[Bug] Kernel panic on Intel Mac with AMD dGPU during heavy parallel Claude Code CLI usage - WindowServer watchdog timeout

Status Open
Reported on v2.1.201
Maintainer reply None cached
Activity 3 comments · opened Jul 6, 2026

Bug Description
Title: Intel MacBook Pro (AMD dGPU) kernel panics correlating with heavy/parallel Claude Code CLI usage — WindowServer watchdog timeout

Environment: MacBook Pro 16" 2019, Intel Core i9-9980HK, 32GB RAM, macOS 26.5.2 (25F84), AMD Radeon Pro 5500M + Intel UHD 630 (auto-switching), iTerm2, Claude Code CLI.

Observed: 2 full kernel panics within ~7 hours (2026-07-01 13:34:58 UTC, 2026-07-01 20:38:37 UTC), both panic(...): userspace watchdog timeout: no successful checkins from WindowServer (2 induced crashes) in 120 seconds. Followed by 20 AMD GPU Reset events over the next ~7.5 hours.

One panic occurred 55 seconds after invoking the Workflow tool under Fable 5 + /effort ultracode (multi-agent parallel orchestration mode). The other panic occurred during Opus 4.8/Sonnet 5 usage without Fable 5 active, so this is not exclusively tied to one model — but it suggests sustained heavy/parallel CLI tool-use load (multiple concurrent sessions, high-frequency terminal output, Workflow multi-agent spawning) stresses WindowServer/AMD GPU driver stability on Intel Macs with discrete GPUs, not observed on Apple Silicon.

Ask: Any guidance on reducing terminal-rendering / concurrent-process load from Claude Code on Intel + dGPU Macs, or whether Workflow's concurrency cap should be more conservative on such hardware.

Environment Info

  • Platform: darwin
  • Terminal: iTerm.app
  • Version: 2.1.201
  • Feedback ID: 3e45af88-e1d4-4781-a046-4feb9d5c75b1

Errors

View original on GitHub ↗

3 Comments

kikalex · 1 month ago

<h2>English Comment (Ready to Post)</h2><p>Same machine, same macOS version, same GPU — but I'm <strong>not</strong> using Claude Code at all. This confirms the root cause is macOS 26.5.2's AMD GPU driver, not any specific application.</p><p><strong>Machine:</strong> MacBook Pro 16" 2019 (MacBookPro16,1), Intel Core i9, 64GB RAM
<strong>GPU:</strong> AMD Radeon Pro 5500M + Intel UHD 630
<strong>macOS:</strong> 26.5.2 (25F84)</p><p><strong>Timeline — directly correlates with the 26.5.2 update:</strong></p><ul><li>June 2: Installed macOS 26.5.1 (25F80)</li></ul><ul><li>June 2 – June 29: <strong>28 days, zero crashes</strong></li></ul><ul><li>June 30: macOS 26.5.2 (25F84) released → <strong>first GPU Reset at 13:34, first shutdown stall at 17:52, same day</strong></li></ul><ul><li>June 30 – July 7: 9 shutdown stalls + 20+ GPU Resets, all on AMD 5500M</li></ul><p><strong>Controlled experiments (gpuswitch):</strong></p>
Setting | Result
-- | --
gpuswitch 2 (auto, default) | Random crashes during normal use and sleep/wake
gpuswitch 1 (forced dGPU) | 11 GPU Resets in 12 minutes, WindowServer crash — AMD GPU is fundamentally unstable under 26.5.2
gpuswitch 0 (forced iGPU) | No crashes during normal use, but sleep/wake still triggers kernel panic (PCIe power state recovery fails)
gpuswitch 0 + disablesleep 1 | Stable — GPU Resets still occur occasionally but self-recover without system crash

