syzbot

INFO: task kworker/u8:6:83 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u8:6    state:D stack:21216 pid:83    tgid:83    ppid:2      task_flags:0x4208060 flags:0x00080000
Workqueue: writeback wb_workfn (flush-7:0)
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x145f/0x5070 kernel/sched/core.c:6863
 __schedule_loop kernel/sched/core.c:6945 [inline]
 rt_mutex_schedule+0x77/0xf0 kernel/sched/core.c:7241
 rt_mutex_slowlock_block kernel/locking/rtmutex.c:1647 [inline]
 __rt_mutex_slowlock kernel/locking/rtmutex.c:1721 [inline]
 __rt_mutex_slowlock_locked+0x1dfe/0x25e0 kernel/locking/rtmutex.c:1760
 rt_mutex_slowlock+0xb5/0x160 kernel/locking/rtmutex.c:1800
 __rt_mutex_lock kernel/locking/rtmutex.c:1815 [inline]
 rwbase_write_lock+0x14f/0x750 kernel/locking/rwbase_rt.c:244
 f2fs_down_write fs/f2fs/f2fs.h:2313 [inline]
 f2fs_balance_fs+0x5b2/0x7d0 fs/f2fs/segment.c:464
 f2fs_write_inode+0x3fb/0x5f0 fs/f2fs/inode.c:826
 write_inode fs/fs-writeback.c:1582 [inline]
 __writeback_single_inode+0x7e4/0x1240 fs/fs-writeback.c:1802
 writeback_sb_inodes+0x8c8/0x1840 fs/fs-writeback.c:2030
 __writeback_inodes_wb+0x111/0x240 fs/fs-writeback.c:2107
 wb_writeback+0x43f/0xaa0 fs/fs-writeback.c:2218
 wb_check_old_data_flush fs/fs-writeback.c:2322 [inline]
 wb_do_writeback fs/fs-writeback.c:2375 [inline]
 wb_workfn+0xad7/0xee0 fs/fs-writeback.c:2403
 process_one_work kernel/workqueue.c:3257 [inline]
 process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>

Showing all locks held in the system:
4 locks held by rcuc/0/20:
3 locks held by rcuc/1/28:
1 lock held by khungtaskd/38:
 #0: ffffffff8d5ae940 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #0: ffffffff8d5ae940 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
 #0: ffffffff8d5ae940 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6775
4 locks held by kworker/u8:4/59:
 #0: ffff88801ce9b938 ((wq_completion)writeback){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3232 [inline]
 #0: ffff88801ce9b938 ((wq_completion)writeback){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x1770 kernel/workqueue.c:3340
 #1: ffffc9000125fbc0 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3233 [inline]
 #1: ffffc9000125fbc0 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x1770 kernel/workqueue.c:3340
 #2: ffff8880579cc0d0 (&type->s_umount_key#55){++++}-{4:4}, at: super_trylock_shared+0x20/0xf0 fs/super.c:563
 #3: ffff888020ad5a80 (&sbi->gc_lock){+.+.}-{4:4}, at: f2fs_down_write fs/f2fs/f2fs.h:2313 [inline]
 #3: ffff888020ad5a80 (&sbi->gc_lock){+.+.}-{4:4}, at: f2fs_balance_fs+0x5b2/0x7d0 fs/f2fs/segment.c:464
4 locks held by kworker/u8:6/83:
 #0: ffff88801ce9b938 ((wq_completion)writeback){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3232 [inline]
 #0: ffff88801ce9b938 ((wq_completion)writeback){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x1770 kernel/workqueue.c:3340
 #1: ffffc9000154fbc0 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3233 [inline]
 #1: ffffc9000154fbc0 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x1770 kernel/workqueue.c:3340
 #2: ffff88803d7c60d0 (&type->s_umount_key#55){++++}-{4:4}, at: super_trylock_shared+0x20/0xf0 fs/super.c:563
 #3: ffff888023e99a80 (&sbi->gc_lock){+.+.}-{4:4}, at: f2fs_down_write fs/f2fs/f2fs.h:2313 [inline]
 #3: ffff888023e99a80 (&sbi->gc_lock){+.+.}-{4:4}, at: f2fs_balance_fs+0x5b2/0x7d0 fs/f2fs/segment.c:464
4 locks held by kworker/u8:14/3451:
 #0: ffff88801ce9b938 ((wq_completion)writeback){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3232 [inline]
 #0: ffff88801ce9b938 ((wq_completion)writeback){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x1770 kernel/workqueue.c:3340
 #1: ffffc9000c8efbc0 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3233 [inline]
 #1: ffffc9000c8efbc0 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x1770 kernel/workqueue.c:3340
 #2: ffff888030a880d0 (&type->s_umount_key#55){++++}-{4:4}, at: super_trylock_shared+0x20/0xf0 fs/super.c:563
 #3: ffff88802a641a80 (&sbi->gc_lock){+.+.}-{4:4}, at: f2fs_down_write fs/f2fs/f2fs.h:2313 [inline]
 #3: ffff88802a641a80 (&sbi->gc_lock){+.+.}-{4:4}, at: f2fs_balance_fs+0x5b2/0x7d0 fs/f2fs/segment.c:464
2 locks held by getty/5558:
 #0: ffff88814e8af0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc90003e7e2e0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x44f/0x1460 drivers/tty/n_tty.c:2211
4 locks held by syz.0.17/5963:
6 locks held by syz.1.54/6329:
6 locks held by syz.2.56/6368:
3 locks held by syz.3.72/6542:

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

NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 38 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x274/0x2d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x17a/0x300 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
 __sys_info lib/sys_info.c:157 [inline]
 sys_info+0x135/0x170 lib/sys_info.c:165
 check_hung_uninterruptible_tasks kernel/hung_task.c:346 [inline]
 watchdog+0xf95/0xfe0 kernel/hung_task.c:515
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 6368 Comm: syz.2.56 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:__lock_acquire+0x3e/0x2cf0 kernel/locking/lockdep.c:-1
Code: 05 77 8e 16 10 48 89 84 24 e0 00 00 00 65 48 8b 04 25 08 10 b3 91 48 89 44 24 08 31 ed 83 3d a8 c4 3e 0d 00 0f 84 ef 13 00 00 <45> 89 cf 49 89 f9 48 8b 07 48 3d a0 b3 76 92 0f 84 da 13 00 00 41
RSP: 0018:ffffc900057d69a8 EFLAGS: 00000002
RAX: ffff88801b785ac0 RBX: 0000000000000000 RCX: 0000000000000002
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff8d5ae940
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: ffff88802ca19b78 R11: ffffed1005943373 R12: 0000000000000002
R13: ffffffff8d5ae940 R14: 0000000000000000 R15: 0000000000000246
FS:  00007fc4d6a0e6c0(0000) GS:ffff888126def000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f5856337005 CR3: 000000001b7fc000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 lock_acquire+0x107/0x340 kernel/locking/lockdep.c:5868
 rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 rcu_read_lock include/linux/rcupdate.h:867 [inline]
 percpu_ref_tryget_many include/linux/percpu-refcount.h:241 [inline]
 percpu_ref_tryget include/linux/percpu-refcount.h:266 [inline]
 blkg_tryget+0x3c/0x250 block/blk-cgroup.h:329
 blkg_tryget_closest block/blk-cgroup.c:2098 [inline]
 bio_associate_blkg_from_css+0xa8e/0xcf0 block/blk-cgroup.c:2130
 bio_associate_blkg+0x170/0x230 block/blk-cgroup.c:2161
 bio_init block/bio.c:267 [inline]
 bio_init_inline include/linux/bio.h:413 [inline]
 bio_alloc_bioset+0x5bd/0x14f0 block/bio.c:587
 f2fs_grab_read_bio+0x23d/0x720 fs/f2fs/data.c:1050
 f2fs_submit_page_read+0x9a/0x100 fs/f2fs/data.c:1093
 f2fs_get_read_data_folio+0x4ae/0x7b0 fs/f2fs/data.c:1261
 f2fs_get_lock_data_folio+0x54/0x1f0 fs/f2fs/data.c:1310
 move_data_page fs/f2fs/gc.c:1466 [inline]
 gc_data_segment fs/f2fs/gc.c:1690 [inline]
 do_garbage_collect+0x34db/0x6f80 fs/f2fs/gc.c:1858
 f2fs_gc+0xcb0/0x2530 fs/f2fs/gc.c:1965
 f2fs_balance_fs+0x5fe/0x7d0 fs/f2fs/segment.c:466
 f2fs_map_blocks+0x3449/0x40b0 fs/f2fs/data.c:1789
 f2fs_expand_inode_data+0x631/0xa70 fs/f2fs/file.c:1934
 f2fs_fallocate+0x4e8/0x970 fs/f2fs/file.c:2037
 vfs_fallocate+0x672/0x7f0 fs/open.c:339
 ksys_fallocate fs/open.c:363 [inline]
 __do_sys_fallocate fs/open.c:368 [inline]
 __se_sys_fallocate fs/open.c:366 [inline]
 __x64_sys_fallocate+0xc0/0x110 fs/open.c:366
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc4d739f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fc4d6a0e038 EFLAGS: 00000246 ORIG_RAX: 000000000000011d
RAX: ffffffffffffffda RBX: 00007fc4d75f5fa0 RCX: 00007fc4d739f749
RDX: 0000000000000008 RSI: 0000000000000001 RDI: 0000000000000006
RBP: 00007fc4d7423f91 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000001101f0 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc4d75f6038 R14: 00007fc4d75f5fa0 R15: 00007fff1e2a1298
 </TASK>