#10296: Segfaults when using dynamic wrappers and concurrency -------------------------------------+------------------------------------- Reporter: bitonic | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- I had a largish program that sometimes segfaulted, the segfault seemingly coming from the code that gets a C pointer from an Haskell function. After much sweat I've managed to produce a self-contained program that exhibits the same behavior: {{{ bitonic@clay /tmp/ptr-crash % uname -a Linux clay 3.13.0-48-generic #80-Ubuntu SMP Thu Mar 12 11:16:15 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux bitonic@clay /tmp/ptr-crash % cabal configure --disable-library-profiling -w ghc-7.11.20150411 Resolving dependencies... Configuring ptr-crash-0... bitonic@clay /tmp/ptr-crash % cabal build Building ptr-crash-0... Preprocessing executable 'ptr-crash' for ptr-crash-0... [1 of 1] Compiling Main ( Main.hs, dist/build/ptr-crash/ptr- crash-tmp/Main.o ) Linking dist/build/ptr-crash/ptr-crash ... bitonic@clay /tmp/ptr-crash % strace -f -r -o strace-out ./dist/build/ptr- crash/ptr-crash +RTS -N2 -RTS [1] 26612 segmentation fault (core dumped) strace -f -r -o strace-out ./dist/build/ptr-crash/ptr-crash +RTS -N2 -RTS }}} I'm running GHC HEAD on a Linux 64bit machine. In the larger program, I'm pretty sure the segfaults happened on GHC 7.8.4 too, but currently I can reproduce it only on 7.10 and later. More details (thanks to Sergei Trofimovich on #ghc for helping me in investigating this): * The segfault only happens when using `-N2` or more. * Curiously, the segfault seems to happen much more often when compiling the program with `-g`. * `strace`ing the program when segfaulting shows that all the threads crash together right after some calls to `mremap`. I've attached the end of the output of `strace`. * `gdb`ing the program and breaking on `mremap` shows that all the calls to `mremap` originate from `getStablePtr`. I've attached a run of `gdb` that shows this pattern. Sergei had a hunch that this had to do with thread-unsafe calls to `mremap`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10296 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler