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RemoteStore::addToStore(): Fix race between stderrThread and NAR writer

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As pointed out by @B4dM4n, the call to to.flush() on stderrThread is
unsafe because the NAR writer thread is also writing to 'to'.

Fixes #3943.
This commit is contained in:
Eelco Dolstra 2020-08-27 14:48:08 +02:00
parent 3ccf3801fb
commit a0f19d9f3a
3 changed files with 13 additions and 8 deletions
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13
src/libstore/remote-store.cc
View file

@ -284,9 +284,9 @@ struct ConnectionHandle
RemoteStore::Connection * operator -> () { return &*handle; } RemoteStore::Connection * operator -> () { return &*handle; }
void processStderr(Sink * sink = 0, Source * source = 0) void processStderr(Sink * sink = 0, Source * source = 0, bool flush = true)
{ {
auto ex = handle->processStderr(sink, source); auto ex = handle->processStderr(sink, source, flush);
if (ex) { if (ex) {
daemonException = true; daemonException = true;
std::rethrow_exception(ex); std::rethrow_exception(ex);
@ -535,6 +535,8 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 23) { if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 23) {
conn->to.flush();
std::exception_ptr ex; std::exception_ptr ex;
struct FramedSink : BufferedSink struct FramedSink : BufferedSink
@ -574,7 +576,7 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
std::thread stderrThread([&]() std::thread stderrThread([&]()
{ {
try { try {
conn.processStderr(); conn.processStderr(nullptr, nullptr, false);
} catch (...) { } catch (...) {
ex = std::current_exception(); ex = std::current_exception();
} }
@ -884,9 +886,10 @@ static Logger::Fields readFields(Source & from)
} }
std::exception_ptr RemoteStore::Connection::processStderr(Sink * sink, Source * source) std::exception_ptr RemoteStore::Connection::processStderr(Sink * sink, Source * source, bool flush)
{ {
to.flush(); if (flush)
to.flush();
while (true) { while (true) {

2
src/libstore/remote-store.hh
View file

@ -114,7 +114,7 @@ protected:
virtual ~Connection(); virtual ~Connection();
std::exception_ptr processStderr(Sink * sink = 0, Source * source = 0); std::exception_ptr processStderr(Sink * sink = 0, Source * source = 0, bool flush = true);
}; };
ref<Connection> openConnectionWrapper(); ref<Connection> openConnectionWrapper();

6
src/libutil/serialise.hh
View file

@ -23,7 +23,8 @@ struct Sink
}; };
/* A buffered abstract sink. */ /* A buffered abstract sink. Warning: a BufferedSink should not be
used from multiple threads concurrently. */
struct BufferedSink : virtual Sink struct BufferedSink : virtual Sink
{ {
size_t bufSize, bufPos; size_t bufSize, bufPos;
@ -66,7 +67,8 @@ struct Source
}; };
/* A buffered abstract source. */ /* A buffered abstract source. Warning: a BufferedSink should not be
used from multiple threads concurrently. */
struct BufferedSource : Source struct BufferedSource : Source
{ {
size_t bufSize, bufPosIn, bufPosOut; size_t bufSize, bufPosIn, bufPosOut;