Mongodb driver deadlock in asp.net core - asp.net

Question

I have simple asp.net WebApi project with two controllers.
First controller use System.Linq and has a deadlock under heavy loading. Second use MongoDB.Driver.Linq and work great.
I used ab -c 10 -n 200000 -p post -H 'Content-Type: application/json' -T 'application/json' 'http://localhost:1989/api/SystemLinq/find'
Why using System.linq I have a deadlock?
Deadlock occurs only in case when after reading data throw new Exception. Exception I catch with IExceptionFilter. Full project https://github.com/artyukh/AspNetMongoDeadlock
Controller with deadlock
using Microsoft.AspNetCore.Mvc;
using MongoDB.Driver;
using System.Linq;
using TestDeadlock.Core;
namespace TestDeadlock.Controllers
{
[Route("api/[controller]")]
public class SystemLinqController : Controller
{
private MongoContext _context;
public SystemLinqController(MongoContext context)
{
_context = context;
}
[HttpPost]
[Route("find")]
public void Find([FromBody]AuthenticateInputDTO input)
{
var result = _context.UserSet.AsQueryable().Where(u => u.Email == input.Username).FirstOrDefault();
if (result == null)
throw new BusinessException("User not found");
}
}
}
Working controller
using Microsoft.AspNetCore.Mvc;
using MongoDB.Driver;
using MongoDB.Driver.Linq;
using TestDeadlock.Core;
namespace TestDeadlock.Controllers
{
[Route("api/[controller]")]
public class MongoLinqController : Controller
{
private MongoContext _context;
public MongoLinqController(MongoContext context)
{
_context = context;
}
[HttpPost]
[Route("find")]
public void Find([FromBody]AuthenticateInputDTO input)
{
var result = _context.UserSet.AsQueryable().Where(u => u.Email == input.Username).FirstOrDefault();
if (result == null)
throw new BusinessException("User not found");
}
}
}
ConfigureServices
public void ConfigureServices(IServiceCollection services)
{
var appSettings = Configuration.GetSection("AppSettings");
// Add framework services.
services.AddMvc(options =>
{
options.Filters.Add(new GlobalExceptionFilter());
});
services.AddMvc();
services.Configure<MongoSettings>(options =>
{
options.ConnectionString
= Configuration.GetSection("MongoConnection:ConnectionString").Value;
options.Database
= Configuration.GetSection("MongoConnection:Database").Value;
});
services.AddSingleton<MongoContext>();
}
GlobalExceptionFilter
public class GlobalExceptionFilter : IExceptionFilter
{
public void OnException(ExceptionContext context)
{
Exception exception = context.Exception;
string errorMessage;
int statusCode = 500;
if (exception is BusinessException)
{
statusCode = 400;
errorMessage = exception.Message;
}
else
{
errorMessage = "Internal Error";
}
var response = new ErrorResponse
{
Message = errorMessage
};
context.Result = new ObjectResult(response)
{
StatusCode = statusCode,
DeclaredType = typeof(ErrorResponse),
ContentTypes = new MediaTypeCollection { "application/json" }
};
}
}