Hi Artyom! Artyom Poptsov <poptsov.art...@gmail.com> skribis:
> please check if this branch will work without segfaults in Guix: > https://github.com/artyom-poptsov/guile-ssh/tree/wip-fix-segfaults-on-gc > > Key changes: > > - Channels are now protecting the parent session from GC'ing. > > - Every channel procedure now ensures that the parent session is > connected before calling any libssh procedures upon a channel > instance. The idea is that a channel cannot be created when a session > is disconnected and when channel is present and the session is closed, > it means that the session is disconnected and freed. Looks like the problem is still there, after all: --8<---------------cut here---------------start------------->8--- $ guix describe Generacio 154 Aug 29 2020 14:49:14 (nuna) guix 0ec6b8a repository URL: https://git.savannah.gnu.org/git/guix.git branch: master commit: 0ec6b8afd7e7a6c288fbf48c5779f2e0bdaffb55 $ guix copy --to=olimex coreutils-minimal sending 3 store items (86 MiB) to 'A20-OLinuXino.local'... Adres-eraro(nekropsio elŝutita) $ gdb $(type -P guile) core [...] Core was generated by `/gnu/store/0w76khfspfy8qmcpjya41chj3bgfcy0k-guile-3.0.4/bin/guile --no-auto-com'. Program terminated with signal SIGSEGV, Segmentation fault. warning: Unexpected size of section `.reg-xstate/25533' in core file. #0 0x00007f1ba90e4185 in deflate_fast () from /gnu/store/rykm237xkmq7rl1p0nwass01p090p88x-zlib-1.2.11/lib/libz.so.1 [Current thread is 1 (Thread 0x7f1baefb9b80 (LWP 25533))] (gdb) bt #0 0x00007f1ba90e4185 in deflate_fast () from /gnu/store/rykm237xkmq7rl1p0nwass01p090p88x-zlib-1.2.11/lib/libz.so.1 #1 0x00007f1ba90e653d in deflate () from /gnu/store/rykm237xkmq7rl1p0nwass01p090p88x-zlib-1.2.11/lib/libz.so.1 #2 0x00007f1ba89b1b4a in gzip_compress (session=session@entry=0x12a4b20, source=source@entry=0x12a5580, level=<optimized out>) at /tmp/guix-build-libssh-0.9.4.drv-0/source/src/gzip.c:91 #3 0x00007f1ba89b1e83 in compress_buffer (session=session@entry=0x12a4b20, buf=0x12a5580) at /tmp/guix-build-libssh-0.9.4.drv-0/source/src/gzip.c:112 #4 0x00007f1ba898eb5f in packet_send2 (session=session@entry=0x12a4b20) at /tmp/guix-build-libssh-0.9.4.drv-0/source/src/packet.c:1632 #5 0x00007f1ba898ec32 in ssh_packet_send (session=session@entry=0x12a4b20) at /tmp/guix-build-libssh-0.9.4.drv-0/source/src/packet.c:1810 #6 0x00007f1ba8978639 in channel_write_common (channel=0x12b0e90, data=0x7f1b9dba7020, len=65536, is_stderr=0) at /tmp/guix-build-libssh-0.9.4.drv-0/source/src/channels.c:1488 #7 0x00007f1ba89fce7a in write_to_channel_port () from /gnu/store/hw2wb78q8zxza1p1kdi8bffdbi1hb19n-guile-ssh-0.13.1/lib/libguile-ssh.so.13 #8 0x00007f1baf67eedc in scm_i_write_bytes (port=#<port #<port-type channel 7f1baaa1c6c0> 7f1ba7f25300>, src="#<vu8vector>" = {...}, start=0, count=65536) at ports.c:2865 #9 0x00007f1baf68686f in scm_put_bytevector (port=#<port #<port-type channel 7f1baaa1c6c0> 7f1ba7f25300>, bv="#<vu8vector>" = {...}, start=<optimized out>, count=<optimized out>) at r6rs-ports.c:676 [...] (gdb) info threads Id Target Id Frame * 1 Thread 0x7f1baefb9b80 (LWP 25533) 0x00007f1ba90e4185 in deflate_fast () from /gnu/store/rykm237xkmq7rl1p0nwass01p090p88x-zlib-1.2.11/lib/libz.so.1 2 Thread 0x7f1baec93700 (LWP 25534) warning: Unexpected size of section `.reg-xstate/25534' in core file. 0x00007f1baf56094c in futex_wait_cancelable (private=<optimized out>, expected=0, futex_word=0x7f1baf5b86e8 <mark_cv+40>) at ../sysdeps/nptl/futex-internal.h:183 3 Thread 0x7f1bac9d0700 (LWP 25537) warning: Unexpected size of section `.reg-xstate/25537' in core file. 0x00007f1ba90e479f in deflate_fast () from /gnu/store/rykm237xkmq7rl1p0nwass01p090p88x-zlib-1.2.11/lib/libz.so.1 4 Thread 0x7f1bae302700 (LWP 25535) warning: Unexpected size of section `.reg-xstate/25535' in core file. 0x00007f1baf56094c in futex_wait_cancelable (private=<optimized out>, expected=0, futex_word=0x7f1baf5b86e8 <mark_cv+40>) at ../sysdeps/nptl/futex-internal.h:183 5 Thread 0x7f1baa6f9700 (LWP 25538) warning: Unexpected size of section `.reg-xstate/25538' in core file. 