Issue 1:
We haven't been running the testsuite on PPC64le so far, so when I started doing so on the next iteration of the buildbots, I noticed that we don't actually make it through the sparse/sparse tests:

julia> Base.runtests("sparse/sparse")
Test (Worker) | Time (s) | GC (s) | GC % | Alloc (MB) | RSS (MB)

signal (11): Segmentation fault
while loading /home/juliabuild/buildbot/slave/package_tarballppc64le/build/usr/share/julia/test/sparse/sparse.jl, in expression starting on line 1466
umfzl_create_element at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/usr/bin/../lib/libumfpack.so (unknown line)
umfzl_kernel at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/usr/bin/../lib/libumfpack.so (unknown line)
umfpack_zl_numeric at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/usr/bin/../lib/libumfpack.so (unknown line)
umfpack_numeric! at ./sparse/umfpack.jl:240
lufact at ./sparse/umfpack.jl:148
factorize at ./sparse/linalg.jl:897
normestinv at ./sparse/linalg.jl:552
cond at ./sparse/linalg.jl:534
macro expansion; at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/usr/share/julia/test/sparse/sparse.jl:1474 [inlined]
macro expansion; at ./test.jl:842 [inlined]
anonymous at ./<missing> (unknown line)
jl_call_method_internal at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/julia_internal.h:248 [inlined]
jl_toplevel_eval_flex at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/toplevel.c:652
jl_parse_eval_all at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/ast.c:756
jl_load at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/toplevel.c:679
jl_load_ at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/toplevel.c:686
include_from_node1 at ./loading.jl:532
unknown function (ip: 0x3fff71f325f3)
jl_call_method_internal at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/julia_internal.h:248 [inlined]
jl_apply_generic at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/gf.c:2214
include at ./sysimg.jl:14
macro expansion; at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/usr/share/julia/test/testdefs.jl:13 [inlined]
macro expansion; at ./test.jl:842 [inlined]
macro expansion; at ./util.jl:288 [inlined]
macro expansion; at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/usr/share/julia/test/testdefs.jl:0 [inlined]
anonymous at ./<missing> (unknown line)
jl_call_method_internal at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/julia_internal.h:248 [inlined]
jl_toplevel_eval_flex at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/toplevel.c:652
jl_toplevel_eval_in at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/builtins.c:614
eval at ./boot.jl:238
unknown function (ip: 0x3fff71f0df97)
jl_call_method_internal at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/julia_internal.h:248 [inlined]
jl_apply_generic at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/gf.c:2214
runtests at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/usr/share/julia/test/testdefs.jl:16
#483 at ./multi.jl:1053
run_work_thunk at ./multi.jl:1024
unknown function (ip: 0x3ffd48d146d3)
jl_call_method_internal at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/julia_internal.h:248 [inlined]
jl_apply_generic at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/gf.c:2214
#remotecall_fetch#488 at ./multi.jl:1078
jl_call_method_internal at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/julia_internal.h:248 [inlined]
jl_apply_generic at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/gf.c:2214
jl_apply at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/julia.h:1413 [inlined]
jl_f__apply at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/builtins.c:556
remotecall_fetch at ./multi.jl:1078
jl_call_method_internal at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/julia_internal.h:248 [inlined]
jl_apply_generic at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/gf.c:2214
jl_apply at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/julia.h:1413 [inlined]
jl_f__apply at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/builtins.c:556
#remotecall_fetch#492 at ./multi.jl:1106
jl_call_method_internal at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/julia_internal.h:248 [inlined]
jl_apply_generic at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/gf.c:2214
jl_apply at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/julia.h:1413 [inlined]
jl_f__apply at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/builtins.c:556
remotecall_fetch at ./multi.jl:1106
jl_call_method_internal at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/julia_internal.h:248 [inlined]
jl_apply_generic at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/gf.c:2214
macro expansion at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/usr/share/julia/test/runtests.jl:65 [inlined]
#38 at ./task.jl:332
unknown function (ip: 0x3ffd48d10e17)
jl_call_method_internal at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/julia_internal.h:248 [inlined]
jl_apply_generic at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/gf.c:2214
jl_apply at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/julia.h:1413 [inlined]
start_task at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/task.c:261
jl_set_base_ctx at /home/juliabuild/buildbot/slave/package_tarballppc64le/build/src/task.c:282
Allocations: 48258430 (Pool: 48252559; Big: 5871); GC: 260
ERROR: A test has failed. Please submit a bug report (https://github.com/JuliaLang/julia/issues)
including error messages above and the output of versioninfo():
Julia Version 0.6.0-dev.2143
Commit f4cbc40 (2017-01-19 01:42 UTC)
Platform Info:
OS: Linux (powerpc64le-unknown-linux-gnu)
CPU: unknown
WORD_SIZE: 64
BLAS: libopenblas (NO_AFFINITY POWER8)
LAPACK: libopenblas
LIBM: libopenlibm
LLVM: libLLVM-3.9.1 (ORCJIT, pwr8)

