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Date: Thu, 29 Oct 2020 19:27:44 -0400
From: Rich Felker <dalias@...c.org>
To: Milan P. Stanić <mps@...anta.net>
Cc: musl@...ts.openwall.com
Subject: Re: [PATCH v2] MT fork
On Fri, Oct 30, 2020 at 12:00:07AM +0100, Milan P. Stanić wrote:
> On Thu, 2020-10-29 at 23:21, Szabolcs Nagy wrote:
> > * Milan P. Stanić <mps@...anta.net> [2020-10-29 21:55:41 +0100]:
> > > On Thu, 2020-10-29 at 17:13, Szabolcs Nagy wrote:
> > > > * Milan P. Stanić <mps@...anta.net> [2020-10-29 00:06:10 +0100]:
> > > > >
> > > > > Applied this patch on top of current musl master, build it on Alpine and
> > > > > installed.
> > > > >
> > > > > Tested by building ruby lang. Works fine.
> > > > > Also tested building zig lang, works fine.
> > > > > But crystal lang builds fine, but running it hangs. strace shows:
> > > > > -------------
> > > > > [pid 5573] futex(0x7efc50fba9e4, FUTEX_WAIT_PRIVATE, 2, NULL <unfinished ...>
> > > > > [pid 5568] futex(0x7efc5118f984, FUTEX_REQUEUE_PRIVATE, 0, 1, 0x7efc514b67a4) = 1
> > > > > [pid 5568] futex(0x7efc514b67a4, FUTEX_WAKE_PRIVATE, 1) = 1
> > > > > [pid 5571] <... futex resumed>) = 0
> > > > > [pid 5568] futex(0x7efc511099e4, FUTEX_WAIT_PRIVATE, 2, NULL <unfinished ...>
> > > > > [pid 5571] futex(0x7efc510409e4, FUTEX_WAIT_PRIVATE, 2, NULL
> > > > > -------------
> > > > > where it hangs.
> > > >
> > > > try to attach gdb to the process that hang and do
> > > >
> > > > thread apply all bt
> > > >
> > > > (make sure musl-dbg is installed)
> > >
> > > I cannot attach gdb for running process because my Alpine development
> > > boxes are lxc containers where CAP_SYS_PTRACE is not enabled afaik.
> >
> > there should be a way to config lxc to allow ptrace.
> >
> > > I installed musl-dbg and run program with 'gdb .build/crystal' and result is:
> > > ----------
> > > Reading symbols from .build/crystal...
> > > (gdb) run
> > > Starting program: /home/mps/aports/community/crystal/src/crystal-0.35.1/.build/crystal
> > >
> > > Program received signal SIGSEGV, Segmentation fault.
> >
> > hm segfault is not a hang..
> >
> > libgc tries to find stack bounds by registering a segfault handler
> > and walking stack pages until it triggers.
> >
> > gdb stops at signals, this one is harmless, you should just continue
> > until you see a hang, then interrupt and bt.
>
> I did continue now and stopped it when it hangs. Attached is gdb log
> produced by 'thread apply all bt'
Next time please don't gzip so it's readable and repliable. I've
expanded it out here though:
> Starting program: /home/mps/aports/community/crystal/src/crystal-0.35.1/.build/crystal
>
> Program received signal SIGSEGV, Segmentation fault.
> 0x00007ffff401c463 in GC_find_limit_with_bound () from /usr/lib/libgc.so.1
> Continuing.
> [New LWP 18867]
> [New LWP 18868]
> [New LWP 18869]
> [New LWP 18870]
> [New LWP 18871]
> [New LWP 18872]
> [New LWP 18873]
> [New LWP 18874]
> [New LWP 18875]
> [New LWP 18876]
> [New LWP 18877]
> [New LWP 18878]
> [New LWP 18879]
> [New LWP 18880]
> [New LWP 18881]
>
> Thread 1 "crystal" received signal SIGINT, Interrupt.
> __syscall_cp_c (nr=202, u=140737488349316, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> 61 ./arch/x86_64/syscall_arch.h: No such file or directory.
