bisecting fixing commit since a083db76118d20d070794ecf79af17843406c3f6 building syzkaller on c88c7b75a4e022b758f4b0f1bf3db8ebb2fb25e6 testing commit a083db76118d20d070794ecf79af17843406c3f6 with gcc (GCC) 8.1.0 kernel signature: 3759c4fdb7622b31e0726e7fba60b8b908693798dc3da0000c48909e93034efb run #0: crashed: INFO: rcu detected stall in kvm_vcpu_ioctl run #1: crashed: INFO: rcu detected stall in corrupted run #2: crashed: INFO: rcu detected stall in kvm_vcpu_ioctl run #3: crashed: INFO: rcu detected stall in kvm_vcpu_ioctl run #4: crashed: INFO: rcu detected stall in corrupted run #5: crashed: INFO: rcu detected stall in corrupted run #6: crashed: INFO: rcu detected stall in corrupted run #7: crashed: INFO: rcu detected stall in kvm_vcpu_ioctl run #8: crashed: INFO: rcu detected stall in kvm_vcpu_ioctl run #9: crashed: no output from test machine testing current HEAD a87f96283793d58b042618c689630db264715274 testing commit a87f96283793d58b042618c689630db264715274 with gcc (GCC) 8.1.0 kernel signature: ff18c4a22337215956e93adf1a555c64b43d9c1f1fb11513981dfb0659410091 run #0: crashed: INFO: rcu detected stall in corrupted run #1: crashed: INFO: rcu detected stall in corrupted run #2: crashed: INFO: rcu detected stall in kvm_vcpu_ioctl run #3: crashed: INFO: rcu detected stall in kvm_vcpu_ioctl run #4: crashed: INFO: rcu detected stall in kvm_vcpu_ioctl run #5: crashed: INFO: rcu detected stall in kvm_vcpu_ioctl run #6: crashed: INFO: rcu detected stall in corrupted run #7: crashed: INFO: rcu detected stall in kvm_vcpu_ioctl run #8: crashed: INFO: rcu detected stall in corrupted run #9: crashed: INFO: rcu detected stall in kvm_vcpu_ioctl revisions tested: 2, total time: 29m34.889556395s (build: 16m3.243309486s, test: 12m42.085698255s) the crash still happens on HEAD commit msg: Linux 4.19.145 crash: INFO: rcu detected stall in kvm_vcpu_ioctl L1TF CPU bug present and SMT on, data leak possible. See CVE-2018-3646 and https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1tf.html for details. kvm: emulating exchange as write rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: (detected by 1, t=10502 jiffies, g=6221, q=39) rcu: All QSes seen, last rcu_preempt kthread activity 10503 (4294953346-4294942843), jiffies_till_next_fqs=1, root ->qsmask 0x0 syz-executor.0 R running task 26472 8398 6588 0x00000800 Call Trace: sched_show_task.cold.87+0x2ee/0x35d kernel/sched/core.c:5341 print_other_cpu_stall kernel/rcu/tree.c:1430 [inline] check_cpu_stall kernel/rcu/tree.c:1557 [inline] __rcu_pending kernel/rcu/tree.c:3293 [inline] rcu_pending kernel/rcu/tree.c:3336 [inline] rcu_check_callbacks.cold.81+0xa80/0xd67 kernel/rcu/tree.c:2682 update_process_times+0x28/0x90 kernel/time/timer.c:1650 tick_sched_handle+0x77/0x140 kernel/time/tick-sched.c:168 tick_sched_timer+0x37/0xf0 kernel/time/tick-sched.c:1278 __run_hrtimer kernel/time/hrtimer.c:1401 [inline] __hrtimer_run_queues+0x2f7/0xab0 kernel/time/hrtimer.c:1463 hrtimer_interrupt+0x2df/0x760 kernel/time/hrtimer.c:1521 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1067 [inline] smp_apic_timer_interrupt+0x114/0x540 arch/x86/kernel/apic/apic.c:1092 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:894 RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:789 [inline] RIP: 0010:lock_acquire+0x1f1/0x3d0 kernel/locking/lockdep.c:3910 Code: 00 00 00 00 00 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 aa 01 00 00 48 83 3d 23 70 06 07 00 0f 84 31 01 00 00 48 8b 7d c8 57 9d <0f> 1f 44 00 00 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 65 8b RSP: 0018:ffff88809241efa0 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13 RAX: dffffc0000000000 RBX: ffff888090856240 RCX: 1ffff1101210ad67 RDX: 1ffffffff10a40b9 RSI: 0000000000000000 RDI: 0000000000000286 RBP: ffff88809241efe8 R08: 0000000000007a5d R09: 0000000000000002 R10: ffff888090856b18 R11: 0000000000000001 R12: 0000000000000000 R13: 0000000000000001 R14: 0000000000000001 R15: 0000000000000000 __might_fault+0x124/0x1b0 mm/memory.c:4638 __copy_from_user include/linux/uaccess.h:72 [inline] paging64_walk_addr_generic+0x342/0x1c60 arch/x86/kvm/paging_tmpl.h:370 paging64_walk_addr arch/x86/kvm/paging_tmpl.h:484 [inline] paging64_gva_to_gpa+0x8c/0x170 arch/x86/kvm/paging_tmpl.h:938 kvm_fetch_guest_virt+0xc3/0x170 arch/x86/kvm/x86.c:5020 __do_insn_fetch_bytes+0x34f/0x580 arch/x86/kvm/emulate.c:896 x86_decode_insn+0x146d/0x7190 arch/x86/kvm/emulate.c:5119 x86_emulate_instruction+0x6ae/0x1810 arch/x86/kvm/x86.c:6342 kvm_emulate_instruction arch/x86/kvm/x86.c:6457 [inline] handle_ud+0x97/0x240 arch/x86/kvm/x86.c:5154 handle_exception+0x79e/0xad0 arch/x86/kvm/vmx.c:7055 vmx_handle_exit+0x1b5/0x11b0 arch/x86/kvm/vmx.c:10167 vcpu_enter_guest+0xd4b/0x50a0 arch/x86/kvm/x86.c:7822 vcpu_run arch/x86/kvm/x86.c:7885 [inline] kvm_arch_vcpu_ioctl_run+0x2e9/0x1340 arch/x86/kvm/x86.c:8085 kvm_vcpu_ioctl+0x535/0xb60 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2822 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:501 [inline] do_vfs_ioctl+0x196/0x10c0 fs/ioctl.c:688 ksys_ioctl+0x62/0x90 fs/ioctl.c:705 __do_sys_ioctl fs/ioctl.c:712 [inline] __se_sys_ioctl fs/ioctl.c:710 [inline] __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:710 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x45c4f9 Code: 2d b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 fb b5 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007fe984a3fc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007fe984a406d4 RCX: 000000000045c4f9 RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000006 RBP: 000000000076bf20 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff R13: 00000000000003bf R14: 00000000004c6118 R15: 000000000076bf2c rcu: rcu_preempt kthread starved for 10555 jiffies! g6221 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1 rcu: RCU grace-period kthread stack dump: rcu_preempt R running task 29208 10 2 0x80000000 Call Trace: context_switch kernel/sched/core.c:2828 [inline] __schedule+0x78c/0x1c10 kernel/sched/core.c:3517 schedule+0x7f/0x1b0 kernel/sched/core.c:3561 schedule_timeout+0x3ab/0xe00 kernel/time/timer.c:1825 rcu_gp_kthread+0xce6/0x23d0 kernel/rcu/tree.c:2202 kthread+0x347/0x410 kernel/kthread.c:259 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415