Earlier this week the Linux/amd64 Harbormaster started failing somewhat reliably during validation. It seems the stage0 compiler (GHC 8.2.1) often fails with a segmentation fault. This seems to have started with ef26182e although I suspect this isn't causal. I was able to capture a core dump of the crashing stage0 compiler which implicates the allocator,

Reading symbols from /opt/ghc/8.2.1/lib/ghc-8.2.1/bin/ghc...(no debugging symbols found)...done.
[New LWP 25151]
[New LWP 25160]
[New LWP 25156]
[New LWP 25158]
[New LWP 25157]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `/opt/ghc/8.2.1/lib/ghc-8.2.1/bin/ghc -B/opt/ghc/8.2.1/lib/ghc-8.2.1 -hisuf hi -'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007f836aaa2c90 in ?? () from /opt/ghc/8.2.1/lib/ghc-8.2.1/bin/../rts/libHSrts_thr-ghc8.2.1.so
[Current thread is 1 (Thread 0x7f83711b5340 (LWP 25151))]
(gdb) bt
#0  0x00007f836aaa2c90 in ?? () from /opt/ghc/8.2.1/lib/ghc-8.2.1/bin/../rts/libHSrts_thr-ghc8.2.1.so
#1  0x00007f836aaa3211 in allocGroupOnNode () from /opt/ghc/8.2.1/lib/ghc-8.2.1/bin/../rts/libHSrts_thr-ghc8.2.1.so
#2  0x00007f836aa9dd41 in ?? () from /opt/ghc/8.2.1/lib/ghc-8.2.1/bin/../rts/libHSrts_thr-ghc8.2.1.so
#3  0x00007f836aa9deb9 in ?? () from /opt/ghc/8.2.1/lib/ghc-8.2.1/bin/../rts/libHSrts_thr-ghc8.2.1.so
#4  0x00007f836aa82a39 in ?? () from /opt/ghc/8.2.1/lib/ghc-8.2.1/bin/../rts/libHSrts_thr-ghc8.2.1.so
#5  0x00007f836aa7fc06 in ?? () from /opt/ghc/8.2.1/lib/ghc-8.2.1/bin/../rts/libHSrts_thr-ghc8.2.1.so
#6  0x00007f836aa9d461 in ?? () from /opt/ghc/8.2.1/lib/ghc-8.2.1/bin/../rts/libHSrts_thr-ghc8.2.1.so
#7  0x00007f836aaa423a in ?? () from /opt/ghc/8.2.1/lib/ghc-8.2.1/bin/../rts/libHSrts_thr-ghc8.2.1.so
#8  0x00007f836aaa4b3c in ?? () from /opt/ghc/8.2.1/lib/ghc-8.2.1/bin/../rts/libHSrts_thr-ghc8.2.1.so
#9  0x00007f836aa8bbc8 in ?? () from /opt/ghc/8.2.1/lib/ghc-8.2.1/bin/../rts/libHSrts_thr-ghc8.2.1.so
#10 0x00007f836aa8c912 in ?? () from /opt/ghc/8.2.1/lib/ghc-8.2.1/bin/../rts/libHSrts_thr-ghc8.2.1.so
#11 0x00007f836aa8da01 in scheduleWaitThread () from /opt/ghc/8.2.1/lib/ghc-8.2.1/bin/../rts/libHSrts_thr-ghc8.2.1.so
#12 0x00007f836aa99fae in hs_main () from /opt/ghc/8.2.1/lib/ghc-8.2.1/bin/../rts/libHSrts_thr-ghc8.2.1.so
#13 0x0000000000427038 in ?? ()
#14 0x00007f83694fd2b1 in __libc_start_main (main=0x426fd0, argc=119, argv=0x7fffcfee8078, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fffcfee8068) at ../csu/libc-start.c:291
#15 0x0000000000427069 in ?? ()