bisecting fixing commit since 882e8691130bd75fd0ab540896db26e25eedf476 building syzkaller on c692b5bdabba075211571ae6dfe3453a8193591a testing commit 882e8691130bd75fd0ab540896db26e25eedf476 with gcc (GCC) 8.1.0 run #0: crashed: INFO: rcu detected stall in __do_softirq run #1: crashed: INFO: rcu detected stall in __do_softirq run #2: OK run #3: OK run #4: OK run #5: OK run #6: OK run #7: OK run #8: OK run #9: OK testing current HEAD 0e9d28bc6c81f47f94979ec7d0ab6ac42345fcee testing commit 0e9d28bc6c81f47f94979ec7d0ab6ac42345fcee with gcc (GCC) 8.1.0 run #0: crashed: INFO: rcu detected stall in kvm_vcpu_ioctl run #1: OK run #2: OK run #3: OK run #4: OK run #5: OK run #6: OK run #7: OK run #8: OK run #9: OK revisions tested: 2, total time: 34m8.992971896s (build: 11m56.473176295s, test: 20m14.649215319s) the crash still happens on HEAD crash: INFO: rcu detected stall in kvm_vcpu_ioctl rcu: INFO: rcu_preempt self-detected stall on CPU rcu: 1-...!: (1 GPs behind) idle=ec6/1/0x4000000000000002 softirq=82181/82182 fqs=6 (t=17047 jiffies g=51769 q=137207) NMI backtrace for cpu 1 CPU: 1 PID: 737 Comm: syz-executor.4 Not tainted 5.4.0-rc3-next-20191015 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x113/0x167 lib/dump_stack.c:113 nmi_cpu_backtrace.cold.7+0x4b/0x84 lib/nmi_backtrace.c:101 nmi_trigger_cpumask_backtrace+0x18b/0x1b7 lib/nmi_backtrace.c:62 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38 trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline] rcu_dump_cpu_stacks+0x16f/0x1bc kernel/rcu/tree_stall.h:254 print_cpu_stall kernel/rcu/tree_stall.h:455 [inline] check_cpu_stall kernel/rcu/tree_stall.h:529 [inline] rcu_pending kernel/rcu/tree.c:2795 [inline] rcu_sched_clock_irq.cold.84+0x4fb/0xc3e kernel/rcu/tree.c:2244 update_process_times+0x23/0x50 kernel/time/timer.c:1726 tick_sched_handle+0x77/0x140 kernel/time/tick-sched.c:167 tick_sched_timer+0x43/0x100 kernel/time/tick-sched.c:1299 __run_hrtimer kernel/time/hrtimer.c:1514 [inline] __hrtimer_run_queues+0x32f/0xb50 kernel/time/hrtimer.c:1576 hrtimer_interrupt+0x2df/0x760 kernel/time/hrtimer.c:1638 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1110 [inline] smp_apic_timer_interrupt+0x163/0x5f0 arch/x86/kernel/apic/apic.c:1135 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830 RIP: 0010:should_resched arch/x86/include/asm/preempt.h:102 [inline] RIP: 0010:__local_bh_enable_ip+0x193/0x260 kernel/softirq.c:196 Code: 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 c8 00 00 00 48 83 3d 16 39 13 07 00 74 5b fb 66 0f 1f 44 00 00 <65> 8b 05 5e 6c c2 7e 85 c0 75 05 e8 ad c7 c0 ff 5b 41 5c 41 5d 5d RSP: 0018:ffff8880a22579e0 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13 RAX: dffffc0000000000 RBX: 0000000000000200 RCX: 0000000000000006 RDX: 1ffffffff10a595e RSI: 0000000000000008 RDI: ffffffff8852caf0 RBP: ffff8880a22579f8 R08: 0000000000000006 R09: fffffbfff138d348 R10: fffffbfff138d347 R11: ffffffff89c69a3f R12: ffffffff810b7d91 R13: ffff8880921f6040 R14: ffff8880a2257a68 R15: ffff88809b034380 local_bh_enable include/linux/bottom_half.h:32 [inline] fpregs_unlock arch/x86/include/asm/fpu/api.h:41 [inline] kvm_put_guest_fpu+0x1e7/0x4d0 arch/x86/kvm/x86.c:8435 kvm_arch_vcpu_ioctl_run+0x65a/0x1340 arch/x86/kvm/x86.c:8500 kvm_vcpu_ioctl+0x507/0xaf0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2765 vfs_ioctl fs/ioctl.c:47 [inline] file_ioctl fs/ioctl.c:539 [inline] do_vfs_ioctl+0x196/0x1150 fs/ioctl.c:726 ksys_ioctl+0x62/0x90 fs/ioctl.c:743 __do_sys_ioctl fs/ioctl.c:750 [inline] __se_sys_ioctl fs/ioctl.c:748 [inline] __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:748 do_syscall_64+0xca/0x5d0 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x459829 Code: fd b7 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 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007fd20ad21c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459829 RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000005 RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007fd20ad226d4 R13: 00000000004c2bcf R14: 00000000004d6150 R15: 00000000ffffffff