: CInt -> Ptr CString -> IO () main :: IO () main = do putStrLn "Starting" withCStringsLen utf8 (replicate 1000 "") $ \len css -> do c_setProgArgv (fromIntegral len) css }}} Output: {{{ $ ./Main +RTS -K1K Starting Main: Stack space overflow: current size 33624 bytes. Main: Use `+RTS -Ksize -RTS' to increase it. }}} I don't know why the `withArgs` version doesn't fail with the same error yet, but I think `Note [Throw to self when masked]` is relevant. (Confirmed on GHC HEAD so updating the version) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15595#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15595: Stack overflow in withArgs leads to infinite memory-consuming loop ----------------------------------+-------------------------------------- Reporter: NeilMitchell | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.5 Resolution: | Keywords: Operating System: Windows | Architecture: x86_64 (amd64) Type of failure: Runtime crash | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | ----------------------------------+-------------------------------------- Comment (by osa1): Right, so this is because the thread is in masked state and stack overflow exception is not actually raised because of this. If I change the program above to this: {{{#!haskell {-# LANGUAGE ForeignFunctionInterface #-} import Foreign.C import Foreign.Ptr import GHC.Foreign (withCStringsLen) import GHC.IO.Encoding (utf8) import Control.Exception (mask_) foreign import ccall unsafe "setProgArgv" c_setProgArgv :: CInt -> Ptr CString -> IO () main :: IO () main = do putStrLn "Starting" mask_ $ withCStringsLen utf8 (replicate 1000 "") $ \len css -> do c_setProgArgv (fromIntegral len) css putStrLn "Done" }}} (only difference is that I added a `mask_`) this also loops. Not sure about what's the right thing to do here ... -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15595#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15595: Stack overflow in withArgs leads to infinite memory-consuming loop ----------------------------------+-------------------------------------- Reporter: NeilMitchell | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.5 Resolution: | Keywords: Operating System: Windows | Architecture: x86_64 (amd64) Type of failure: Runtime crash | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | ----------------------------------+-------------------------------------- Comment (by osa1): The reason why the original code loops while my first example doesn't is because I don't use `getArgs`. `getArgs` calls this function: {{{#!haskell withProgArgv :: [String] -> IO a -> IO a withProgArgv new_args act = do pName <- System.Environment.getProgName existing_args <- System.Environment.getArgs bracket_ (setProgArgv new_args) (setProgArgv (pName:existing_args)) act }}} The `setProgArgv new_args` part is where we get a stack overflow, but it's evaluated in masked state because of `bracket_`: {{{#!haskell bracket_ before after thing = bracket before (const after) (const thing) bracket before after thing = mask $ \restore -> do a <- before r <- restore (thing a) `onException` after a _ <- after a return r }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15595#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15595: Stack overflow in withArgs leads to infinite memory-consuming loop ----------------------------------+-------------------------------------- Reporter: NeilMitchell | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.5 Resolution: | Keywords: Operating System: Windows | Architecture: x86_64 (amd64) Type of failure: Runtime crash | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | ----------------------------------+-------------------------------------- Comment (by osa1): Here's another reproducer: {{{#!haskell import Control.Exception (mask_) main :: IO () main = mask_ (print (foldl (+) 0 [0 .. 1000000])) }}} If you remove `mask_` this fails with stack overflow (add `+RTS -K1K`). With `mask_` it gets stuck in the same loop as the original program. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15595#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15595: Stack overflow in withArgs leads to infinite memory-consuming loop ----------------------------------+-------------------------------------- Reporter: NeilMitchell | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.5 Resolution: | Keywords: Operating System: Windows | Architecture: x86_64 (amd64) Type of failure: Runtime crash | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | ----------------------------------+-------------------------------------- Comment (by simonmar): Isn't this the correct behaviour? StackOverflow is an asynchronous exception, so we can't throw it inside `mask`. I don't understand why the program loops, though. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15595#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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