Race condition in setNumCapabilities
|Reported by:||akio||Owned by:||simonmar|
|Operating System:||Unknown/Multiple||Architecture:||x86_64 (amd64)|
|Type of failure:||Runtime crash||Test Case:|
|Related Tickets:||Differential Revisions:|
In HEAD, the following program sometimes deadlocks (about 1/10 of the time).
import Control.Concurrent import Control.Monad import GHC.Conc main = do mainTid <- myThreadId labelThread mainTid "main" forM_ [0..0] $ \i -> forkIO $ do subTid <- myThreadId labelThread subTid $ "sub " ++ show i forM_ [0..100000000] $ \j -> putStrLn $ "sub " ++ show i ++ ": " ++ show j yield setNumCapabilities 2
The problem seems to be that there is a race condition between setNumCapabilites and a Task returning from a foreign call. Specifically, a sequence of events like the following can happen:
- Task 0 makes a foreign call.
- Task 1 calls setNumCapabilities()
- The call on task 0 returns; it reads task->cap from the memory.
- Task 1 moves the Capabilities, invalidating all pointers to them.
- Task 0 takes over the invalidated Capability.
The attached patch adds an ASSERT to the RTS to demonstrate the problem (it does not fix the problem).
Change History (14)
Changed 18 months ago by akio
comment:1 Changed 18 months ago by parcs
comment:4 Changed 18 months ago by simonmar
- Owner set to simonmar
- Priority changed from normal to highest