Linux kernel hangs rarely when booting on the latest qemu Description of problem: (Downstream bug: https://bugzilla.redhat.com/show_bug.cgi?id=2213346) In Fedora we have noticed that the latest Linux kernel (rarely) hangs when booting on the latest qemu. It hangs after printing: ``` [ 0.070120] x86/cpu: User Mode Instruction Prevention (UMIP) activated [ 0.070120] Last level iTLB entries: 4KB 512, 2MB 255, 4MB 127 [ 0.070120] Last level dTLB entries: 4KB 512, 2MB 255, 4MB 127, 1GB 0 [ 0.070120] Spectre V1 : Mitigation: usercopy/swapgs barriers and __user pointer sanitization [ 0.070120] Spectre V2 : Mitigation: Retpolines [ 0.070120] Spectre V2 : Spectre v2 / SpectreRSB mitigation: Filling RSB on context switch [ 0.070120] Spectre V2 : Spectre v2 / SpectreRSB : Filling RSB on VMEXIT [ 0.070120] Spectre V2 : Enabling Speculation Barrier for firmware calls [ 0.070120] RETBleed: Mitigation: untrained return thunk [ 0.070120] Spectre V2 : mitigation: Enabling conditional Indirect Branch Prediction Barrier [ 0.070120] Speculative Store Bypass: Mitigation: Speculative Store Bypass disabled via prctl [ 0.070120] Freeing SMP alternatives memory: 48K ``` The next line which would be printed (if it didn't hang) is: ``` [ 0.070794] smpboot: CPU0: AMD Ryzen 9 3900X 12-Core Processor (family: 0x17, model: 0x71, stepping: 0x0) ``` We've seen this hang on both AMD and Intel. It probably happens one in every 300 boots. Steps to reproduce: By far the easiest way to reproduce this is to just run guestfish in a loop: ``` $ while guestfish -a /dev/null -v run >& /tmp/log; do echo -n . ; done ``` Additional information: The full qemu command is rather long but you can find it in this log file: https://bugzilla-attachments.redhat.com/attachment.cgi?id=1969620