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Subject: bug#52646: GC thread freeze
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From: Mathieu Othacehe <othacehe@HIDDEN>
Date: Sat, 18 Dec 2021 21:52:30 +0100
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Hello,
I experiment a strange behaviour with this Guile 3.0.7 process:
https://git.savannah.gnu.org/cgit/guix/guix-cuirass.git/tree/src/cuirass/scripts/remote-worker.scm.
The process is forking N processes that in turn start 4 threads. On
aarch64 machines specifically, some of those threads are freezing. Here
is what GDB is reporting:
--8<---------------cut here---------------start------------->8---
(gdb) attach 5660 ;frozen cuirass-remote-worker PID
(gdb) info thr
Id Target Id Frame
* 1 Thread 0xffffafd32e20 (LWP 5660) "yHg3r3fS" 0x0000ffffafb3fa80 in do_futex_wait.constprop () from /gnu/store/cb88z63hyg1icd2kkahiink2p291mhr2-glibc-2.31/lib/libpthread.so.0
2 Thread 0xffffa6c1c1d0 (LWP 5666) "ZMQbg/Reaper" 0x0000ffffaf7ec294 in epoll_pwait () from /gnu/store/cb88z63hyg1icd2kkahiink2p291mhr2-glibc-2.31/lib/libc.so.6
3 Thread 0xffffaf0071d0 (LWP 5667) "ZMQbg/IO/0" 0x0000ffffaf7ec294 in epoll_pwait () from /gnu/store/cb88z63hyg1icd2kkahiink2p291mhr2-glibc-2.31/lib/libc.so.6
4 Thread 0xffffa641b1d0 (LWP 5674) "yHg3r3fS" 0x0000ffffaf7b9d04 in clock_nanosleep@@GLIBC_2.17 () from /gnu/store/cb88z63hyg1icd2kkahiink2p291mhr2-glibc-2.31/lib/libc.so.6
(gdb) bt
#0 0x0000ffffafb3fa80 in do_futex_wait.constprop () from /gnu/store/cb88z63hyg1icd2kkahiink2p291mhr2-glibc-2.31/lib/libpthread.so.0
#1 0x0000ffffafb3fb78 in __new_sem_wait_slow.constprop.0 () from /gnu/store/cb88z63hyg1icd2kkahiink2p291mhr2-glibc-2.31/lib/libpthread.so.0
#2 0x0000ffffafb80318 in GC_stop_world () from /gnu/store/jsda4njqwjp4kb60fwa7n4mlfi1aanpq-libgc-7.6.12/lib/libgc.so.1
#3 0x0000ffffafb6c020 in GC_stopped_mark () from /gnu/store/jsda4njqwjp4kb60fwa7n4mlfi1aanpq-libgc-7.6.12/lib/libgc.so.1
#4 0x0000ffffafb6c8dc in GC_try_to_collect_inner () from /gnu/store/jsda4njqwjp4kb60fwa7n4mlfi1aanpq-libgc-7.6.12/lib/libgc.so.1
#5 0x0000ffffafb6d598 in GC_collect_or_expand () from /gnu/store/jsda4njqwjp4kb60fwa7n4mlfi1aanpq-libgc-7.6.12/lib/libgc.so.1
#6 0x0000ffffafb73b4c in GC_alloc_large () from /gnu/store/jsda4njqwjp4kb60fwa7n4mlfi1aanpq-libgc-7.6.12/lib/libgc.so.1
#7 0x0000ffffafb74038 in GC_generic_malloc () from /gnu/store/jsda4njqwjp4kb60fwa7n4mlfi1aanpq-libgc-7.6.12/lib/libgc.so.1
#8 0x0000ffffafb74298 in GC_malloc_kind_global () from /gnu/store/jsda4njqwjp4kb60fwa7n4mlfi1aanpq-libgc-7.6.12/lib/libgc.so.1
#9 0x0000ffffafc11fa8 in scm_make_bytevector () from /gnu/store/7g3nbnf2kf31jk696k0nyz9ck55b11a0-guile-3.0.7/lib/libguile-3.0.so.1
#10 0x0000ffffacacc418 in ?? ()
#11 0x0000ffffacc2ef2c in ?? ()
(gdb) thr 4
[Switching to thread 4 (Thread 0xffffa641b1d0 (LWP 5674))]
#0 0x0000ffffaf7b9d04 in clock_nanosleep@@GLIBC_2.17 () from /gnu/store/cb88z63hyg1icd2kkahiink2p291mhr2-glibc-2.31/lib/libc.so.6
(gdb) bt
#0 0x0000ffffaf7b9d04 in clock_nanosleep@@GLIBC_2.17 () from /gnu/store/cb88z63hyg1icd2kkahiink2p291mhr2-glibc-2.31/lib/libc.so.6
#1 0x0000ffffaf7bf55c in nanosleep () from /gnu/store/cb88z63hyg1icd2kkahiink2p291mhr2-glibc-2.31/lib/libc.so.6
#2 0x0000ffffafb7e844 in GC_lock () from /gnu/store/jsda4njqwjp4kb60fwa7n4mlfi1aanpq-libgc-7.6.12/lib/libgc.so.1
#3 0x0000ffffafb7ecdc in GC_do_blocking_inner () from /gnu/store/jsda4njqwjp4kb60fwa7n4mlfi1aanpq-libgc-7.6.12/lib/libgc.so.1
#4 0x0000ffffafb73998 in GC_with_callee_saves_pushed () from /gnu/store/jsda4njqwjp4kb60fwa7n4mlfi1aanpq-libgc-7.6.12/lib/libgc.so.1
#5 0x0000ffffafb79654 in GC_do_blocking () from /gnu/store/jsda4njqwjp4kb60fwa7n4mlfi1aanpq-libgc-7.6.12/lib/libgc.so.1
