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Fix deadlock in nix-store when max-connections=1

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This fixes a bug I encountered where `nix-store -qR` will deadlock when
the `--include-outputs` flag is passed and `max-connections=1`.

The deadlock occurs because `RemoteStore::queryDerivationOutputs` takes
the only connection from the connection pool and uses it to check the
daemon version. If the version is new enough, it calls
`Store::queryDerivationOutputs`, which eventually calls
`RemoteStore::queryPartialDerivationOutputMap`, where we take another
connection from the connection pool to check the version again. Because
we still haven't released the connection from the caller, this waits for
a connection to be available, causing a deadlock.

This diff solves the issue by using `getProtocol` to check the protocol
version in the caller `RemoteStore::queryDerivationOutputs`, which
immediately frees the connection back to the pool before returning the
protocol version. That way we've already freed the connection by the
time we call `RemoteStore::queryPartialDerivationOutputMap`.
This commit is contained in:
Jake Waksbaum 2020-11-16 02:35:50 -05:00
parent 258e5338d6
commit 01db455733
1 changed files with 2 additions and 2 deletions
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4
src/libstore/remote-store.cc
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@ -409,10 +409,10 @@ StorePathSet RemoteStore::queryValidDerivers(const StorePath & path)
StorePathSet RemoteStore::queryDerivationOutputs(const StorePath & path)
{
auto conn(getConnection());
if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 0x16) {
if (GET_PROTOCOL_MINOR(getProtocol()) >= 0x16) {
return Store::queryDerivationOutputs(path);
}
auto conn(getConnection());
conn->to << wopQueryDerivationOutputs << printStorePath(path);
conn.processStderr();
return worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});