tor-browser

commit 26a55e242dd744539791dc24d9b396f22dfed603
parent bc6c7da176c6f6383491b72494307a3593257323
Author: Kershaw Chang <kershaw@mozilla.com>
Date:   Wed, 26 Nov 2025 09:27:03 +0000

Bug 2001721 - Prevent busy loop when tunneled connection returns WOULD_BLOCK, r=necko-reviewers,valentin

When a tunneled connection returns WOULD_BLOCK, the consumer calls AyncWait() and we enqueue the stream on the ready queue. We then call ForceSend() -> ProcessOutput() and immediately attempt to send again, which still would block, causing the stream to be re-queued and retried in a busy loop.

This patch introduces a mBlockedByFlowControl flag that is only cleared when neqo notifies us the stream is writable. While the flag is set, we skip send attempts. This avoids the busy waiting.

Differential Revision: https://phabricator.services.mozilla.com/D274000

Diffstat:
M
netwerk/protocol/http/Http3Session.cpp
 | 
15
+++++++++++++++
M
netwerk/protocol/http/Http3Stream.cpp
 | 
1
+
M
netwerk/protocol/http/Http3StreamBase.h
 | 
4
++++

3 files changed, 20 insertions(+), 0 deletions(-)
diff --git a/netwerk/protocol/http/Http3Session.cpp b/netwerk/protocol/http/Http3Session.cpp
@@ -589,6 +589,7 @@ nsresult Http3Session::ProcessEvents() {
 
         if (stream) {
           StreamReadyToWrite(stream);
+          stream->SetBlockedByFlowControl(false);
         }
       } break;
       case Http3Event::Tag::Reset:
@@ -1823,11 +1824,18 @@ nsresult Http3Session::SendData(nsIUDPSocket* socket) {
   nsresult rv = NS_OK;
   RefPtr<Http3StreamBase> stream;
 
+  nsTArray<RefPtr<Http3StreamBase>> blockedStreams;
+
   // Step 1)
   while (CanSendData() && (stream = mReadyForWrite.PopFront())) {
     LOG(("Http3Session::SendData call ReadSegments from stream=%p [this=%p]",
          stream.get(), this));
     stream->SetInTxQueue(false);
+    if (stream->BlockedByFlowControl()) {
+      LOG(("stream %p blocked by flow control", stream.get()));
+      blockedStreams.AppendElement(stream);
+      continue;
+    }
     rv = stream->ReadSegments();
 
     // on stream error we return earlier to let the error be handled.
@@ -1863,6 +1871,13 @@ nsresult Http3Session::SendData(nsIUDPSocket* socket) {
   if (NS_FAILED(rv)) {
     return rv;
   }
+
+  // Put the blocked streams back to the queue, since they are ready to write.
+  for (const auto& stream : blockedStreams) {
+    mReadyForWrite.Push(stream);
+    stream->SetInTxQueue(true);
+  }
+
   rv = ProcessEvents();
 
   // Let the connection know we sent some app data successfully.
diff --git a/netwerk/protocol/http/Http3Stream.cpp b/netwerk/protocol/http/Http3Stream.cpp
@@ -184,6 +184,7 @@ nsresult Http3Stream::OnReadSegment(const char* buf, uint32_t count,
       rv = mSession->SendRequestBody(mStreamId, buf, count, countRead);
       if (rv == NS_BASE_STREAM_WOULD_BLOCK) {
         mSendingBlockedByFlowControlCount++;
+        mBlockedByFlowControl = true;
       }
 
       if (NS_FAILED(rv)) {
diff --git a/netwerk/protocol/http/Http3StreamBase.h b/netwerk/protocol/http/Http3StreamBase.h
@@ -59,6 +59,9 @@ class Http3StreamBase : public SupportsWeakPtr, public ARefBase {
   void SetInTxQueue(bool aValue) { mInTxQueue = aValue; }
   bool IsInTxQueue() const { return mInTxQueue; }
 
+  void SetBlockedByFlowControl(bool aValue) { mBlockedByFlowControl = aValue; }
+  bool BlockedByFlowControl() const { return mBlockedByFlowControl; }
+
  protected:
   ~Http3StreamBase();
 
@@ -71,6 +74,7 @@ class Http3StreamBase : public SupportsWeakPtr, public ARefBase {
   bool mFin{false};
   bool mResetRecv{false};
   bool mInTxQueue{false};
+  bool mBlockedByFlowControl{false};
 };
 
 }  // namespace mozilla::net