bisecting fixing commit since 675cc038067f0e530471c56a7442935f84669d95 building syzkaller on 65a7a8540d29e72622fca06522587f7e66539fd3 testing commit 675cc038067f0e530471c56a7442935f84669d95 compiler: gcc version 8.4.1 20210217 (GCC) kernel signature: f081f6588f9a1249f28821d73367f023f53b5c8534d4b28450fc86ecec05191c run #0: crashed: INFO: task hung in grab_super run #1: crashed: INFO: task hung in grab_super run #2: crashed: INFO: task hung in grab_super run #3: crashed: INFO: task hung in grab_super run #4: crashed: INFO: task hung in grab_super run #5: crashed: INFO: task hung in grab_super run #6: crashed: INFO: task hung in grab_super run #7: crashed: INFO: task hung in grab_super run #8: crashed: INFO: task hung in grab_super run #9: crashed: INFO: task hung in grab_super run #10: crashed: INFO: task hung in grab_super run #11: crashed: INFO: task hung in grab_super run #12: crashed: INFO: task hung in grab_super run #13: crashed: INFO: task hung in grab_super run #14: crashed: INFO: task hung in grab_super run #15: crashed: INFO: task hung in grab_super run #16: crashed: INFO: task hung in grab_super run #17: crashed: INFO: task hung in grab_super run #18: crashed: no output from test machine run #19: crashed: no output from test machine testing current HEAD c2276d585654e8d573366c29c565043ec36adf63 testing commit c2276d585654e8d573366c29c565043ec36adf63 compiler: gcc version 8.4.1 20210217 (GCC) kernel signature: 44700de8f217a473f71699b9047151522da7084acfc7816e55f67763bd4aad34 all runs: crashed: INFO: task hung in grab_super revisions tested: 2, total time: 32m33.205898526s (build: 17m27.834724601s, test: 14m25.401658204s) the crash still happens on HEAD commit msg: Linux 4.19.208 crash: INFO: task hung in grab_super Bluetooth: hci3: command 0x0406 tx timeout Bluetooth: hci0: command 0x0406 tx timeout Bluetooth: hci4: command 0x0406 tx timeout Bluetooth: hci1: command 0x0406 tx timeout Bluetooth: hci5: command 0x0406 tx timeout INFO: task syz-executor.1:9951 blocked for more than 140 seconds. Not tainted 4.19.208-syzkaller #0 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. syz-executor.1 D28440 9951 8481 0x00000004 Call Trace: context_switch kernel/sched/core.c:2828 [inline] __schedule+0x80c/0x1f70 kernel/sched/core.c:3517 schedule+0x7f/0x1b0 kernel/sched/core.c:3561 __rwsem_down_write_failed_common kernel/locking/rwsem-xadd.c:589 [inline] rwsem_down_write_failed+0x3bb/0x780 kernel/locking/rwsem-xadd.c:618 call_rwsem_down_write_failed+0x17/0x30 arch/x86/lib/rwsem.S:117 __down_write arch/x86/include/asm/rwsem.h:142 [inline] down_write+0x53/0x90 kernel/locking/rwsem.c:72 grab_super+0xaf/0x1f0 fs/super.c:383 sget_userns+0x6e6/0xb70 fs/super.c:511 sget+0xbe/0x100 fs/super.c:570 mount_bdev+0xc9/0x330 fs/super.c:1131 udf_mount+0x10/0x20 fs/udf/super.c:125 mount_fs+0x7f/0x2b0 fs/super.c:1261 vfs_kern_mount.part.11+0x58/0x3d0 fs/namespace.c:961 vfs_kern_mount fs/namespace.c:951 [inline] do_new_mount fs/namespace.c:2492 [inline] do_mount+0x376/0x2630 fs/namespace.c:2822 ksys_mount+0xb1/0xd0 fs/namespace.c:3038 __do_sys_mount fs/namespace.c:3052 [inline] __se_sys_mount fs/namespace.c:3049 [inline] __x64_sys_mount+0xb9/0x150 fs/namespace.c:3049 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x465b09 Code: Bad RIP value. RSP: 002b:00007f0174566188 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5 RAX: ffffffffffffffda RBX: 000000000056c008 RCX: 0000000000465b09 RDX: 0000000020000040 RSI: 0000000020000280 RDI: 00000000200004c0 RBP: 00000000004b069f R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056c008 R13: 00007ffd8061b00f R14: 00007f0174566300 R15: 0000000000022000 Showing all locks held in the system: 1 lock held by khungtaskd/1515: #0: 00000000d6684c52 (rcu_read_lock){....