Message-ID: <20200924120609.GS18329@kadam>
Date:   Thu, 24 Sep 2020 15:06:10 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     syzbot <syzbot+f04854e1c5c9e913cc27@...kaller.appspotmail.com>,
        linux-kernel@...r.kernel.org,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        syzkaller-bugs@...glegroups.com
Subject: Re: INFO: rcu detected stall in sys_exit_group (6)


On Thu, Sep 24, 2020 at 07:07:31PM +0800, Hillf Danton wrote:
> 
> Thu, 24 Sep 2020 02:26:25 -0700
> > syzbot found the following issue on:
> > 
> > HEAD commit:    805c6d3c Merge branch 'fixes' of git://git.kernel.org/pub/..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=11fef4e3900000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=af502ec9a451c9fc
> > dashboard link: https://syzkaller.appspot.com/bug?extid=f04854e1c5c9e913cc27
> > compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12d419c5900000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1686b4bb900000
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+f04854e1c5c9e913cc27@...kaller.appspotmail.com
> > 
> > rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
> > rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1):
> > ------------[ cut here ]------------
> > WARNING: CPU: 1 PID: 27130 at kernel/sched/core.c:3013 rq_unlock kernel/sched/sched.h:1325 [inline]
> > WARNING: CPU: 1 PID: 27130 at kernel/sched/core.c:3013 try_invoke_on_locked_down_task+0x12d/0x270 kernel/sched/core.c:3019
> > Kernel panic - not syncing: panic_on_warn set ...
> > CPU: 1 PID: 27130 Comm: syz-executor076 Not tainted 5.9.0-rc6-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > Call Trace:
> >  <IRQ>
> >  __dump_stack lib/dump_stack.c:77 [inline]
> >  dump_stack+0x1d6/0x29e lib/dump_stack.c:118
> >  panic+0x2c0/0x800 kernel/panic.c:231
> >  __warn+0x227/0x250 kernel/panic.c:600
> >  report_bug+0x1b1/0x2e0 lib/bug.c:198
> >  handle_bug+0x42/0x80 arch/x86/kernel/traps.c:234
> >  exc_invalid_op+0x16/0x40 arch/x86/kernel/traps.c:254
> >  asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:536
> > RIP: 0010:try_invoke_on_locked_down_task+0x12d/0x270 kernel/sched/sched.h:1325
> > Code: f8 48 c1 e8 03 42 8a 04 38 84 c0 0f 85 10 01 00 00 8b 74 24 18 48 89 ef e8 90 47 09 00 4c 89 ef e8 48 4c fb 06 e9 a4 00 00 00 <0f> 0b e9 2b ff ff ff 48 c7 c1 34 d6 af 89 80 e1 07 80 c1 03 38 c1
> > RSP: 0018:ffffc90000da8c50 EFLAGS: 00010046
> > RAX: 0000000000000000 RBX: ffff888097326380 RCX: 6195009cdd28a200
> > RDX: ffffc90000da8d00 RSI: ffffffff8162e8d0 RDI: ffff888089c50500
> > RBP: ffffffff8162e8d0 R08: dffffc0000000000 R09: fffffbfff12df8f9
> > R10: fffffbfff12df8f9 R11: 0000000000000000 R12: 0000000000000000
> > R13: ffffffff896ff600 R14: ffff888089c50500 R15: dffffc0000000000
> >  rcu_print_task_stall kernel/rcu/tree_stall.h:267 [inline]
> >  print_other_cpu_stall kernel/rcu/tree_stall.h:475 [inline]
> >  check_cpu_stall kernel/rcu/tree_stall.h:634 [inline]
> >  rcu_pending kernel/rcu/tree.c:3637 [inline]
> >  rcu_sched_clock_irq+0x12bc/0x1eb0 kernel/rcu/tree.c:2519
> >  update_process_times+0x130/0x1b0 kernel/time/timer.c:1710
> >  tick_sched_handle kernel/time/tick-sched.c:176 [inline]
