bisecting fixing commit since 63bbbcd8ed53c404649e0b4248c1e5d42c41ac97 building syzkaller on 34bf9440bd06034f86b5d9ac8afbf078129cbdae testing commit 63bbbcd8ed53c404649e0b4248c1e5d42c41ac97 with gcc (GCC) 8.1.0 kernel signature: 425fb3aca441e33988b5aa09d5078c32f7db4296d1cb23d1788d726cf1afb14a run #0: crashed: INFO: rcu detected stall in do_iter_readv_writev run #1: crashed: INFO: rcu detected stall in ext4_file_write_iter 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 ext4_file_write_iter run #5: crashed: INFO: rcu detected stall in sys_sendfile64 run #6: crashed: INFO: rcu detected stall in ext4_file_write_iter run #7: crashed: INFO: rcu detected stall in corrupted run #8: crashed: INFO: rcu detected stall in ext4_file_write_iter run #9: crashed: INFO: rcu detected stall in sys_sendfile64 testing current HEAD 31acccdc877486a649a86d37725a15175fcd5ed6 testing commit 31acccdc877486a649a86d37725a15175fcd5ed6 with gcc (GCC) 8.1.0 kernel signature: c66d40be24be193073ec952ca098ea2efad241542671c4d5582096610a56cab8 run #0: crashed: INFO: rcu detected stall in ext4_file_write_iter run #1: crashed: INFO: rcu detected stall in ext4_file_write_iter 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 corrupted 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 ext4_file_write_iter run #8: crashed: INFO: rcu detected stall in ext4_file_write_iter run #9: crashed: INFO: rcu detected stall in sys_sendfile64 revisions tested: 2, total time: 26m17.933614651s (build: 16m20.367410084s, test: 9m1.896763759s) the crash still happens on HEAD commit msg: Linux 4.19.157 crash: INFO: rcu detected stall in sys_sendfile64 IPv6: ADDRCONF(NETDEV_UP): veth1_to_hsr: link is not ready IPv6: ADDRCONF(NETDEV_UP): veth1_to_hsr: link is not ready IPv6: ADDRCONF(NETDEV_UP): vxcan1: link is not ready 8021q: adding VLAN 0 to HW filter on device batadv0 rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: (detected by 0, t=10502 jiffies, g=4173, q=542) rcu: All QSes seen, last rcu_preempt kthread activity 10503 (4294951773-4294941270), jiffies_till_next_fqs=1, root ->qsmask 0x0 syz-executor.3 R running task 26968 7132 6223 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:kfree+0x11a/0x220 mm/slab.c:3823 Code: 1f 44 00 00 e8 47 d6 d4 ff 5b 41 5c 41 5d 41 5e 5d c3 e8 39 d9 d4 ff 48 83 3d 09 90 7f 06 00 0f 84 07 01 00 00 4c 89 e7 57 9d <0f> 1f 44 00 00 5b 41 5c 41 5d 41 5e 5d c3 4c 89 f2 48 89 de 4c 89 RSP: 0018:ffff888092177958 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13 RAX: 0000000000000007 RBX: ffff888097153440 RCX: 1ffff1101627691d RDX: 0000000000000000 RSI: ffff8880b13b48c8 RDI: 0000000000000286 RBP: ffff888092177978 R08: ffff8880b13b48e8 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000286 R13: ffff88813bf1e7c0 R14: ffffffff81a5b9f0 R15: 0000000000000000 iter_file_splice_write+0x4a0/0xc30 fs/splice.c:777 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:00007f79f2525c78 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: 00007f79f25266d4 R13: 00000000004c691d R14: 00000000004db8a8 R15: 00000000ffffffff rcu: rcu_preempt kthread starved for 10538 jiffies! g4173 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