Merge pull request #26595 from vespa-engine/vekterli/take-queue-mutex-on-flush

Ensure proper memory visibility on distributor stripe flush

1 files changed, 6 insertions, 0 deletions

diff --git a/storage/src/vespa/storage/distributor/distributor_stripe.cpp b/storage/src/vespa/storage/distributor/distributor_stripe.cpp
index 782dd9d7e12..616fd77fdd7 100644
--- a/storage/src/vespa/storage/distributor/distributor_stripe.cpp
+++ b/storage/src/vespa/storage/distributor/distributor_stripe.cpp
@@ -127,6 +127,12 @@ void DistributorStripe::send_shutdown_abort_reply(const std::shared_ptr<api::Sto
 }
 
 void DistributorStripe::flush_and_close() {
+    // This function is called from a different thread than that of the stripe
+    // itself, so we need to take the same mutex to form a memory visibility pair.
+    // It is important that no flushing ever sends any _requests_, as these
+    // will most likely synchronously be bounced by the already shut down RPC
+    // layer, causing a deadlock when the response call chain arrives back here.
+    std::lock_guard lock(_external_message_mutex);
     for (auto& msg : _messageQueue) {
         if (!msg->getType().isReply()) {
             send_shutdown_abort_reply(msg);