Make concurrency check handle re-entrance

Getting exception below when making Async calls.

Exception message:
A second operation started on this context before a previous operation completed. Any instance members are not guaranteed to be thread safe.

Stack trace:
   at Microsoft.EntityFrameworkCore.Internal.ConcurrencyDetector.EnterCriticalSection()
   at Microsoft.EntityFrameworkCore.Internal.ConcurrencyDetector.<EnterCriticalSectionAsync>d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Microsoft.EntityFrameworkCore.Query.Internal.AsyncLinqOperatorProvider.ExceptionInterceptor`1.EnumeratorExceptionInterceptor.<MoveNext>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Microsoft.AspNetCore.Identity.RoleManager`1.<RoleExistsAsync>d__34.MoveNext()

                    roleManager.CreateAsync(new ApplicationRole() { Name = role.Key, NormalizedName = role.Key.ToUpper(), System = true, Description = role.Value });
    }

"Microsoft.AspNetCore.Identity.EntityFrameworkCore": "1.1.0",
"Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore": "1.1.0",
"Microsoft.EntityFrameworkCore": "1.1.0",
"Microsoft.EntityFrameworkCore.Design": {
  "type": "build",
  "version": "1.1.0"
},

[ajcvickers]

@divega @anpete Should we try to make this work? It’s not multiple threads, but rather one query that has calls that are (I assume) funcletized and themselves execute queries.

[ajcvickers]

Fixed in #17089