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worker: fix race condition in node_messaging.cc #33429

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worker: fix race condition in node_messaging.cc #33429

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worker: fix race condition in node_messaging.cc 
`AddToIncomingQueue()` relies on `owner_` only being modified with
`mutex_` being locked, but in these two places, that didn’t happen.

Modify them to use `Detach()` instead, which has the same effect
as setting `owner_ = nullptr` here, but does it with proper locking.

This race condition probably only shows up in practice when Node.js
is compiled in debug mode, because the compiler eliminates the
duplicate load in `AddToIncomingQueue()` when compiling with
optimizations enabled.
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@addaleax
addaleax committed May 16, 2020
commit 4f144ebbf8f06c10fbbe737608b1901a2c5fe157
8 changes: 3 additions & 5 deletions src/node_messaging.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -464,8 +464,7 @@ void MessagePortData::Disentangle() {
}

MessagePort::~MessagePort() {
if (data_)
data_->owner_ = nullptr;
if (data_) Detach();
}

MessagePort::MessagePort(Environment* env,
Expand Down Expand Up @@ -662,10 +661,9 @@ void MessagePort::OnMessage() {
void MessagePort::OnClose() {
Debug(this, "MessagePort::OnClose()");
if (data_) {
data_->owner_ = nullptr;
data_->Disentangle();
// Detach() returns move(data_).
Detach()->Disentangle();
}
data_.reset();
}

std::unique_ptr<MessagePortData> MessagePort::Detach() {
Expand Down