fix: avoid deadlock when entering a span

src/layer.rs

@@ -13,6 +13,7 @@ use std::time::Instant;
 use std::{any::TypeId, borrow::Cow};
 use std::{fmt, vec};
 use std::{marker, mem::take};
+use tracing::Dispatch;
 use tracing_core::span::{self, Attributes, Id, Record};
 use tracing_core::{field, Event, Subscriber};
 #[cfg(feature = "tracing-log")]
@@ -1079,10 +1080,16 @@ where
             status,
         } = take(&mut otel_data.state)
         {
-            let mut span = builder.start_with_context(&self.tracer, &parent_cx);
-            span.set_status(status);
-            let current_cx = parent_cx.with_span(span);
-            otel_data.state = OtelDataState::Context { current_cx };
+            // We purposefully disable all tracing inside this call. Whoever called this is most
+            // likely holding `ExtensionsMut` so if anything inside any of the opentelemetry
+            // functions tries to log anything and any layer (including this one) tries to get the
+            // extensions again, we get a deadlock.
+            tracing::dispatcher::with_default(&Dispatch::none(), || {
+                let mut span = builder.start_with_context(&self.tracer, &parent_cx);
+                span.set_status(status);
+                let current_cx = parent_cx.with_span(span);
+                otel_data.state = OtelDataState::Context { current_cx };
+            });
         }
     }
 
@@ -1477,7 +1484,9 @@ where
                     parent_cx,
                     status,
                 } => {
-                    // Don't create the context here just to get a SpanRef since it's costly
+                    // We're not holding the extensions lock here so it's fine to just call to
+                    // opentelemetry and let it log whatever it wants. If we had a lock, we'd have
+                    // to set the default `Dispatch` to none to prevent deadlocks.
                     let mut span = builder.start_with_context(&self.tracer, &parent_cx);
                     if let Some(timings) = timings {
                         span.set_attributes(timings)