Description of problem: Discovered this by accident on a 2 core x 2 thread i7 CPU: umbus:~$ lscpu Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Byte Order: Little Endian CPU(s): 4 On-line CPU(s) list: 0-3 Thread(s) per core: 2 Core(s) per socket: 2 Socket(s): 1 NUMA node(s): 1 Vendor ID: GenuineIntel CPU family: 6 Model: 78 Model name: Intel(R) Core(TM) i7-6600U CPU @ 2.60GHz Stepping: 3 CPU MHz: 499.877 CPU max MHz: 3400.0000 CPU min MHz: 400.0000 BogoMIPS: 5616.00 Virtualization: VT-x L1d cache: 32K L1i cache: 32K L2 cache: 256K L3 cache: 4096K NUMA node0 CPU(s): 0-3 Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf tsc_known_freq pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch epb intel_pt tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm mpx rdseed adx smap clflushopt xsaveopt xsavec xgetbv1 xsaves dtherm ida arat pln pts hwp hwp_notify hwp_act_window hwp_epp Version-Release number of selected component (if applicable): kernel-4.11.3-202.fc25.x86_64 How reproducible: Occurred 2 times in 2 attempts. Steps to Reproduce: 1. Offline cpu1 (Core 0, thread 1) # echo 0 > /sys/devices/system/cpu/cpu1/online 2. Online cpu1 again # echo 1 > /sys/devices/system/cpu/cpu1/online 3. Offline cpu3 (Core 1, thread 1) # echo 0 > /sys/devices/system/cpu/cpu3/online Actual results: System freezes hard. No kdump generated. Expected results: End up with CPUs 0,1,2 online, CPU 3 offline. Additional info: Toggling cpu3 then cpu 1 doesn't seem to have the same effect.
Created attachment 1287200 [details] /proc/cpuinfo contents for reference
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