> >  tick_sched_timer+0x25e/0x410 kernel/time/tick-sched.c:1328
> >  __run_hrtimer kernel/time/hrtimer.c:1524 [inline]
> >  __hrtimer_run_queues+0x42d/0x930 kernel/time/hrtimer.c:1588
> >  hrtimer_interrupt+0x373/0xd60 kernel/time/hrtimer.c:1650
> >  local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1080 [inline]
> >  __sysvec_apic_timer_interrupt+0xf0/0x260 arch/x86/kernel/apic/apic.c:1097
> >  asm_call_on_stack+0xf/0x20 arch/x86/entry/entry_64.S:706
> >  </IRQ>
> >  __run_on_irqstack arch/x86/include/asm/irq_stack.h:22 [inline]
> >  run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:48 [inline]
> >  sysvec_apic_timer_interrupt+0x94/0xf0 arch/x86/kernel/apic/apic.c:1091
> >  asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:581
> > RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:770 [inline]
> > RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
> > RIP: 0010:_raw_spin_unlock_irqrestore+0x63/0x90 kernel/locking/spinlock.c:191
> > Code: b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 0c 48 c7 c7 b8 17 6d 89 e8 cc 9b 68 f9 48 83 3d 3c d8 20 01 00 74 2a 4c 89 f7 57 9d <0f> 1f 44 00 00 bf 01 00 00 00 e8 4e a3 04 f9 65 8b 05 73 be b5 77
> > RSP: 0018:ffffc9000ad479a0 EFLAGS: 00000282
> > RAX: 1ffffffff12da2f7 RBX: ffffffff8bc9d3e8 RCX: dffffc0000000000
> > RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000282
> > RBP: 1ffff11010d98d45 R08: ffffffff817ad120 R09: fffffbfff1793a7e
> > R10: fffffbfff1793a7e R11: 0000000000000000 R12: ffff888084aa9000
> > R13: 0000000000000013 R14: 0000000000000282 R15: 0000000000000001
> >  __debug_check_no_obj_freed lib/debugobjects.c:977 [inline]
> >  debug_check_no_obj_freed+0x592/0x640 lib/debugobjects.c:998
> >  free_pages_prepare mm/page_alloc.c:1214 [inline]
> >  free_pcp_prepare+0x1f5/0x400 mm/page_alloc.c:1244
> >  free_unref_page_prepare mm/page_alloc.c:3099 [inline]
> >  free_unref_page_list+0xb0/0x550 mm/page_alloc.c:3168
> >  release_pages+0x13aa/0x1550 mm/swap.c:913
> >  tlb_batch_pages_flush mm/mmu_gather.c:49 [inline]
> >  tlb_flush_mmu_free mm/mmu_gather.c:242 [inline]
> >  tlb_flush_mmu+0x780/0x910 mm/mmu_gather.c:249
> >  tlb_finish_mmu+0xcb/0x200 mm/mmu_gather.c:328
> >  exit_mmap+0x296/0x550 mm/mmap.c:3185
> >  __mmput+0x113/0x370 kernel/fork.c:1076
> >  exit_mm+0x4cd/0x550 kernel/exit.c:483
> >  do_exit+0x576/0x1f20 kernel/exit.c:793
> >  do_group_exit+0x161/0x2d0 kernel/exit.c:903
> >  __do_sys_exit_group+0x13/0x20 kernel/exit.c:914
> >  __se_sys_exit_group+0x10/0x10 kernel/exit.c:912
> >  __x64_sys_exit_group+0x37/0x40 kernel/exit.c:912
> >  do_syscall_64+0x31/0x70 arch/x86/entry/common.c:46
> >  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Hard to understand what the syzbot reported because it's been there after
> 2beaf3280e57 ("sched/core: Add function to sample state of locked-down task").
> Why does it take a couple months to trigger if this is a routine test.

I think this was already fix in linux-next commit 9e097980efe9
("sched/core: Allow try_invoke_on_locked_down_task() with irqs disabled")

regards,
dan carpenter

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