Test failure in `LinearAlgebra/lapack`

[giordano]

Observed in Julia CI for i686-linux-gnu: https://buildkite.com/julialang/julia-master/builds/47172#01969e04-8a10-4791-ac12-153b4fc900e3/905-1708, this is also reproducible locally for me:

julia> Base.runtests("LinearAlgebra/lapack"; seed=0x4892b45f4810fc1b1f64f21e515d4024)
Running parallel tests with:
  getpid() = 4015
  nworkers() = 1
  nthreads(:interactive) = 1
  nthreads(:default) = 1
  Sys.CPU_THREADS = 2
  Sys.total_memory() = 3.872 GiB
  Sys.free_memory() = 3.139 GiB

Test             (Worker) | Time (s) | GC (s) | GC % | Alloc (MB) | RSS (MB)
LinearAlgebra/lapack  (1) |        started at 2025-05-05T19:02:25.247
LinearAlgebra/lapack  (1) |         failed at 2025-05-05T19:03:40.848
Test Failed at /home/mose/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.13/LinearAlgebra/test/lapack.jl:289
  Expression: b ≈ c
   Evaluated: Float32[159.31934, -64.649155, -2131.8872, 6787.0464, -12266.052, 295.2029, 2174.87, -1643.5519, -3781.9094, 2164.3667] ≈ Float32[159.25502, -64.62289, -2131.0276, 6784.31, -12261.106, 295.0839, 2173.9937, -1642.889, -3780.3843, 2
163.494]
Test Failed at /home/mose/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.13/LinearAlgebra/test/lapack.jl:316
  Expression: A \ b ≈ c
   Evaluated: Float32[-593.7424 -13.895346 … -225.10986 -702.97534; 243.55264 6.9179006 … 92.377785 287.7254; … ; 14076.482 338.5684 … 5353.0425 16684.324; -8053.3696 -192.93784 … -3062.0056 -9545.351] ≈ Float32[-593.98193 -13.901099 … -225.200
93 -703.25916; 243.65048 6.9202504 … 92.414986 287.84134; … ; 14082.161 338.70483 … 5355.2017 16691.057; -8056.6187 -193.0159 … -3063.2412 -9549.203]


Test Summary:            | Pass  Fail  Total     Time
  Overall                | 1181     2   1183  1m19.4s
    LinearAlgebra/lapack | 1181     2   1183  1m18.1s
    FAILURE

The global RNG seed was 0x4892b45f4810fc1b1f64f21e515d4024.

Error in testset LinearAlgebra/lapack:
Test Failed at /home/mose/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.13/LinearAlgebra/test/lapack.jl:289
  Expression: b ≈ c
   Evaluated: Float32[159.31934, -64.649155, -2131.8872, 6787.0464, -12266.052, 295.2029, 2174.87, -1643.5519, -3781.9094, 2164.3667] ≈ Float32[159.25502, -64.62289, -2131.0276, 6784.31, -12261.106, 295.0839, 2173.9937, -1642.889, -3780.3843, 2163.494]
Error in testset LinearAlgebra/lapack:
Test Failed at /home/mose/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.13/LinearAlgebra/test/lapack.jl:316
  Expression: A \ b ≈ c
   Evaluated: Float32[-593.7424 -13.895346 … -225.10986 -702.97534; 243.55264 6.9179006 … 92.377785 287.7254; … ; 14076.482 338.5684 … 5353.0425 16684.324; -8053.3696 -192.93784 … -3062.0056 -9545.351] ≈ Float32[-593.98193 -13.901099 … -225.20093 -703.25916; 243.65048 6.9202504 … 92.414986 287.84134; … ; 14082.161 338.70483 … 5355.2017 16691.057; -8056.6187 -193.0159 … -3063.2412 -9549.203]
ERROR: LoadError: Test run finished with errors
in expression starting at /home/mose/.julia/juliaup/julia-nightly/share/julia/test/runtests.jl:87
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 1.13.0-DEV.456
Commit 175ef3eb02c (2025-04-28 13:13 UTC)
Build Info:
  Official https://julialang.org release
Platform Info:
  OS: Linux (i686-linux-gnu)
  CPU: 4 × Intel(R) Core(TM) i5-4570 CPU @ 3.20GHz
  WORD_SIZE: 32
  LLVM: libLLVM-19.1.7 (ORCJIT, haswell)
  GC: Built with stock GC
Threads: 1 default, 1 interactive, 1 GC (on 4 virtual cores)

The offending tests are

LinearAlgebra.jl/test/lapack.jl

Lines 283 to 289 in 07725da

	du = rand(elty,9)
	d = rand(elty,10)
	dl = rand(elty,9)
	b = rand(elty,10)
	c = Tridiagonal(dl,d,du) \ b
	b = LAPACK.gtsv!(dl,d,du,b)
	@test b ≈ c

and

LinearAlgebra.jl/test/lapack.jl

Lines 299 to 316 in 07725da

	du = rand(elty,9)
	d = rand(elty,10)
	dl = rand(elty,9)
	b = rand(elty,10)
	y10 = Vector{BlasInt}(undef, 10)
	x9, x11 = Vector{elty}.(undef, (9, 11))
	@test_throws DimensionMismatch LAPACK.gttrf!(x11, d, du)
	@test_throws DimensionMismatch LAPACK.gttrf!(dl, d, x11)
	@test_throws DimensionMismatch LAPACK.gttrs!('N', x11, d, du, x9, y10, b)
	@test_throws DimensionMismatch LAPACK.gttrs!('N', dl, d, x11, x9, y10, b)
	@test_throws DimensionMismatch LAPACK.gttrs!('N', dl, d, du, x9, y10, x11)
	@test_throws ArgumentError LAPACK.gttrs!('X', dl, d, du, x9, y10, x11)
	A = lu(Tridiagonal(dl,d,du))
	b = rand(elty,10,5)
	c = copy(b)
	dl,d,du,du2,ipiv = LAPACK.gttrf!(dl,d,du)
	c = LAPACK.gttrs!('N',dl,d,du,du2,ipiv,c)
	@test A\b ≈ c

both for elty = Float32

[ViralBShah]

Can you locally reproduce on a 64-bit machine?

[giordano]

No, only 32-bit so far, but I could reproduce it exactly with the fixed seed.

[ViralBShah]

Where do you test it? Do you have a 32-bit linux machine, or can one run a whole 32-bit setup on 64-bit?

[giordano]

I got access to a 32-bit machine. I presume a VM/Docker would work as well.