100% CPU infinite loop when browser context becomes unresponsive

[neoncapy]

Summary

The NotebookLM MCP server can get stuck in an infinite loop consuming 100% CPU for days when the underlying browser context becomes unresponsive or enters a zombie state.

Observed Behavior

• Process running at 100% CPU continuously for 80+ hours (4834 minutes CPU time)
• • Only resolved by kill -9 (regular kill was ineffective)
• • • Process command: node /Users/.../.npm/_npx/.../node_modules/.bin/notebooklm-mcp

Root Cause Analysis

After examining the source code, the issue appears to be in page-utils.js in the waitForLatestAnswer() function:

while (Date.now() < deadline) {  // 2 minute timeout
    pollCount++;
    // ... polling logic ...
    await page.waitForTimeout(pollIntervalMs);  // Should wait 1 second
}

What happens:

1. The Chromium browser (managed by Patchright) becomes unresponsive or enters a bad state
2. 2. page.waitForTimeout(1000) returns immediately instead of waiting 1 second (because the browser connection is broken)
3. 3. The while loop becomes a tight spin loop with no actual waiting
4. 4. The 2-minute deadline never triggers because Date.now() is called, but the CPU is saturated
      Why detection fails:
      The recovery logic checks for specific error messages:

if (/has been closed|Target .* closed|Browser has been closed|Context .* closed/i.test(msg))

But a zombie browser (unresponsive but not cleanly closed) doesn't trigger these patterns.

Suggested Fixes

1. Add maximum poll count limit:
3. const MAX_POLLS = 7200; // 2 hours max at 1s intervals
4. while (Date.now() < deadline && pollCount < MAX_POLLS) {
6. Add health check for the page:
8. try {

9. await page.evaluate(() => true);  // Simple aliveness check
   

10. } catch {

11. throw new Error("Browser page unresponsive");
    

12. }
14. Exponential backoff on repeated empty polls

Environment

• Node.js: v20+
• • notebooklm-mcp version: 1.2.1
• • • OS: macOS (Darwin)
• • • • Patchright/Playwright version: 1.48.2

[joaocarlos]

Does this only happen with Chromium? Does it also happen in Chrome? Perhaps, if you know the root cause, you can provide a pull request.

[eirisdg]

Same here in MacOs with m5: