INFO: task can't die in lock_mount

From: syzbot
Date: Sat Dec 19 2020 - 10:18:27 EST

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Hello,

syzbot found the following issue on:

HEAD commit: 0d52778b Add linux-next specific files for 20201218
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=10b64333500000
kernel config: https://syzkaller.appspot.com/x/.config?x=5c81cc44aa25b5b3
dashboard link: https://syzkaller.appspot.com/bug?extid=88a6c9cb23c5d25506d7
compiler: gcc (GCC) 10.1.0-syz 20200507

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+88a6c9cb23c5d25506d7@xxxxxxxxxxxxxxxxxxxxxxxxx

INFO: task syz-executor.2:16374 can't die for more than 143 seconds.
task:syz-executor.2 state:D stack:27224 pid:16374 ppid: 8541 flags:0x00000004
Call Trace:
context_switch kernel/sched/core.c:4327 [inline]
__schedule+0x8eb/0x21b0 kernel/sched/core.c:5078
schedule+0xcf/0x270 kernel/sched/core.c:5157
rwsem_down_write_slowpath+0x809/0x1220 kernel/locking/rwsem.c:1106
__down_write_common kernel/locking/rwsem.c:1261 [inline]
__down_write_common kernel/locking/rwsem.c:1258 [inline]
__down_write kernel/locking/rwsem.c:1270 [inline]
down_write+0x132/0x150 kernel/locking/rwsem.c:1407
inode_lock include/linux/fs.h:773 [inline]
lock_mount+0x8a/0x2e0 fs/namespace.c:2211
do_new_mount_fc fs/namespace.c:2839 [inline]
do_new_mount fs/namespace.c:2898 [inline]
path_mount+0x1678/0x1e70 fs/namespace.c:3227
do_mount fs/namespace.c:3240 [inline]
__do_sys_mount fs/namespace.c:3448 [inline]
__se_sys_mount fs/namespace.c:3425 [inline]
__x64_sys_mount+0x27f/0x300 fs/namespace.c:3425
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45e149
RSP: 002b:00007f774260fc68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 000000000045e149
RDX: 0000000020002100 RSI: 00000000200020c0 RDI: 0000000000000000
RBP: 000000000119bfd0 R08: 0000000020002140 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000119bf8c
R13: 00007ffe6071fc4f R14: 00007f77426109c0 R15: 000000000119bf8c
INFO: task syz-executor.2:16374 blocked for more than 143 seconds.
Not tainted 5.10.0-next-20201218-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor.2 state:D stack:27224 pid:16374 ppid: 8541 flags:0x00000004
Call Trace:
context_switch kernel/sched/core.c:4327 [inline]
__schedule+0x8eb/0x21b0 kernel/sched/core.c:5078
schedule+0xcf/0x270 kernel/sched/core.c:5157
rwsem_down_write_slowpath+0x809/0x1220 kernel/locking/rwsem.c:1106
__down_write_common kernel/locking/rwsem.c:1261 [inline]
__down_write_common kernel/locking/rwsem.c:1258 [inline]
__down_write kernel/locking/rwsem.c:1270 [inline]
down_write+0x132/0x150 kernel/locking/rwsem.c:1407
inode_lock include/linux/fs.h:773 [inline]
lock_mount+0x8a/0x2e0 fs/namespace.c:2211
do_new_mount_fc fs/namespace.c:2839 [inline]
do_new_mount fs/namespace.c:2898 [inline]
path_mount+0x1678/0x1e70 fs/namespace.c:3227
do_mount fs/namespace.c:3240 [inline]
__do_sys_mount fs/namespace.c:3448 [inline]
__se_sys_mount fs/namespace.c:3425 [inline]
__x64_sys_mount+0x27f/0x300 fs/namespace.c:3425
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45e149
RSP: 002b:00007f774260fc68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 000000000045e149
RDX: 0000000020002100 RSI: 00000000200020c0 RDI: 0000000000000000
RBP: 000000000119bfd0 R08: 0000000020002140 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000119bf8c
R13: 00007ffe6071fc4f R14: 00007f77426109c0 R15: 000000000119bf8c
INFO: task syz-executor.2:16381 can't die for more than 144 seconds.
task:syz-executor.2 state:R running task stack:27912 pid:16381 ppid: 8541 flags:0x00004006
Call Trace:
context_switch kernel/sched/core.c:4327 [inline]
__schedule+0x8eb/0x21b0 kernel/sched/core.c:5078
preempt_schedule_common+0x45/0xc0 kernel/sched/core.c:5238

