bisecting fixing commit since c98875d930e915d01e8c40c7d3c16f00b3c8abe1 building syzkaller on b0e8efcb4b0aac61f4647a76bbe54a5d38a370ba testing commit c98875d930e915d01e8c40c7d3c16f00b3c8abe1 with gcc (GCC) 8.1.0 kernel signature: 5a7efb39273cb737580e6cbf75aa06b65e30b10acca31f86f658e34d56fd9cce all runs: crashed: INFO: task hung in p9_fd_close testing current HEAD 357668399cf70ccdc0ee8967bff3448d0f4f9ae1 testing commit 357668399cf70ccdc0ee8967bff3448d0f4f9ae1 with gcc (GCC) 8.1.0 kernel signature: 712d65e0c9f956e93131659aa5917fee18041767c14b433819e46ff986238179 all runs: crashed: INFO: task hung in p9_fd_close revisions tested: 2, total time: 31m26.408993435s (build: 17m12.209928312s, test: 13m37.250347691s) the crash still happens on HEAD commit msg: Linux 4.19.103 crash: INFO: task hung in p9_fd_close INFO: task syz-executor.5:22419 blocked for more than 140 seconds. Not tainted 4.19.103-syzkaller #0 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. syz-executor.5 D27912 22419 7086 0x00000004 Call Trace: context_switch kernel/sched/core.c:2826 [inline] __schedule+0x792/0x1c20 kernel/sched/core.c:3515 schedule+0x7f/0x1b0 kernel/sched/core.c:3559 schedule_timeout+0x6d7/0xda0 kernel/time/timer.c:1782 do_wait_for_common kernel/sched/completion.c:83 [inline] __wait_for_common kernel/sched/completion.c:104 [inline] wait_for_common kernel/sched/completion.c:115 [inline] wait_for_completion+0x282/0x460 kernel/sched/completion.c:136 __flush_work+0x3d5/0x7f0 kernel/workqueue.c:2926 __cancel_work_timer+0x2f1/0x430 kernel/workqueue.c:3013 cancel_work_sync+0xb/0x10 kernel/workqueue.c:3049 p9_conn_destroy net/9p/trans_fd.c:878 [inline] p9_fd_close+0x267/0x4e0 net/9p/trans_fd.c:913 p9_client_create+0x8f1/0x10f0 net/9p/client.c:1084 v9fs_session_init+0x1ed/0x14c0 fs/9p/v9fs.c:421 v9fs_mount+0x73/0x770 fs/9p/vfs_super.c:135 mount_fs+0x84/0x2a7 fs/super.c:1261 vfs_kern_mount.part.34+0x58/0x3d0 fs/namespace.c:961 vfs_kern_mount fs/namespace.c:951 [inline] do_new_mount fs/namespace.c:2469 [inline] do_mount+0x36e/0x2410 fs/namespace.c:2799 ksys_mount+0xba/0xe0 fs/namespace.c:3015 __do_sys_mount fs/namespace.c:3029 [inline] __se_sys_mount fs/namespace.c:3026 [inline] __x64_sys_mount+0xb9/0x150 fs/namespace.c:3026 do_syscall_64+0xd6/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x458c29 Code: 08 48 c7 44 24 10 04 00 00 00 e8 62 d8 fa ff 48 8b 44 24 18 48 8b 4c 24 30 48 83 c1 08 48 89 0c 24 48 89 44 24 08 48 c7 44 24 <10> 10 00 00 00 e8 3d d8 fa ff 48 8b 44 24 18 48 89 44 24 40 48 8b RSP: 002b:00007fd5a6e04c78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5 RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000458c29 RDX: 0000000020000100 RSI: 00000000200000c0 RDI: 0000000000000000 RBP: 000000000073bf00 R08: 0000000020000140 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007fd5a6e056d4 R13: 00000000004c4c14 R14: 00000000004d88a0 R15: 00000000ffffffff Showing all locks held in the system: 1 lock held by khungtaskd/1036: #0: 00000000b89906b0 (rcu_read_lock){....}, at: debug_show_all_locks+0x5b/0x27a kernel/locking/lockdep.c:4438 1 lock held by rsyslogd/6842: #0: 000000005d2989bf (&f->f_pos_lock){+.+.}, at: __fdget_pos+0xa7/0xd0 fs/file.c:767 2 locks held by getty/6964: #0: 0000000092f2ef18 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x2d/0x40 drivers/tty/tty_ldsem.c:362 #1: 0000000075ca529c (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x1ee/0x1910 drivers/tty/n_tty.c:2154 2 locks held by getty/6965: #0: 00000000b66899a4 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x2d/0x40 drivers/tty/tty_ldsem.c:362 #1: 0000000006bd1d15 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x1ee/0x1910 drivers/tty/n_tty.c:2154 2 locks held by getty/6966: #0: 000000006cce885c (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x2d/0x40 drivers/tty/tty_ldsem.c:362 #1: 00000000bdf9116b (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x1ee/0x1910 drivers/tty/n_tty.c:2154 2 locks