Try to fix deadlock in code loading (#28416)

If a precompiled package's init function tries to itself require that
package (e.g. by importing a symbol from a submodule of that package),
we would run into a deadlock. Fix that by delaying the running of
initializers until after we've had a chance to register any root module.

Fixes #26028

base/loading.jl

@@ -611,7 +611,8 @@ end
 # or an Exception that describes why it couldn't be loaded
 # and it reconnects the Base.Docs.META
 function _include_from_serialized(path::String, depmods::Vector{Any})
-    restored = ccall(:jl_restore_incremental, Any, (Cstring, Any), path, depmods)
+    sv = ccall(:jl_restore_incremental, Any, (Cstring, Any), path, depmods)
+    restored = sv[1]
     if !isa(restored, Exception)
         for M in restored::Vector{Any}
             M = M::Module
@@ -623,6 +624,7 @@ function _include_from_serialized(path::String, depmods::Vector{Any})
             end
         end
     end
+    isassigned(sv, 2) && ccall(:jl_init_restored_modules, Cvoid, (Any,), sv[2])
     return restored
 end
 

src/dump.c

@@ -2402,7 +2402,7 @@ static jl_array_t *jl_finalize_deserializer(jl_serializer_state *s, arraylist_t
     return init_order;
 }
 
-static void jl_init_restored_modules(jl_array_t *init_order)
+JL_DLLEXPORT void jl_init_restored_modules(jl_array_t *init_order)
 {
     if (!init_order)
         return;
@@ -3118,10 +3118,10 @@ static jl_value_t *_jl_restore_incremental(ios_t *f, jl_array_t *mod_array)
         arraylist_free(tracee_list);
         free(tracee_list);
     }
-    jl_init_restored_modules(init_order);
+    jl_value_t *ret = (jl_value_t*)jl_svec(2, restored, init_order);
     JL_GC_POP();
 
-    return (jl_value_t*)restored;
+    return (jl_value_t*)ret;
 }
 
 JL_DLLEXPORT jl_value_t *jl_restore_incremental_from_buf(const char *buf, size_t sz, jl_array_t *mod_array)

test/precompile.jl

@@ -700,4 +700,41 @@ let
     end
 end
 
+let
+    load_path = mktempdir()
+    load_cache_path = mktempdir()
+    try
+        write(joinpath(load_path, "Foo26028.jl"),
+            """
+            module Foo26028
+
+            module Bar26028
+                x = 0
+            end
+
+            function __init__()
+                include(joinpath(@__DIR__, "Baz26028.jl"))
+            end
+
+            end
+            """)
+        write(joinpath(load_path, "Baz26028.jl"),
+            """
+            module Baz26028
+            import Foo26028.Bar26028.x
+            end
+            """)
+
+        pushfirst!(LOAD_PATH, load_path)
+        pushfirst!(DEPOT_PATH, load_cache_path)
+
+        Base.compilecache(Base.PkgId("Foo26028"))
+        @test_nowarn @eval using Foo26028
+    finally
+        rm(load_path, recursive=true)
+        rm(load_cache_path, recursive=true)
+    end
+end
+
+
 end # !withenv