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Date:   Sat, 18 Dec 2021 21:22:57 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     syzbot <syzbot+9c3fb12e9128b6e1d7eb@...kaller.appspotmail.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: Re: [syzbot] INFO: task hung in jbd2_journal_commit_transaction (3)

On Sat, Dec 18, 2021 at 11:50:20AM -0800, syzbot wrote:
> INFO: task jbd2/sda1-8:2937 blocked for more than 143 seconds.
>       Not tainted 5.16.0-rc5-syzkaller #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

sched_setattr(0x0, &(0x7f0000000080)={0x38, 0x1, 0x0, 0x0, 0x1}, 0x0)

so you've set a SCHED_FIFO priority and then are surprised that some
tasks are getting starved?

> task:jbd2/sda1-8     state:D stack:27112 pid: 2937 ppid:     2 flags:0x00004000
> Call Trace:
>  <TASK>
>  context_switch kernel/sched/core.c:4972 [inline]
>  __schedule+0xa9a/0x4940 kernel/sched/core.c:6253
>  schedule+0xd2/0x260 kernel/sched/core.c:6326
>  io_schedule+0xee/0x170 kernel/sched/core.c:8371
>  bit_wait_io+0x12/0xd0 kernel/sched/wait_bit.c:209
>  __wait_on_bit+0x60/0x190 kernel/sched/wait_bit.c:49
>  out_of_line_wait_on_bit+0xd5/0x110 kernel/sched/wait_bit.c:64
>  wait_on_bit_io include/linux/wait_bit.h:101 [inline]
>  __wait_on_buffer+0x7a/0x90 fs/buffer.c:122
>  wait_on_buffer include/linux/buffer_head.h:356 [inline]
>  journal_wait_on_commit_record fs/jbd2/commit.c:175 [inline]
>  jbd2_journal_commit_transaction+0x4e3c/0x6be0 fs/jbd2/commit.c:931
>  kjournald2+0x1d0/0x930 fs/jbd2/journal.c:213
>  kthread+0x405/0x4f0 kernel/kthread.c:327
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
>  </TASK>
> 
> Showing all locks held in the system:
> 1 lock held by khungtaskd/27:
>  #0: ffffffff8bb812e0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:6458
> 1 lock held by udevd/2974:
> 2 locks held by getty/3287:
>  #0: ffff88807ec56098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:252
>  #1: ffffc90002b8e2e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0xcf0/0x1230 drivers/tty/n_tty.c:2113
> 2 locks held by kworker/1:0/3663:
>  #0: ffff888010c76538 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
>  #0: ffff888010c76538 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: arch_atomic_long_set include/linux/atomic/atomic-long.h:41 [inline]
>  #0: ffff888010c76538 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: atomic_long_set include/linux/atomic/atomic-instrumented.h:1198 [inline]
>  #0: ffff888010c76538 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:635 [inline]
>  #0: ffff888010c76538 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:662 [inline]
>  #0: ffff888010c76538 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: process_one_work+0x896/0x1690 kernel/workqueue.c:2269
>  #1: ffffc90001b27db0 ((work_completion)(&rew.rew_work)){+.+.}-{0:0}, at: process_one_work+0x8ca/0x1690 kernel/workqueue.c:2273
> 2 locks held by syz-executor.2/13278:
>  #0: ffffffff8bc4c6c8 (perf_sched_mutex){+.+.}-{3:3}, at: account_event kernel/events/core.c:11445 [inline]
>  #0: ffffffff8bc4c6c8 (perf_sched_mutex){+.+.}-{3:3}, at: perf_event_alloc.part.0+0x31f9/0x3b10 kernel/events/core.c:11678
>  #1: ffffffff8bb8a668 (rcu_state.exp_mutex){+.+.}-{3:3}, at: exp_funnel_lock kernel/rcu/tree_exp.h:290 [inline]
>  #1: ffffffff8bb8a668 (rcu_state.exp_mutex){+.+.}-{3:3}, at: synchronize_rcu_expedited+0x4fa/0x620 kernel/rcu/tree_exp.h:836
> 
> =============================================
> 
> NMI backtrace for cpu 0
> CPU: 0 PID: 27 Comm: khungtaskd Not tainted 5.16.0-rc5-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
>  nmi_cpu_backtrace.cold+0x47/0x144 lib/nmi_backtrace.c:111
>  nmi_trigger_cpumask_backtrace+0x1b3/0x230 lib/nmi_backtrace.c:62
>  trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
>  check_hung_uninterruptible_tasks kernel/hung_task.c:210 [inline]
>  watchdog+0xc1d/0xf50 kernel/hung_task.c:295
>  kthread+0x405/0x4f0 kernel/kthread.c:327
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
>  </TASK>
> Sending NMI from CPU 0 to CPUs 1:
> NMI backtrace for cpu 1
> CPU: 1 PID: 10 Comm: kworker/u4:1 Not tainted 5.16.0-rc5-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: events_unbound toggle_allocation_gate