#6 0x0000ffffafc96d94 in scm_without_guile () from /gnu/store/7g3nbnf2kf31jk696k0nyz9ck55b11a0-guile-3.0.7/lib/libguile-3.0.so.1
#7 0x0000ffffafc97050 in scm_std_select () from /gnu/store/7g3nbnf2kf31jk696k0nyz9ck55b11a0-guile-3.0.7/lib/libguile-3.0.so.1
#8 0x0000ffffafc97b5c in scm_std_sleep () from /gnu/store/7g3nbnf2kf31jk696k0nyz9ck55b11a0-guile-3.0.7/lib/libguile-3.0.so.1
#9 0x0000ffffafc75918 in scm_sleep () from /gnu/store/7g3nbnf2kf31jk696k0nyz9ck55b11a0-guile-3.0.7/lib/libguile-3.0.so.1
#10 0x0000ffffa6c50d94 in ?? ()
#11 0x0000ffffacc2ee0c in ?? ()
--8<---------------cut here---------------end--------------->8---
The threads 1 and 4 do no respond anymore and are stuck, thread 1 on a
futex wait and thread 4 on a sleep, both in the GC library. For what
it's worth, I do not experiment this behaviour on x86 machines.
I tried to come up with a smaller reproducer without success, but I'll
keep trying.
Thanks,
Mathieu
Content-Disposition: inline Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-Mailer: MIME-tools 5.505 (Entity 5.505) Content-Type: text/plain; charset=utf-8 X-Loop: help-debbugs@HIDDEN From: help-debbugs@HIDDEN (GNU bug Tracking System) To: Mathieu Othacehe <othacehe@HIDDEN> Subject: bug#52646: Acknowledgement (GC thread freeze) Message-ID: <handler.52646.B.163986075719042.ack <at> debbugs.gnu.org> References: <878rwhbppt.fsf@HIDDEN> X-Gnu-PR-Message: ack 52646 X-Gnu-PR-Package: guile Reply-To: 52646 <at> debbugs.gnu.org Date: Sat, 18 Dec 2021 20:53:02 +0000 Thank you for filing a new bug report with debbugs.gnu.org. This is an automatically generated reply to let you know your message has been received. Your message is being forwarded to the package maintainers and other interested parties for their attention; they will reply in due course. Your message has been sent to the package maintainer(s): bug-guile@HIDDEN If you wish to submit further information on this problem, please send it to 52646 <at> debbugs.gnu.org. Please do not send mail to help-debbugs@HIDDEN unless you wish to report a problem with the Bug-tracking system. --=20 52646: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=3D52646 GNU Bug Tracking System Contact help-debbugs@HIDDEN with problems
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Subject: bug#52646: GC thread freeze
Resent-From: Ludovic =?UTF-8?Q?Court=C3=A8s?= <ludo@HIDDEN>
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From: Ludovic =?UTF-8?Q?Court=C3=A8s?= <ludo@HIDDEN>
References: <878rwhbppt.fsf@HIDDEN>
Date: Tue, 21 Dec 2021 11:16:36 +0100
In-Reply-To: <878rwhbppt.fsf@HIDDEN> (Mathieu Othacehe's message of "Sat, 18
Dec 2021 21:52:30 +0100")
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Hello!
Mathieu Othacehe <othacehe@HIDDEN> skribis:
> I experiment a strange behaviour with this Guile 3.0.7 process:
> https://git.savannah.gnu.org/cgit/guix/guix-cuirass.git/tree/src/cuirass/=
scripts/remote-worker.scm.
>
> The process is forking N processes that in turn start 4 threads.
This is happening in this order, right?
POSIX leaves unspecified the behavior of a child process forked from a
multi-threaded process; there could be deadlocks, etc. =E2=80=98primitive-=
fork=E2=80=99
prints a warning when called from a multi-threaded Guile process.
The solution is for multi-threaded Guile processes to not fork at all,
or to fork only via =E2=80=98open-pipe*=E2=80=99, =E2=80=98system*=E2=80=99=
, etc., which are =E2=80=9Cknown
good=E2=80=9D (they take care of post-fork handling in the child and call =
=E2=80=98exec=E2=80=99
before anything bad could happen.)
Thanks,
Ludo=E2=80=99.
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