Looks like it's pointing to this block of code as the culprit, but it doesn't trigger when I just run that piece of code manually. Reporting here in case anyone else wants to take a shot at this.

Issue 2:
This appears to be a bug in rand(), that we have seen pop up in our CI a few times over the last couple months:

ERROR: LoadError: TaskFailedException:
InexactError: check_top_bit(UInt64, -64)
Stacktrace:
[1] throw_inexacterror(::Symbol, ::Type{UInt64}, ::Int64) at ./boot.jl:558
[2] check_top_bit at ./boot.jl:572 [inlined]
[3] toUInt64 at ./boot.jl:683 [inlined]
[4] UInt64 at ./boot.jl:713 [inlined]
[5] convert at ./number.jl:7 [inlined]
[6] cconvert at ./essentials.jl:388 [inlined]
[7] unsafe_copyto! at ./array.jl:245 [inlined]
[8] _rand_max383!(::Random.MersenneTwister, ::Random.UnsafeView{Float64}, ::Random.CloseOpen12{Float64}) at /build/source/usr/share/julia/stdlib/v1.5/Random/src/RNGs.jl:452
[9] rand!(::Random.MersenneTwister, ::Random.UnsafeView{Float64}, ::Random.SamplerTrivial{Random.CloseOpen12{Float64},Float64}) at /build/source/usr/share/julia/stdlib/v1.5/Random/src/RNGs.jl:486
[10] rand! at /build/source/usr/share/julia/stdlib/v1.5/Random/src/Random.jl:266 [inlined]
[11] rand!(::Random.MersenneTwister, ::Random.UnsafeView{UInt128}, ::Random.SamplerType{UInt128}) at /build/source/usr/share/julia/stdlib/v1.5/Random/src/RNGs.jl:567
[12] rand! at /build/source/usr/share/julia/stdlib/v1.5/Random/src/RNGs.jl:590 [inlined]
[13] rand! at /build/source/usr/share/julia/stdlib/v1.5/Random/src/Random.jl:267 [inlined] (repeats 2 times)
[14] mt_setfull! at /build/source/usr/share/julia/stdlib/v1.5/Random/src/RNGs.jl:215 [inlined]
[15] reserve1 at /build/source/usr/share/julia/stdlib/v1.5/Random/src/RNGs.jl:222 [inlined]
[16] mt_pop! at /build/source/usr/share/julia/stdlib/v1.5/Random/src/RNGs.jl:227 [inlined]
[17] rand at /build/source/usr/share/julia/stdlib/v1.5/Random/src/RNGs.jl:392 [inlined]
[18] rand at /build/source/usr/share/julia/stdlib/v1.5/Random/src/Random.jl:256 [inlined]
[19] rand(::Random.MersenneTwister, ::Random.SamplerRangeNDL{UInt64,Int64}) at /build/source/usr/share/julia/stdlib/v1.5/Random/src/generation.jl:326
[20] rand at /build/source/usr/share/julia/stdlib/v1.5/Random/src/Random.jl:253 [inlined]
[21] sample at /nix/store/k1nz08681liijdmz9y47x8b5qzz8yvyi-delve-binary-linux/delve/.julia/packages/StatsBase/EA8Mh/src/sampling.jl:388 [inlined]

The build that seems to exhibit this failure is calling rand() repeatedly across thousands of tasks in a process running with JULIA_NUM_THREADS=8.

This is on julia 1.5.3, on a (nix) source-build, on linux.

Thanks!