> RIP: 0010:__kasan_check_read+0x4/0x10 mm/kasan/shadow.c:31
> Code: 44 07 48 85 db 0f 85 d0 9f 45 07 48 83 c4 60 5b 5d 41 5c 41 5d c3 c3 e9 d0 a0 45 07 cc cc cc cc cc cc cc cc cc cc 48 8b 0c 24 <89> f6 31 d2 e9 f3 f9 ff ff 0f 1f 00 48 8b 0c 24 89 f6 ba 01 00 00
> RSP: 0018:ffffc90000f0f630 EFLAGS: 00000002
> RAX: 0000000000000002 RBX: 1ffff920001e1ece RCX: ffffffff815b774f
> RDX: 0000000000000092 RSI: 0000000000000008 RDI: ffffffff8ff77a10
> RBP: 0000000000000100 R08: 0000000000000000 R09: ffffffff8ff77a17
> R10: 0000000000000001 R11: 000000000000003f R12: 0000000000000008
> R13: ffff888011c7eda8 R14: 0000000000000092 R15: ffff888011c7edc8
> FS:  0000000000000000(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005555557b2708 CR3: 000000000b88e000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  instrument_atomic_read include/linux/instrumented.h:71 [inline]
>  test_bit include/asm-generic/bitops/instrumented-non-atomic.h:134 [inline]
>  hlock_class kernel/locking/lockdep.c:199 [inline]
>  mark_lock+0xef/0x17b0 kernel/locking/lockdep.c:4583
>  mark_usage kernel/locking/lockdep.c:4526 [inline]
>  __lock_acquire+0x8a7/0x54a0 kernel/locking/lockdep.c:4981
>  lock_acquire kernel/locking/lockdep.c:5637 [inline]
>  lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5602
>  __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
>  _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:154
>  spin_lock include/linux/spinlock.h:349 [inline]
>  __get_locked_pte+0x2b6/0x4d0 mm/memory.c:1722
>  get_locked_pte include/linux/mm.h:2160 [inline]
>  __text_poke+0x1ae/0x8c0 arch/x86/kernel/alternative.c:1000
>  text_poke_bp_batch+0x3d7/0x560 arch/x86/kernel/alternative.c:1361
>  text_poke_flush arch/x86/kernel/alternative.c:1451 [inline]
>  text_poke_flush arch/x86/kernel/alternative.c:1448 [inline]
>  text_poke_finish+0x16/0x30 arch/x86/kernel/alternative.c:1458
>  arch_jump_label_transform_apply+0x13/0x20 arch/x86/kernel/jump_label.c:146
>  jump_label_update+0x1d5/0x430 kernel/jump_label.c:830
>  static_key_enable_cpuslocked+0x1b1/0x260 kernel/jump_label.c:177
>  static_key_enable+0x16/0x20 kernel/jump_label.c:190
>  toggle_allocation_gate mm/kfence/core.c:732 [inline]
>  toggle_allocation_gate+0x100/0x390 mm/kfence/core.c:724
>  process_one_work+0x9b2/0x1690 kernel/workqueue.c:2298
>  worker_thread+0x658/0x11f0 kernel/workqueue.c:2445
>  kthread+0x405/0x4f0 kernel/kthread.c:327
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
>  </TASK>
> sd 0:0:1:0: tag#6693 FAILED Result: hostbyte=DID_ABORT driverbyte=DRIVER_OK cmd_age=0s
> sd 0:0:1:0: tag#6693 CDB: opcode=0xe5 (vendor)
> sd 0:0:1:0: tag#6693 CDB[00]: e5 f4 32 73 2f 4e 09 6d 26 e2 c7 35 d1 35 12 1c
> sd 0:0:1:0: tag#6693 CDB[10]: 92 1b da 40 b8 58 5b a8 d4 7d 34 f3 90 4c f1 2d
> sd 0:0:1:0: tag#6693 CDB[20]: ba
> ----------------
> Code disassembly (best guess):
>    0:	44 07                	rex.R (bad)
>    2:	48 85 db             	test   %rbx,%rbx
>    5:	0f 85 d0 9f 45 07    	jne    0x7459fdb
>    b:	48 83 c4 60          	add    $0x60,%rsp
>    f:	5b                   	pop    %rbx
>   10:	5d                   	pop    %rbp
>   11:	41 5c                	pop    %r12
>   13:	41 5d                	pop    %r13
>   15:	c3                   	retq
>   16:	c3                   	retq
>   17:	e9 d0 a0 45 07       	jmpq   0x745a0ec
>   1c:	cc                   	int3
>   1d:	cc                   	int3
>   1e:	cc                   	int3
>   1f:	cc                   	int3
>   20:	cc                   	int3
>   21:	cc                   	int3
>   22:	cc                   	int3
>   23:	cc                   	int3
>   24:	cc                   	int3
>   25:	cc                   	int3
>   26:	48 8b 0c 24          	mov    (%rsp),%rcx
> * 2a:	89 f6                	mov    %esi,%esi <-- trapping instruction
>   2c:	31 d2                	xor    %edx,%edx
>   2e:	e9 f3 f9 ff ff       	jmpq   0xfffffa26
>   33:	0f 1f 00             	nopl   (%rax)
>   36:	48 8b 0c 24          	mov    (%rsp),%rcx
>   3a:	89 f6                	mov    %esi,%esi
>   3c:	ba                   	.byte 0xba
>   3d:	01 00                	add    %eax,(%rax)
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches

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