Hi! Mathieu Othacehe <m.othac...@gmail.com> skribis:
> While integrating (guix git) into Cuirass, I noticed unexpected > segfaults during "latest-repository-commit" evaluation. > > Segfaults can be narrowed to the following lines: > > (use-modules (git)) > (begin (libgit2-init!) > (let ((rep (repository-open "some-git-repo"))) > (remote-fetch (remote-lookup rep "origin"))) > (libgit2-shutdown)) > > > Note that, it's not 100% reproducible, but re-executing 4 or 5 times the > above snippet is often enough to observe the segfault. > > Here's the gdb backtrace I collected : > > #0 0x00007fffef7eb181 in git_mwindow_put_pack () from > /gnu/store/ilaffvq27kfy2la235hddkxcalj9r > #1 0x00007fffef7f2897 in pack_backend(float, long double,...)(...) () from > /gnu/store/ilaffvq2 > #2 0x00007fffef7eef72 in git_odb_free () from > /gnu/store/ilaffvq27kfy2la235hddkxcalj9r2i7-libg > #3 0x00007fffef8134ce in git_repository.cleanup () from > /gnu/store/ilaffvq27kfy2la235hddkxcalj > #4 0x00007fffef81351a in git_repository_free () from > /gnu/store/ilaffvq27kfy2la235hddkxcalj9r2 > #5 0x00007ffff7b01e37 in chained_finalizer () from > /gnu/store/5zx29y44nrqj0s8h3jlvlj82k8hj4dxs > #6 0x00007ffff785170f in GC_invoke_finalizers () from > /gnu/store/j4p7cnxb6byf1wra3yz6pk8av4g5m > #7 0x00007ffff7b02099 in scm_run_finalizers () from > /gnu/store/5zx29y44nrqj0s8h3jlvlj82k8hj4dx > #8 0x00007ffff7b020f5 in finalization_thread_proc () from > /gnu/store/5zx29y44nrqj0s8h3jlvlj82k > #9 0x00007ffff7af2cba in c_body () from > /gnu/store/5zx29y44nrqj0s8h3jlvlj82k8hj4dxs-guile-2.2. > #10 0x00007ffff7b680c9 in vm_debug_engine () from > /gnu/store/5zx29y44nrqj0s8h3jlvlj82k8hj4dxs-g > #11 0x00007ffff7b752aa in scm_call_n () from > /gnu/store/5zx29y44nrqj0s8h3jlvlj82k8hj4dxs-guile- > #12 0x00007ffff7b644e6 in catch () from > /gnu/store/5zx29y44nrqj0s8h3jlvlj82k8hj4dxs-guile-2.2.2 > #13 0x00007ffff7af32a0 in scm_i_with_continuation_barrier () from > /gnu/store/5zx29y44nrqj0s8h3j > #14 0x00007ffff7af3335 in scm_c_with_continuation_barrier () from > /gnu/store/5zx29y44nrqj0s8h3j > #15 0x00007ffff7b6310c in with_guile () from > /gnu/store/5zx29y44nrqj0s8h3jlvlj82k8hj4dxs-guile- > #16 0x00007ffff7858732 in GC_call_with_stack_base () from > /gnu/store/j4p7cnxb6byf1wra3yz6pk8av4 > #17 0x00007ffff7b63498 in scm_with_guile () from > /gnu/store/5zx29y44nrqj0s8h3jlvlj82k8hj4dxs-gu > #18 0x00007ffff7625454 in start_thread () from > /gnu/store/rmjlycdgiq8pfy5hfi42qhw3k7p6kdav-glib > #19 0x00007ffff5fed7bf in clone () from > /gnu/store/rmjlycdgiq8pfy5hfi42qhw3k7p6kdav-glibc-2.25/ > > I supposed that what happends is the following race-condition : > * (libgit2-shutdown) is called > * the finalizer %repository-free is called in an other thread. > * because shutdown has already been called the finalizer fails and > segfaults. Could be! I think using ‘libgit2-shutdown’ is risky because as you can see it can be tricky to implement it correctly. So my first recommendation would be to not try to use it. :-) Guile cannot really unload modules ATM anyway. To fix this, I think ‘libgit2-shutdown’ needs to call ‘scm_run_finalizers’ before calling ‘git_shutdown’, but I’m not sure if it’s enough. HTH, Ludo’.
