Failure in multi-threaded application with GoogleCloud.jl and HTTP.jl

[nlw0]

I'm working with GoogleCloud.jl, which depends on MbedTLS.jl. Sometimes I've been getting errors like this:

┌ Error: Exception in task
│   exception =
│    MbedTLS error code -17280: RSA - The PKCS#1 verification failed
│    Stacktrace:
│      [1] mbed_err(ret::Int32)

┌ Error: Exception in task
│   exception =
│    MbedTLS error code -17162: RSA - The private key operation failed : BIGNUM - The input arguments are negative or result in illegal output
│    Stacktrace:
│      [1] mbed_err(ret::Int32)
│        @ MbedTLS ~/.julia/packages/MbedTLS/4YY6E/src/error.jl:17
│      [2] macro expansion
│        @ ~/.julia/packages/MbedTLS/4YY6E/src/error.jl:4 [inlined]
│      [3] sign!
│        @ ~/.julia/packages/MbedTLS/4YY6E/src/pk.jl:90 [inlined]
│      [4] sign(ctx::MbedTLS.PKContext, hash_alg::MbedTLS.MDKind, hash::Vector{UInt8}, rng::Random.MersenneTwister)
│        @ MbedTLS ~/.julia/packages/MbedTLS/4YY6E/src/pk.jl:100
│      [5] SHA256withRSA
│        @ ~/src/vdm-service/GoogleCloud.jl/src/session.jl:26 [inlined]
│      [6] JWS(credentials::GoogleCloud.credentials.JSONCredentials, claimset::GoogleCloud.session.JWTClaimSet, header::GoogleCloud.session.JWTHeader)
│        @ GoogleCloud.session ~/src/vdm-service/GoogleCloud.jl/src/session.jl:140
│      [7] JWS
│        @ ~/src/vdm-service/GoogleCloud.jl/src/session.jl:139 [inlined]
│      [8] token(credentials::GoogleCloud.credentials.JSONCredentials, scopes::Vector{String})
│        @ GoogleCloud.session ~/src/vdm-service/GoogleCloud.jl/src/session.jl:148
│      [9] authorize(session::GoogleCloud.session.GoogleSession{GoogleCloud.credentials.JSONCredentials}; cache::Bool)
│        @ GoogleCloud.session ~/src/vdm-service/GoogleCloud.jl/src/session.jl:181
│     [10] authorize
│        @ ~/src/vdm-service/GoogleCloud.jl/src/session.jl:177 [inlined]
│     [11] execute(session::GoogleCloud.session.GoogleSession{GoogleCloud.credentials.JSONCredentials}, resource::GoogleCloud.api.APIResource, method::GoogleCloud.api.APIMethod, path_args::String; data::Vector{UInt8}, gzip::Bool, content_type::String, debug::Bool, raw::Bool, max_backoff::Dates.Second, max_attempts::Int64, params::Base.Pairs{Symbol, String, Tuple{Symbol}, NamedTuple{(:fields,), Tuple{String}}})
│        @ GoogleCloud.api ~/src/vdm-service/GoogleCloud.jl/src/api/api.jl:241
│     [12] (::GoogleCloud.api.APIRoot)(resource_name::Symbol, method_name::Symbol, args::String; kwargs::Base.Pairs{Symbol, Any, Tuple{Symbol, Symbol, Symbol}, NamedTuple{(:session, :fields, :debug), Tuple{GoogleCloud.session.GoogleSession{GoogleCloud.credentials.JSONCredentials}, String, Bool}}})
│        @ GoogleCloud.api ~/src/vdm-service/GoogleCloud.jl/src/api/api.jl:218
│     [13] connect!(store::GoogleCloud.collection.KeyStore{String, CuboidService.PointCloud}; location::String, empty::Bool, debug::Bool)
│        @ GoogleCloud.collection ~/src/vdm-service/GoogleCloud.jl/src/collection.jl:79
│     [14] GoogleCloud.collection.KeyStore{String, CuboidService.PointCloud}(bucket_name::String; session::GoogleCloud.session.GoogleSession{GoogleCloud.credentials.JSONCredentials}, location::String, empty::Bool, gzip::Bool, key_format::Symbol, val_format::Symbol, debug::Bool)
│        @ GoogleCloud.collection ~/src/vdm-service/GoogleCloud.jl/src/collection.jl:73

I'm thinking it might be due to thread conflicts. Is MbedTLS thread-safe? Any recommendations how I might debug this? Or perhaps this might need to be fixed within GoogleCloud.jl?

[quinnj]

Hmmmm.....looking through the involved code, it doesn't seem like there's anything obviously non-multithread-safe. Though I also can't find documentation that the call to mbedtls_pk_sign in the mbedtls C library is threadsafe. So possibly? It's possible that putting a lock in JSONCredentials around the private_key field might help; probably worth a shot.

HTTP.jl itself has had threadsafety issues in the 0.9 releases; the 1.0 release just came out that should resolve those, but I don't think GoogleCloud has updated for compatibility there yet (hopefully not too hard). But it doesn't look like this particular code path deals w/ HTTP.jl at all.

[nlw0]

Thanks for taking a look, @quinnj . I'm looking at GoogleCloud.jl/src/session.jl:26, and considering I have a shared global GoogleSession object, I'm wondering if this can cause a problem. One attempt at using locks hasn't solved it, but maybe I need to change the approach. I'm not familiar with how TLS works, but maybe there's a random generator state that cannot be shared across threads? I'm not sure what parts of my code should go into a mutex in that case, or if I should have separate GoogleSession object. I'm not sure that'd be even even possible, so it's confusing.

And that might not be the whole story, because sometimes I get a segfault or a double-free error, the kind of thing we would really call non-thread-safe. But that's more difficult to reproduce.

[nlw0]

GoogleCloud.jl methods can take an optional session argument, I believe using that with new sessions every thread has solved my problem. Thanks for the help!

[nlw0]

I thought the problem was gone after I started using separate session objects, but I've actually got the issue again. I'll try to come up with a minimal example...

[nlw0]

I have created a short script that reproduces the issue, here's how it goes:

using GoogleCloud
using MD5, Base64

goocredentials = JSONCredentials("mycreds-123443211234.json")
mybucket = "mybucket-1234"
mypaths = ["..." for n in 1:23]  ## 54 different files

mydata = map(mypaths) do path
    # begin
    # @async begin
    Threads.@spawn begin
        goosession = GoogleSession(goocredentials, ["devstorage.full_control"])
        data = storage(:Object, :get, mybucket, path, session=goosession)
    end
end

allbytes = reduce(vcat, fetch.(mydata))
@show base64encode(md5(allbytes))

Running with julia -t1 it works, and using either begin or @async begin it works. With Threads.@spawn it reliably breaks with julia -t2.

I'm sorry I can't share my data, I can try to set up something public if it helps.

It's not always the same error. One of the errors I get is what I'm seeing most often in my real code, nested task error: MbedTLS error code -17280: RSA - The PKCS#1 verification failed. Other than that, I get things that look like memory allocation errors such as free(): corrupted unsorted chunks, signal (11): Segmentation fault and malloc(): smallbin double linked list corrupted

This looks to me like something in MbedTLS not being thread-safe, even with separate GoogleSession objects.

[nlw0]

I don't know why I didn't see this before, but there really seem to be known issues with MbedTLS in multiple threads:
Mbed-TLS/mbedtls#3391
Mbed-TLS/mbedtls#3263

I created a PR on GoogleCloud.jl, but should anything be done in this library? At least a warning in the documentation, perhaps?

[nlw0]

JuliaCloud/GoogleCloud.jl#48

[quinnj]

Should have been fixed via #245