0x00007f1baf5640a4 in __libc_read (fd=10, buf=buf@entry=0x7f1baa6f8660, nbytes=nbytes@entry=1) at ../sysdeps/unix/sysv/linux/read.c:26 6 Thread 0x7f1bad971700 (LWP 25536) warning: Unexpected size of section `.reg-xstate/25536' in core file. 0x00007f1baf56094c in futex_wait_cancelable (private=<optimized out>, expected=0, futex_word=0x7f1baf5b86e8 <mark_cv+40>) at ../sysdeps/nptl/futex-internal.h:183 (gdb) thread 3 [Switching to thread 3 (Thread 0x7f1bac9d0700 (LWP 25537))] #0 0x00007f1ba90e479f in deflate_fast () from /gnu/store/rykm237xkmq7rl1p0nwass01p090p88x-zlib-1.2.11/lib/libz.so.1 (gdb) bt #0 0x00007f1ba90e479f in deflate_fast () from /gnu/store/rykm237xkmq7rl1p0nwass01p090p88x-zlib-1.2.11/lib/libz.so.1 #1 0x00007f1ba90e653d in deflate () from /gnu/store/rykm237xkmq7rl1p0nwass01p090p88x-zlib-1.2.11/lib/libz.so.1 #2 0x00007f1ba89b1b4a in gzip_compress (session=session@entry=0x12a4b20, source=source@entry=0x12a5580, level=<optimized out>) at /tmp/guix-build-libssh-0.9.4.drv-0/source/src/gzip.c:91 #3 0x00007f1ba89b1e83 in compress_buffer (session=session@entry=0x12a4b20, buf=0x12a5580) at /tmp/guix-build-libssh-0.9.4.drv-0/source/src/gzip.c:112 #4 0x00007f1ba898eb5f in packet_send2 (session=session@entry=0x12a4b20) at /tmp/guix-build-libssh-0.9.4.drv-0/source/src/packet.c:1632 #5 0x00007f1ba898ec32 in ssh_packet_send (session=session@entry=0x12a4b20) at /tmp/guix-build-libssh-0.9.4.drv-0/source/src/packet.c:1810 #6 0x00007f1ba897a178 in ssh_channel_send_eof (channel=channel@entry=0x12b0930) at /tmp/guix-build-libssh-0.9.4.drv-0/source/src/channels.c:1250 #7 0x00007f1ba897a23b in ssh_channel_close (channel=0x12b0930) at /tmp/guix-build-libssh-0.9.4.drv-0/source/src/channels.c:1301 #8 0x00007f1ba89fcc36 in ptob_close () from /gnu/store/hw2wb78q8zxza1p1kdi8bffdbi1hb19n-guile-ssh-0.13.1/lib/libguile-ssh.so.13 #9 0x00007f1baf67c153 in release_port (port=#<port #<port-type channel 7f1baaa1c6c0> 7f1ba8e73400>) at ports.c:165 #10 0x00007f1baf67f19b in close_port (port=#<port #<port-type channel 7f1baaa1c6c0> 7f1ba8e73400>, explicit=<optimized out>) at ports.c:893 #11 0x00007f1baf63632a in scm_c_with_exception_handler (type=type@entry=#t, handler=handler@entry=0x7f1baf6ad7e0 <catch_post_unwind_handler>, handler_data=handler_data@entry=0x7f1bac9cf970, thunk=thunk@entry=0x7f1baf6ad920 <catch_body>, thunk_data=thunk_data@entry=0x7f1bac9cf970) at exceptions.c:170 #12 0x00007f1baf6adb1d in scm_c_catch (tag=tag@entry=#t, body=body@entry=0x7f1baf67f200 <do_close>, body_data=<optimized out>, handler=<optimized out>, handler_data=handler_data@entry=0x0, pre_unwind_handler=pre_unwind_handler@entry=0x0, pre_unwind_handler_data=0x0) at throw.c:168 #13 0x00007f1baf6adb3e in scm_internal_catch (tag=tag@entry=#t, body=body@entry=0x7f1baf67f200 <do_close>, body_data=<optimized out>, handler=<optimized out>, handler_data=handler_data@entry=0x0) at throw.c:177 #14 0x00007f1baf67ad84 in finalize_port (ptr=<optimized out>, data=<optimized out>) at ports.c:710 #15 0x00007f1baf58a6ef in GC_invoke_finalizers () from /gnu/store/iycnpxxrg8m9wf9w58d6zvp9sdby6m9d-libgc-7.6.12/lib/libgc.so.1 #16 0x00007f1baf63ee79 in scm_run_finalizers () at finalizers.c:399 #17 0x00007f1baf63eefd in finalization_thread_proc (unused=<optimized out>) at finalizers.c:234 --8<---------------cut here---------------end--------------->8--- So we have the finalization thread closing a channel of session 0x12a4b20 (which causes a write on the channel), and the main thread writing to a channel of that same session. This is exactly what I described at <https://issues.guix.gnu.org/26976#11>: AIUI, that means there’s one output compression buffer per session, and it’s not thread-safe (in Guile 2.2 finalizers are called from a separate thread.) I think the fix, in Guile-SSH, is to associate each libssh object (session, channel, etc.) with a mutex, and to protect all uses of the libssh object by that mutex. Artyom, WDYT? Do you think you could take a look into that? In the meantime, I’ll look for the origin of the channel port that’s not explicitly closed and see if we can work around it. Ludo’.