Showing all locks held in the system:
1 lock held by khungtaskd/1666:
#0: ffffffff8b793ae0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x28c kernel/locking/lockdep.c:6254
1 lock held by in:imklog/8371:
#0: ffff8880213a0d70 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:947
1 lock held by syz-executor.2/16374:
#0: ffff88807e1b9c50 (&type->i_mutex_dir_key#8){++++}-{3:3}, at: inode_lock include/linux/fs.h:773 [inline]
#0: ffff88807e1b9c50 (&type->i_mutex_dir_key#8){++++}-{3:3}, at: lock_mount+0x8a/0x2e0 fs/namespace.c:2211
3 locks held by syz-executor.2/16381:

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 1666 Comm: khungtaskd Not tainted 5.10.0-next-20201218-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x107/0x163 lib/dump_stack.c:120
nmi_cpu_backtrace.cold+0x3c/0xef lib/nmi_backtrace.c:105
nmi_trigger_cpumask_backtrace+0x1b3/0x230 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:147 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:253 [inline]
watchdog+0xe75/0x1020 kernel/hung_task.c:338
kthread+0x3b1/0x4a0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 4528 Comm: kworker/u4:6 Not tainted 5.10.0-next-20201218-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: bat_events batadv_nc_worker
RIP: 0010:check_preemption_disabled+0x2/0x150 lib/smp_processor_id.c:13
Code: 00 00 8b 1d 98 cb 63 04 31 ff 89 de 0f 1f 44 00 00 85 db 75 ae 0f 1f 44 00 00 41 bc 01 00 00 00 e8 d3 a0 a3 fa eb 9f cc 41 56 <41> 55 49 89 f5 41 54 55 48 89 fd 53 0f 1f 44 00 00 65 44 8b 25 25
RSP: 0018:ffffc900092f7b68 EFLAGS: 00000282
RAX: 0000000000000001 RBX: 1ffff9200125ef76 RCX: ffffffff8158f0d8
RDX: 0000000000000001 RSI: ffffffff89bf9f00 RDI: ffffffff89bf9f40
RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff8d7e9bcf
R10: fffffbfff1afd379 R11: 0000000000000000 R12: 0000000000000001
R13: ffffffff8b793ae0 R14: 0000000000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fcc49173000 CR3: 0000000011ffd000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
rcu_lockdep_current_cpu_online kernel/rcu/tree.c:1161 [inline]
rcu_lockdep_current_cpu_online+0x2d/0x150 kernel/rcu/tree.c:1152
rcu_read_lock_held_common kernel/rcu/update.c:110 [inline]
rcu_read_lock_held_common kernel/rcu/update.c:100 [inline]
rcu_read_lock_sched_held+0x25/0x70 kernel/rcu/update.c:121
trace_lock_acquire include/trace/events/lock.h:13 [inline]
lock_acquire+0x5d3/0x750 kernel/locking/lockdep.c:5408
rcu_lock_acquire include/linux/rcupdate.h:259 [inline]
rcu_read_lock include/linux/rcupdate.h:648 [inline]
batadv_nc_purge_orig_hash net/batman-adv/network-coding.c:404 [inline]
batadv_nc_worker+0x12d/0xe80 net/batman-adv/network-coding.c:715
process_one_work+0x98d/0x1630 kernel/workqueue.c:2275
worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
kthread+0x3b1/0x4a0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

---
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