>
> Thread 16 (LWP 18881):
> #0 __syscall_cp_c (nr=202, u=140737280690660, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7ffff39f49e4) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7ffff39f49e4, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff40188b9 in GC_help_marker () from /usr/lib/libgc.so.1
> #6 0x00007ffff40206db in GC_mark_thread () from /usr/lib/libgc.so.1
> #7 0x00007ffff7fb9df7 in start (p=0x7ffff3a04aa0) at src/thread/pthread_create.c:196
> #8 0x00007ffff7fbbf93 in __clone () at src/thread/x86_64/clone.s:22
> Backtrace stopped: frame did not save the PC
>
> Thread 15 (LWP 18880):
> #0 __syscall_cp_c (nr=202, u=140737280965092, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7ffff3a379e4) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7ffff3a379e4, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff40188b9 in GC_help_marker () from /usr/lib/libgc.so.1
> #6 0x00007ffff40206db in GC_mark_thread () from /usr/lib/libgc.so.1
> #7 0x00007ffff7fb9df7 in start (p=0x7ffff3a47aa0) at src/thread/pthread_create.c:196
> #8 0x00007ffff7fbbf93 in __clone () at src/thread/x86_64/clone.s:22
> Backtrace stopped: frame did not save the PC
>
> Thread 14 (LWP 18879):
> #0 __syscall_cp_c (nr=202, u=140737281239524, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7ffff3a7a9e4) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7ffff3a7a9e4, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff40188b9 in GC_help_marker () from /usr/lib/libgc.so.1
> #6 0x00007ffff40206db in GC_mark_thread () from /usr/lib/libgc.so.1
> #7 0x00007ffff7fb9df7 in start (p=0x7ffff3a8aaa0) at src/thread/pthread_create.c:196
> #8 0x00007ffff7fbbf93 in __clone () at src/thread/x86_64/clone.s:22
> Backtrace stopped: frame did not save the PC
>
> Thread 13 (LWP 18878):
> #0 __syscall_cp_c (nr=202, u=140737281513956, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7ffff3abd9e4) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7ffff3abd9e4, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff40188b9 in GC_help_marker () from /usr/lib/libgc.so.1
> #6 0x00007ffff40206db in GC_mark_thread () from /usr/lib/libgc.so.1
> #7 0x00007ffff7fb9df7 in start (p=0x7ffff3acdaa0) at src/thread/pthread_create.c:196
> #8 0x00007ffff7fbbf93 in __clone () at src/thread/x86_64/clone.s:22
> Backtrace stopped: frame did not save the PC
>
> Thread 12 (LWP 18877):
> #0 __syscall_cp_c (nr=202, u=140737281788388, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7ffff3b009e4) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7ffff3b009e4, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff40188b9 in GC_help_marker () from /usr/lib/libgc.so.1
> #6 0x00007ffff40206db in GC_mark_thread () from /usr/lib/libgc.so.1
> #7 0x00007ffff7fb9df7 in start (p=0x7ffff3b10aa0) at src/thread/pthread_create.c:196
> #8 0x00007ffff7fbbf93 in __clone () at src/thread/x86_64/clone.s:22
> Backtrace stopped: frame did not save the PC
>
> Thread 11 (LWP 18876):
> #0 __syscall_cp_c (nr=202, u=140737282062820, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7ffff3b439e4) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7ffff3b439e4, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff40188b9 in GC_help_marker () from /usr/lib/libgc.so.1
> #6 0x00007ffff40206db in GC_mark_thread () from /usr/lib/libgc.so.1
> #7 0x00007ffff7fb9df7 in start (p=0x7ffff3b53aa0) at src/thread/pthread_create.c:196
> #8 0x00007ffff7fbbf93 in __clone () at src/thread/x86_64/clone.s:22
> Backtrace stopped: frame did not save the PC
>
> Thread 10 (LWP 18875):
