Possible deadlock caused by substitution, outputLocks

[roberth]

Describe the bug

Guix have fixed a deadlock, apparently caused by the substitution goal not releasing locks soon enough.

Steps To Reproduce

Expected behavior

Possible fix:

diff on guix:

diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index 43a8a371846..edd01bab34d 100644
--- a/nix/libstore/build.cc
+++ b/nix/libstore/build.cc
@@ -1200,6 +1200,7 @@ void DerivationGoal::tryToBuild()
     if (buildMode != bmCheck && validPaths.size() == drv.outputs.size()) {
         debug(format("skipping build of derivation `%1%', someone beat us to it") % drvPath);
         outputLocks.setDeletion(true);
+        outputLocks.unlock();
         done(BuildResult::AlreadyValid);
         return;
     }
@@ -3070,6 +3071,7 @@ void SubstitutionGoal::tryToRun()
     if (!repair && worker.store.isValidPath(storePath)) {
         debug(format("store path `%1%' has become valid") % storePath);
         outputLock->setDeletion(true);
+        outputLock.reset();
         amDone(ecSuccess);
         return;
     }

Metadata

Additional context

Checklist

• checked latest Nix manual (source)
• checked open bug issues and pull requests for possible duplicates

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[Mic92]

#12160

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2025-01-08-nix-team-meeting-minutes-207/58523/1