bisecting fixing commit since 63bbbcd8ed53c404649e0b4248c1e5d42c41ac97 building syzkaller on 34bf9440bd06034f86b5d9ac8afbf078129cbdae testing commit 63bbbcd8ed53c404649e0b4248c1e5d42c41ac97 with gcc (GCC) 8.1.0 kernel signature: afc9f1e472def9c215cb4ed7ed498bc6cb44b742b2b67d8da5ca3c164249adb6 run #0: crashed: INFO: rcu detected stall in sys_sendfile64 run #1: crashed: INFO: rcu detected stall in sys_sendfile64 run #2: crashed: INFO: rcu detected stall in sys_sendfile64 run #3: crashed: INFO: rcu detected stall in sys_sendfile64 run #4: crashed: INFO: rcu detected stall in sys_sendfile64 run #5: crashed: INFO: rcu detected stall in sys_sendfile64 run #6: crashed: INFO: rcu detected stall in sys_sendfile64 run #7: crashed: INFO: rcu detected stall in sys_sendfile64 run #8: crashed: INFO: rcu detected stall in ext4_file_write_iter run #9: crashed: INFO: rcu detected stall in ext4_file_write_iter testing current HEAD c14d30dc9987047b439b03d6e6db7d54d9f7f180 testing commit c14d30dc9987047b439b03d6e6db7d54d9f7f180 with gcc (GCC) 8.1.0 kernel signature: 455fbeca8abd5ab1afee6a45bb2f8022a180677d57029aa79a089b5949ce4311 run #0: crashed: INFO: rcu detected stall in sys_sendfile64 run #1: crashed: INFO: rcu detected stall in sys_sendfile64 run #2: crashed: INFO: rcu detected stall in sys_sendfile64 run #3: crashed: INFO: rcu detected stall in sys_sendfile64 run #4: crashed: INFO: rcu detected stall in sys_sendfile64 run #5: crashed: INFO: rcu detected stall in sys_sendfile64 run #6: crashed: INFO: rcu detected stall in corrupted run #7: crashed: INFO: rcu detected stall in ext4_file_write_iter run #8: crashed: INFO: rcu detected stall in sys_sendfile64 run #9: crashed: INFO: rcu detected stall in ext4_file_write_iter revisions tested: 2, total time: 29m16.852895459s (build: 17m55.574003139s, test: 10m7.46489106s) the crash still happens on HEAD commit msg: Linux 4.19.139 crash: INFO: rcu detected stall in ext4_file_write_iter IPv6: ADDRCONF(NETDEV_UP): vxcan1: link is not ready IPv6: ADDRCONF(NETDEV_UP): veth0_to_team: link is not ready IPv6: ADDRCONF(NETDEV_UP): veth1_to_team: link is not ready IPv6: ADDRCONF(NETDEV_UP): veth0_to_hsr: link is not ready rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: (detected by 0, t=10502 jiffies, g=4785, q=273) rcu: All QSes seen, last rcu_preempt kthread activity 10503 (4294952276-4294941773), jiffies_till_next_fqs=1, root ->qsmask 0x0 syz-executor.2 R running task 26968 7148 6252 0x00000000 Call Trace: sched_show_task.cold.86+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_is_held_type+0x18b/0x210 kernel/locking/lockdep.c:3947 Code: ff df 41 c7 84 24 84 08 00 00 00 00 00 00 48 89 fa 48 c1 ea 03 80 3c 02 00 75 63 48 83 3d a4 31 c6 06 00 74 30 48 89 df 57 9d <0f> 1f 44 00 00 48 83 c4 08 44 89 e8 5b 41 5c 41 5d 5d c3 48 83 c4 RSP: 0018:ffff888085f3f4c8 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13 RAX: dffffc0000000000 RBX: 0000000000000286 RCX: 1ffff11010bedec9 RDX: 1ffffffff1024161 RSI: ffffffff8819a2e0 RDI: 0000000000000286 RBP: ffff888085f3f4e8 R08: ffffed1015d44733 R09: ffffed1015d44732 R10: ffffed1015d44732 R11: ffff8880aea23993 R12: ffff888085f6e640 R13: 0000000000000000 R14: 0000000000000c6b R15: 000000000000001c lock_is_held include/linux/lockdep.h:344 [inline] ___might_sleep+0x1fe/0x2a0 kernel/sched/core.c:6161 generic_perform_write+0x35d/0x480 mm/filemap.c:3179 __generic_file_write_iter+0x201/0x580 mm/filemap.c:3287 ext4_file_write_iter+0x282/0xe60 fs/ext4/file.c:272 call_write_iter include/linux/fs.h:1821 [inline] do_iter_readv_writev+0x4ae/0x960 fs/read_write.c:681 do_iter_write+0x12a/0x510 fs/read_write.c:960 vfs_iter_write+0x5b/0xb0 fs/read_write.c:973 iter_file_splice_write+0x558/0xc30 fs/splice.c:750 do_splice_from fs/splice.c:852 [inline] direct_splice_actor+0x104/0x1c0 fs/splice.c:1025 splice_direct_to_actor+0x304/0x870 fs/splice.c:980 do_splice_direct+0x14c/0x270 fs/splice.c:1068 do_sendfile+0x481/0xd00 fs/read_write.c:1447 __do_sys_sendfile64 fs/read_write.c:1502 [inline] __se_sys_sendfile64 fs/read_write.c:1494 [inline] __x64_sys_sendfile64+0x12e/0x1e0 fs/read_write.c:1494 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x459349 Code: 7d 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 4b b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007fbb30234c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000028 RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000000459349 RDX: 0000000020000000 RSI: 0000000000000003 RDI: 0000000000000003 RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000 R10: 00008080fffffffe R11: 0000000000000246 R12: 00007fbb302356d4 R13: 00000000004c691d R14: 00000000004db8a8 R15: 00000000ffffffff rcu: rcu_preempt kthread starved for 10545 jiffies! g4785 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1 rcu: RCU grace-period kthread stack dump: rcu_preempt R running task 29544 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+0x324/0x3e0 kernel/kthread.c:246 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415