> #0 __syscall_cp_c (nr=202, u=140737282337252, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7ffff3b869e4) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7ffff3b869e4, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff40188b9 in GC_help_marker () from /usr/lib/libgc.so.1
> #6 0x00007ffff40206db in GC_mark_thread () from /usr/lib/libgc.so.1
> #7 0x00007ffff7fb9df7 in start (p=0x7ffff3b96aa0) at src/thread/pthread_create.c:196
> #8 0x00007ffff7fbbf93 in __clone () at src/thread/x86_64/clone.s:22
> Backtrace stopped: frame did not save the PC
>
> Thread 9 (LWP 18874):
> #0 __syscall_cp_c (nr=202, u=140737282611684, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7ffff3bc99e4) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7ffff3bc99e4, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff40188b9 in GC_help_marker () from /usr/lib/libgc.so.1
> #6 0x00007ffff40206db in GC_mark_thread () from /usr/lib/libgc.so.1
> #7 0x00007ffff7fb9df7 in start (p=0x7ffff3bd9aa0) at src/thread/pthread_create.c:196
> #8 0x00007ffff7fbbf93 in __clone () at src/thread/x86_64/clone.s:22
> Backtrace stopped: frame did not save the PC
>
> Thread 8 (LWP 18873):
> #0 __syscall_cp_c (nr=202, u=140737282886020, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7ffff3c0c984) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7ffff3c0c984, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff40186ca in GC_mark_local () from /usr/lib/libgc.so.1
> #6 0x00007ffff40188f4 in GC_help_marker () from /usr/lib/libgc.so.1
> #7 0x00007ffff40206db in GC_mark_thread () from /usr/lib/libgc.so.1
> #8 0x00007ffff7fb9df7 in start (p=0x7ffff3c1caa0) at src/thread/pthread_create.c:196
> #9 0x00007ffff7fbbf93 in __clone () at src/thread/x86_64/clone.s:22
> Backtrace stopped: frame did not save the PC
>
> Thread 7 (LWP 18872):
> #0 __syscall_cp_c (nr=202, u=140737283160548, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7ffff3c4f9e4) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7ffff3c4f9e4, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff40188b9 in GC_help_marker () from /usr/lib/libgc.so.1
> #6 0x00007ffff40206db in GC_mark_thread () from /usr/lib/libgc.so.1
> #7 0x00007ffff7fb9df7 in start (p=0x7ffff3c5faa0) at src/thread/pthread_create.c:196
> #8 0x00007ffff7fbbf93 in __clone () at src/thread/x86_64/clone.s:22
> Backtrace stopped: frame did not save the PC
>
> Thread 6 (LWP 18871):
> #0 __syscall_cp_c (nr=202, u=140737283434980, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7ffff3c929e4) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7ffff3c929e4, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff40188b9 in GC_help_marker () from /usr/lib/libgc.so.1
> #6 0x00007ffff40206db in GC_mark_thread () from /usr/lib/libgc.so.1
> #7 0x00007ffff7fb9df7 in start (p=0x7ffff3ca2aa0) at src/thread/pthread_create.c:196
> #8 0x00007ffff7fbbf93 in __clone () at src/thread/x86_64/clone.s:22
> Backtrace stopped: frame did not save the PC
>
> Thread 5 (LWP 18870):
> #0 __syscall_cp_c (nr=202, u=140737283709412, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7ffff3cd59e4) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7ffff3cd59e4, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff40188b9 in GC_help_marker () from /usr/lib/libgc.so.1
> #6 0x00007ffff40206db in GC_mark_thread () from /usr/lib/libgc.so.1
> #7 0x00007ffff7fb9df7 in start (p=0x7ffff3ce5aa0) at src/thread/pthread_create.c:196
> #8 0x00007ffff7fbbf93 in __clone () at src/thread/x86_64/clone.s:22
> Backtrace stopped: frame did not save the PC
>
> Thread 4 (LWP 18869):
> #0 __syscall_cp_c (nr=202, u=140737283983844, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7ffff3d189e4) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7ffff3d189e4, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff40188b9 in GC_help_marker () from /usr/lib/libgc.so.1