}, at: debug_show_all_locks+0x5b/0x27a kernel/locking/lockdep.c:4443 1 lock held by in:imklog/7807: #0: 00000000ef57f2b4 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0xa7/0xd0 fs/file.c:767 2 locks held by syz-executor.2/9908: 1 lock held by syz-executor.1/9949: 2 locks held by syz-executor.1/9951: #0: 00000000409270c7 (&bdev->bd_fsfreeze_mutex){+.+.}, at: mount_bdev+0x71/0x330 fs/super.c:1125 #1: 000000002562f2dd (&type->s_umount_key#49){+.+.}, at: grab_super+0xaf/0x1f0 fs/super.c:383 ============================================= NMI backtrace for cpu 1 CPU: 1 PID: 1515 Comm: khungtaskd Not tainted 4.19.208-syzkaller #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+0x17c/0x226 lib/dump_stack.c:118 nmi_cpu_backtrace.cold.0+0x3c/0x78 lib/nmi_backtrace.c:101 nmi_trigger_cpumask_backtrace+0xf6/0x120 lib/nmi_backtrace.c:62 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38 trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline] check_hung_uninterruptible_tasks kernel/hung_task.c:203 [inline] watchdog+0x5c3/0xb40 kernel/hung_task.c:287 kthread+0x347/0x410 kernel/kthread.c:259 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415 Sending NMI from CPU 1 to CPUs 0: NMI backtrace for cpu 0 CPU: 0 PID: 92 Comm: kworker/u4:2 Not tainted 4.19.208-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Workqueue: bat_events batadv_nc_worker RIP: 0010:lock_release+0x3f1/0x840 kernel/locking/lockdep.c:3929 Code: 74 01 00 00 65 4c 8b 24 25 c0 df 01 00 49 8d bc 24 84 08 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 0f b6 14 02 <48> 89 f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 92 03 00 00 48 RSP: 0018:ffff8880b52bfbd0 EFLAGS: 00000807 RAX: dffffc0000000000 RBX: 1ffff11016a57f7d RCX: 1ffff11016a5555f RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffff8880b52aab04 RBP: ffff8880b52bfc70 R08: 0000000000000000 R09: ffffed10151643f3 R10: ffffed10151643f3 R11: ffff8880a8b21f9b R12: ffff8880b52aa280 R13: 0000000000000002 R14: ffff8880b52aab00 R15: ffff8880b52aa280 FS: 0000000000000000(0000) GS:ffff8880ba200000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000562abc782728 CR3: 0000000099f2a000 CR4: 00000000003406f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:174 [inline] _raw_spin_unlock_bh+0x1a/0x40 kernel/locking/spinlock.c:200 spin_unlock_bh include/linux/spinlock.h:374 [inline] batadv_nc_purge_paths+0x1c5/0x2c0 net/batman-adv/network-coding.c:482 batadv_nc_worker+0x225/0x630 net/batman-adv/network-coding.c:733 process_one_work+0x7b9/0x15a0 kernel/workqueue.c:2153 worker_thread+0x85/0xb60 kernel/workqueue.c:2296 kthread+0x347/0x410 kernel/kthread.c:259 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415 ---------------- Code disassembly (best guess): 0: 74 01 je 0x3 2: 00 00 add %al,(%rax) 4: 65 4c 8b 24 25 c0 df mov %gs:0x1dfc0,%r12 b: 01 00 d: 49 8d bc 24 84 08 00 lea 0x884(%r12),%rdi 14: 00 15: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax 1c: fc ff df 1f: 48 89 fa mov %rdi,%rdx 22: 48 c1 ea 03 shr $0x3,%rdx 26: 0f b6 14 02 movzbl (%rdx,%rax,1),%edx * 2a: 48 89 f8 mov %rdi,%rax <-- trapping instruction 2d: 83 e0 07 and $0x7,%eax 30: 83 c0 03 add $0x3,%eax 33: 38 d0 cmp %dl,%al 35: 7c 08 jl 0x3f 37: 84 d2 test %dl,%dl 39: 0f 85 92 03 00 00 jne 0x3d1 3f: 48 rex.W