<p><strong>Key findings:</strong></p><ol><li><strong>Not application-specific:</strong> I don't use Claude Code. Crashes happen with WindowServer, mediaanalysisd, and other system processes — whatever touches the AMD GPU.</li></ol><ol><li><strong>Sleep/wake is a major trigger:</strong> Panic logs show <code>PCIeUp link state: 0x1614</code> on every crash. The AMD GPU fails to recover its PCIe link after wake, causing the watchdog timeout. This matches <code>Signature: 2, Restart Channel: 18 VMPT</code> in GPU Reset reports.</li></ol><ol><li><strong>Started exactly with 26.5.2:</strong> 28 days of zero crashes on 26.5.1, then immediate failures on 26.5.2 release day. The update clearly changed AMD GPU power management / PCIe link recovery behavior.</li></ol><ol><li><strong>Workaround:</strong> <code>sudo pmset -a gpuswitch 0</code> + <code>sudo pmset -a disablesleep 1</code> keeps the machine stable, but disabling sleep is not a real fix.</li></ol><p><strong>Panic log excerpt:</strong></p><pre><code></code></pre><p>This is a macOS 26.5.2 regression affecting all MacBookPro16,1 with AMD 5500M, independent of workload. Would appreciate Apple addressing this in 26.5.3 or 26.6.</p><sc-clipboard block-data="[{&quot;blockId&quot;:&quot;d4A5FlN65Bxdn1X8ifnRSl&quot;,&quot;blockSubtree&quot;:{&quot;block&quot;:{&quot;d4A5FlN65Bxdn1X8ifnRSl&quot;:{&quot;role&quot;:&quot;editor&quot;,&quot;value&quot;:{&quot;id&quot;:&quot;d4A5FlN65Bxdn1X8ifnRSl&quot;,&quot;parentId&quot;:&quot;&quot;,&quot;type&quot;:&quot;header2&quot;,&quot;props&quot;:{&quot;title&quot;:[[&quot;English Comment (Ready to Post)&quot;,null]]},&quot;children&quot;:[],&quot;parentTable&quot;:&quot;block&quot;,&quot;enabled&quot;:true}}}}},{&quot;blockId&quot;:&quot;SXaX4RUoCbLVQKa3GoxD0n&quot;,&quot;blockSubtree&quot;:{&quot;block&quot;:{&quot;SXaX4RUoCbLVQKa3GoxD0n&quot;:{&quot;role&quot;:&quot;editor&quot;,&quot;value&quot;:{&quot;id&quot;:&quot;SXaX4RUoCbLVQKa3GoxD0n&quot;,&quot;parentId&quot;:&quot;&quot;,&quot;type&quot;:&quot;text&quot;,&quot;props&quot;:{&quot;title&quot;:[[&quot;Same machine, same macOS version, same GPU — but I'm &quot;,null],[&quot;not&quot;,[[&quot;b&quot;]]],[&quot; using Claude Code at all. 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Would appreciate Apple addressing this in 26.5.3 or 26.6.&quot;,null]]},&quot;children&quot;:[],&quot;parentTable&quot;:&quot;block&quot;,&quot;enabled&quot;:true}}}}}]"></sc-clipboard>

shigechika · 1 month ago

@kikalex Thanks for the detailed gpuswitch A/B testing — that pins down the actual cause.

I need to correct my own report: the "Workflow tool 55s before panic" correlation I flagged was likely coincidental. My other panic that same day happened during plain Opus/Sonnet use, no Fable/Workflow involved — same panic_string both times. So this looks like your macOS 26.5.2 AMD dGPU PCIe link regression, not Claude-Code-specific.

I've applied gpuswitch 0 + disablesleep 1 a few days ago (same MacBookPro16,1 / 5500M / 26.5.2). No panics/GPU Resets so far, but too early to call it resolved — will report back.

shigechika · 1 month ago

Follow-up as promised: the workaround (gpuswitch 0 + disablesleep 1) held for 12 days, then panicked again this morning — same panic_string (WindowServer watchdog timeout).

Notable details from the logs:

  • GPU Reset storm on the AMD 5500M: 20 resets in 49 minutes (intervals shrinking 8min → 90s), ending in the panic
  • The dGPU was completely idle: no external display, Application: field empty, all command processors IDLE (CPGraphics= IDLE CPCompute= IDLE), 130 RSMU timeout events — so this fires even with zero workload, further confirming it's the 26.5.2 driver's power management itself
  • WindowServer's hang was inside AMDRadeonX6000* frames — even under gpuswitch 0 it keeps a handle to the AMD Metal driver, so a dGPU firmware death still takes it down

So gpuswitch 0 + disablesleep 1 reduces frequency (0 resets in 12 days vs. daily storms before) but doesn't fully prevent it. Still on 26.5.2 — no fix available via softwareupdate as of today.