> #6 0x00007ffff40206db in GC_mark_thread () from /usr/lib/libgc.so.1
> #7 0x00007ffff7fb9df7 in start (p=0x7ffff3d28aa0) at src/thread/pthread_create.c:196
> #8 0x00007ffff7fbbf93 in __clone () at src/thread/x86_64/clone.s:22
> Backtrace stopped: frame did not save the PC
>
> Thread 3 (LWP 18868):
> #0 __syscall_cp_c (nr=202, u=140737284258276, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7ffff3d5b9e4) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7ffff3d5b9e4, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff40188b9 in GC_help_marker () from /usr/lib/libgc.so.1
> #6 0x00007ffff40206db in GC_mark_thread () from /usr/lib/libgc.so.1
> #7 0x00007ffff7fb9df7 in start (p=0x7ffff3d6baa0) at src/thread/pthread_create.c:196
> #8 0x00007ffff7fbbf93 in __clone () at src/thread/x86_64/clone.s:22
> Backtrace stopped: frame did not save the PC
>
> Thread 2 (LWP 18867):
> #0 __syscall_cp_c (nr=202, u=140737284532708, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7ffff3d9e9e4) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7ffff3d9e9e4, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff40188b9 in GC_help_marker () from /usr/lib/libgc.so.1
> #6 0x00007ffff40206db in GC_mark_thread () from /usr/lib/libgc.so.1
> #7 0x00007ffff7fb9df7 in start (p=0x7ffff3daeaa0) at src/thread/pthread_create.c:196
> #8 0x00007ffff7fbbf93 in __clone () at src/thread/x86_64/clone.s:22
> Backtrace stopped: frame did not save the PC
>
> Thread 1 (LWP 18859):
> #0 __syscall_cp_c (nr=202, u=140737488349316, v=128, w=2, x=0, y=0, z=0) at ./arch/x86_64/syscall_arch.h:61
> #1 0x00007ffff7fb8937 in __futex4_cp (to=0x0, val=2, op=128, addr=0x7fffffffe884) at src/thread/__timedwait.c:52
> #2 __timedwait_cp (addr=addr@...ry=0x7fffffffe884, val=val@...ry=2, clk=clk@...ry=0, at=at@...ry=0x0, priv=128, priv@...ry=1) at src/thread/__timedwait.c:52
> #3 0x00007ffff7fb9740 in __pthread_cond_timedwait (c=0x7ffff403fba0, m=0x7ffff403f7a0, ts=0x0) at src/thread/pthread_cond_timedwait.c:100
> #4 0x00007ffff40206fd in GC_wait_marker () from /usr/lib/libgc.so.1
> #5 0x00007ffff4018852 in GC_do_parallel_mark () from /usr/lib/libgc.so.1
> #6 0x00007ffff401937c in GC_mark_some () from /usr/lib/libgc.so.1
> #7 0x00007ffff4010e5a in GC_stopped_mark () from /usr/lib/libgc.so.1
> #8 0x00007ffff40114d4 in GC_try_to_collect_inner () from /usr/lib/libgc.so.1
> #9 0x00007ffff401b47f in GC_init () from /usr/lib/libgc.so.1
> #10 0x00005555555668d8 in init () at /home/mps/aports/community/crystal/src/crystal-0.35.1/src/gc/boehm.cr:127
> #11 main () at /home/mps/aports/community/crystal/src/crystal-0.35.1/src/crystal/main.cr:35
> #12 main () at /home/mps/aports/community/crystal/src/crystal-0.35.1/src/crystal/main.cr:114
OK, I'm looking at Boehm-GC's GC_wait_marker and this function is
utterly bogus. It's using a condition variable without a predicate,
and the corresponding broadcast operation runs without the lock held,
so it's inherently subject both to spurious wakes and missed wakes.
Here's the source:
https://github.com/ivmai/bdwgc/blob/57b97be07c514fcc4b608b13768fd2bf637a5899/pthread_support.c#L2374
This code is only used if built with PARALLEL_MARK defined, and
obviously does not and cannot work, so I think the best solution is
just figuring out how to turn off PARALLEL_MARK.
Do you have reason to believe the problem here has anything to do with
the MT-fork patch? Was it maybe just hanging somewhere earlier without
the patch, and now hanging on an independent bug?
Rich
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