Re: [syzbot] [fs?] INFO: rcu detected stall in sys_close (5)

[Eric Dumazet]

On 8/29/23 10:53, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    727dbda16b83 Merge tag 'hardening-v6.6-rc1' of git://git.k..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=158c0cdba80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=45047a5b8c295201
> dashboard link: https://syzkaller.appspot.com/bug?extid=e46fbd5289363464bc13
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14780797a80000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17c1fc9fa80000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/3b19428c542a/disk-727dbda1.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/45ed4d6b4633/vmlinux-727dbda1.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/4c3abf020089/bzImage-727dbda1.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+e46fbd5289363464bc13@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 0-.... } 2663 jiffies s: 873 root: 0x1/.
> rcu: blocking rcu_node structures (internal RCU debug):
> Sending NMI from CPU 1 to CPUs 0:
> NMI backtrace for cpu 0
> CPU: 0 PID: 5177 Comm: syz-executor273 Not tainted 6.5.0-syzkaller-00453-g727dbda16b83 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023
> RIP: 0010:check_kcov_mode kernel/kcov.c:173 [inline]
> RIP: 0010:write_comp_data+0x21/0x90 kernel/kcov.c:236
> Code: 2e 0f 1f 84 00 00 00 00 00 65 8b 05 01 b2 7d 7e 49 89 f1 89 c6 49 89 d2 81 e6 00 01 00 00 49 89 f8 65 48 8b 14 25 80 b9 03 00 <a9> 00 01 ff 00 74 0e 85 f6 74 59 8b 82 04 16 00 00 85 c0 74 4f 8b
> RSP: 0018:ffffc90000007bb8 EFLAGS: 00000206
> RAX: 0000000000000101 RBX: ffffc9000dc0d140 RCX: ffffffff885893b0
> RDX: ffff88807c075940 RSI: 0000000000000100 RDI: 0000000000000001
> RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: ffffc9000dc0d178
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> FS:  0000555555d54380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f6b442f6130 CR3: 000000006fe1c000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   <NMI>
>   </NMI>
>   <IRQ>
>   pie_calculate_probability+0x480/0x850 net/sched/sch_pie.c:415
>   fq_pie_timer+0x1da/0x4f0 net/sched/sch_fq_pie.c:387
>   call_timer_fn+0x1a0/0x580 kernel/time/timer.c:1700
>   expire_timers kernel/time/timer.c:1751 [inline]
>   __run_timers+0x764/0xb10 kernel/time/timer.c:2022
>   run_timer_softirq+0x58/0xd0 kernel/time/timer.c:2035
>   __do_softirq+0x218/0x965 kernel/softirq.c:553
>   invoke_softirq kernel/softirq.c:427 [inline]
>   __irq_exit_rcu kernel/softirq.c:632 [inline]
>   irq_exit_rcu+0xb7/0x120 kernel/softirq.c:644
>   sysvec_apic_timer_interrupt+0x93/0xc0 arch/x86/kernel/apic/apic.c:1109
>   </IRQ>
>   <TASK>
>   asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:645
> RIP: 0010:__x64_sys_close+0x0/0xf0 fs/open.c:1557
> Code: 1a 48 83 ec 80 5b 5d 41 5c c3 e8 eb bb f1 ff e9 73 ff ff ff e8 e1 bb f1 ff eb 8b e8 2a 06 4a 08 66 2e 0f 1f 84 00 00 00 00 00 <f3> 0f 1e fa 55 53 48 89 fb e8 c2 81 9d ff 48 8d 7b 70 48 b8 00 00
> RSP: 0018:ffffc9000459ff38 EFLAGS: 00000206
> RAX: 0000000000000003 RBX: ffffc9000459ff58 RCX: 1ffffffff1d56e59
> RDX: ffffffffffffffff RSI: 0000000000000000 RDI: ffffc9000459ff58
> RBP: ffffc9000459ff48 R08: 0000000000000001 R09: 0000000000000001
> R10: ffffffff8eaba457 R11: 0000000000000000 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>   do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f6b4427b290
> Code: ff f7 d8 64 89 02 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 80 3d f1 8d 07 00 00 74 17 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 48 c3 0f 1f 80 00 00 00 00 48 83 ec 18 89 7c
> RSP: 002b:00007ffd4ca6aa18 EFLAGS: 00000202 ORIG_RAX: 0000000000000003
> RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 00007f6b4427b290
> RDX: 0000000000000000 RSI: 00000000200007c0 RDI: 0000000000000005
> RBP: 00000000000f4240 R08: 0000000055d55610 R09: 0000000055d55610
> R10: 0000000000000000 R11: 0000000000000202 R12: 00000000000220c3
> R13: 00007ffd4ca6aa24 R14: 00007ffd4ca6aa40 R15: 00007ffd4ca6aa30
>   </TASK>
> INFO: NMI handler (nmi_cpu_backtrace_handler) took too long to run: 1.831 msecs
>
>
> ---
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> If the bug is already fixed, let syzbot know by replying with:
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>
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#syz set subsystems: net

fq_pie_timer() should not attempt to loop over up to 65536 flows,
this takes up to 5 ms on ASAN builds.

> If the bug is a duplicate of another bug, reply with:
> #syz dup: exact-subject-of-another-report
>
> If you want to undo deduplication, reply with:
> #syz undup