held by getty/6967: #0: 00000000c6163626 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x2d/0x40 drivers/tty/tty_ldsem.c:362 #1: 00000000e723068e (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x1ee/0x1910 drivers/tty/n_tty.c:2154 2 locks held by getty/6968: #0: 0000000055fd32c4 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x2d/0x40 drivers/tty/tty_ldsem.c:362 #1: 00000000395512d9 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x1ee/0x1910 drivers/tty/n_tty.c:2154 2 locks held by getty/6969: #0: 000000003f2c11cf (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x2d/0x40 drivers/tty/tty_ldsem.c:362 #1: 0000000029a20b3b (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x1ee/0x1910 drivers/tty/n_tty.c:2154 2 locks held by getty/6970: #0: 0000000044901c91 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x2d/0x40 drivers/tty/tty_ldsem.c:362 #1: 00000000f62af728 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x1ee/0x1910 drivers/tty/n_tty.c:2154 2 locks held by kworker/0:3/7097: #0: 000000008b438328 ((wq_completion)"events"){+.+.}, at: __write_once_size include/linux/compiler.h:220 [inline] #0: 000000008b438328 ((wq_completion)"events"){+.+.}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline] #0: 000000008b438328 ((wq_completion)"events"){+.+.}, at: atomic64_set include/asm-generic/atomic-instrumented.h:40 [inline] #0: 000000008b438328 ((wq_completion)"events"){+.+.}, at: atomic_long_set include/asm-generic/atomic-long.h:59 [inline] #0: 000000008b438328 ((wq_completion)"events"){+.+.}, at: set_work_data kernel/workqueue.c:617 [inline] #0: 000000008b438328 ((wq_completion)"events"){+.+.}, at: set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline] #0: 000000008b438328 ((wq_completion)"events"){+.+.}, at: process_one_work+0x762/0x1670 kernel/workqueue.c:2124 #1: 000000009fa0be7f ((work_completion)(&m->rq)){+.+.}, at: process_one_work+0x792/0x1670 kernel/workqueue.c:2128 ============================================= NMI backtrace for cpu 1 CPU: 1 PID: 1036 Comm: khungtaskd Not tainted 4.19.103-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+0x123/0x177 lib/dump_stack.c:118 nmi_cpu_backtrace.cold.4+0x3e/0x76 lib/nmi_backtrace.c:101 nmi_trigger_cpumask_backtrace+0xe6/0x11a 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+0x327/0x3f0 kernel/kthread.c:246 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:415 Sending NMI from CPU 1 to CPUs 0: NMI backtrace for cpu 0 CPU: 0 PID: 7 Comm: kworker/u4:0 Not tainted 4.19.103-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_acquire+0x4d1/0x4980 kernel/locking/lockdep.c:3358 Code: 01 c2 41 0f b6 42 21 41 c1 e4 03 83 e2 03 c1 e2 05 83 e0 1f 09 d0 41 89 c5 44 89 c0 41 09 cd 44 89 f9 45 0f b6 7a 22 83 e0 01 <83> e1 03 c1 e0 02 45 88 6a 21 41 83 e7 f8 41 09 cf 41 09 c7 41 83 RSP: 0018:ffff8880aa357a00 EFLAGS: 00000002 RAX: 0000000000000001 RBX: 000000000000069b RCX: 0000000000000000 RDX: 0000000000000000 RSI: 1ffff11015468951 RDI: ffff8880aa344ab4 RBP: ffff8880aa357be8 R08: 0000000000000001 R09: 0000000000000002 R10: ffff8880aa344a90 R11: ffff8880aa344a2c R12: 0000000000000000 R13: 0000000000000006 R14: ffff8880aa3441c0 R15: 0000000000000004 FS: 0000000000000000(0000) GS:ffff8880aea00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffffffffff600400 CR3: 000000008ecc2000 CR4: 00000000001406f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: lock_acquire+0x173/0x3d0 kernel/locking/lockdep.c:3903 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline] _raw_spin_lock_bh+0x31/0x40 kernel/locking/spinlock.c:168 spin_lock_bh include/linux/spinlock.h:334 [inline] batadv_nc_purge_paths+0xc0/0x300 net/batman-adv/network-coding.c:453 batadv_nc_worker+0x1f3/0x630 net/batman-adv/network-coding.c:731 process_one_work+0x835/0x1670 kernel/workqueue.c:2153 worker_thread+0x85/0xb60 kernel/workqueue.c:2296 kthread+0x327/0x3f0 kernel/kthread.c:246 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:415