Date: Fri, 1 Dec 2023 20:48:54 +0100
From: Eric Dumazet <eric.dumazet@...il.com>
To: Vinicius Costa Gomes <vinicius.gomes@...el.com>,
 Jamal Hadi Salim <jhs@...atatu.com>
Cc: Vladimir Oltean <vladimir.oltean@....com>,
 Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>,
 Jakub Kicinski <kuba@...nel.org>,
 Linux Kernel Network Developers <netdev@...r.kernel.org>, edumazet@...gle.com
Subject: Re: Fwd: [syzbot] [net?] INFO: rcu detected stall in sys_socket (10)


On 12/1/23 01:12, Vinicius Costa Gomes wrote:
> Jamal Hadi Salim <jhs@...atatu.com> writes:
>
>> Vinicius/Vladmir,
>> I pinged you on this already. Can you take a look please? There is a
>> reproducer..
>>
> It seems to be another one of those, syzkaller managed to produce a
> schedule with a small enough interval that it's going to starve some
> other things. (in this case, the interval is 127 ns)
>
> We already reject intervals that won't allow the passage of the smallest
> ethernet packet. I am running out of ideas that we could do to, at least
> at configuration time.
>
> But one almost crazy idea turned up: what if we only start the timer
> when there are actually packets in the qdisc? i.e. if the queue was
> empty, we would only start the timer during "empty -> non-empty"
> enqueue(), and stop the timer when the queue goes back to empty.
>
> I think that way, we remove the issue that causes most of the syzkaller
> reports, and we would reduce the CPU overhead when taprio is idle (on a
> non-debug system with the problematic schedule I am seeing ~2% overhead
> in perf top).
>
> Does that sound like it could work?

It seems this is a periodic timer with a fix value ?

And a packet can sit in taprio for a long time if skb->tstamp is far away,

you can be sure syzbot will know how to feed such delayed packets.

It is unclear why a short timer is reset regardless of what progress can 
be done during this period.

net/sched/sch_fq.c only arms a timer based on the earliest time we can 
make forward progress.

This taprio bug is causing many syzbot reports, with different signatures.

Thanks.



>
>> cheers,
>> jamal
>>
>> ---------- Forwarded message ---------
>> From: syzbot <syzbot+de8e83db70e8beedd556@...kaller.appspotmail.com>
>> Date: Thu, Nov 30, 2023 at 10:24 AM
>> Subject: [syzbot] [net?] INFO: rcu detected stall in sys_socket (10)
>> To: <bp@...en8.de>, <davem@...emloft.net>, <edumazet@...gle.com>,
>> <hpa@...or.com>, <jhs@...atatu.com>, <jiri@...nulli.us>,
>> <kuba@...nel.org>, <linux-kernel@...r.kernel.org>, <mingo@...hat.com>,
>> <netdev@...r.kernel.org>, <pabeni@...hat.com>,
>> <syzkaller-bugs@...glegroups.com>, <tglx@...utronix.de>,
>> <vinicius.gomes@...el.com>, <willemdebruijn.kernel@...il.com>,
>> <x86@...nel.org>, <xiyou.wangcong@...il.com>
>>
>>
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit:    18d46e76d7c2 Merge tag 'for-6.7-rc3-tag' of git://git.kern..
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=16bcc8b4e80000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=bb39fe85d254f638
>> dashboard link: https://syzkaller.appspot.com/bug?extid=de8e83db70e8beedd556
>> 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=12172952e80000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1086b58ae80000
>>
>> Downloadable assets:
>> disk image: https://storage.googleapis.com/syzbot-assets/0ce5608c89e8/disk-18d46e76.raw.xz
>> vmlinux: https://storage.googleapis.com/syzbot-assets/eef847faba9c/vmlinux-18d46e76.xz
>> kernel image: https://storage.googleapis.com/syzbot-assets/6a3df3288860/bzImage-18d46e76.xz
>>
>> The issue was bisected to:
>>
>> commit 5a781ccbd19e4664babcbe4b4ead7aa2b9283d22
>> Author: Vinicius Costa Gomes <vinicius.gomes@...el.com>
>> Date:   Sat Sep 29 00:59:43 2018 +0000
>>
>>      tc: Add support for configuring the taprio scheduler
>>
>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=16a29b52e80000
>> final oops:     https://syzkaller.appspot.com/x/report.txt?x=15a29b52e80000
>> console output: https://syzkaller.appspot.com/x/log.txt?x=11a29b52e80000
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+de8e83db70e8beedd556@...kaller.appspotmail.com
>> Fixes: 5a781ccbd19e ("tc: Add support for configuring the taprio scheduler")
>>
>> rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
>> rcu:    0-...!: (1 GPs behind) idle=79f4/1/0x4000000000000000
>> softirq=5546/5548 fqs=1
>> rcu:    (detected by 1, t=10503 jiffies, g=5017, q=384 ncpus=2)
>> Sending NMI from CPU 1 to CPUs 0:
>> NMI backtrace for cpu 0
>> CPU: 0 PID: 5106 Comm: syz-executor201 Not tainted
>> 6.7.0-rc3-syzkaller-00024-g18d46e76d7c2 #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine,
>> BIOS Google 11/10/2023
>> RIP: 0010:__run_hrtimer kernel/time/hrtimer.c:1686 [inline]
>> RIP: 0010:__hrtimer_run_queues+0x62e/0xc20 kernel/time/hrtimer.c:1752
>> Code: fc ff df 48 89 fa 48 c1 ea 03 0f b6 04 02 48 89 fa 83 e2 07 38
>> d0 7f 08 84 c0 0f 85 fb 04 00 00 45 0f b6 6e 3b 31 ff 44 89 ee <e8> 2d
>> 46 11 00 45 84 ed 0f 84 8e fb ff ff e8 ef 4a 11 00 4c 89 f7
>> RSP: 0018:ffffc90000007e40 EFLAGS: 00000046
>> RAX: 0000000000000000 RBX: ffff8880b982ba40 RCX: ffffffff817642f9
>> RDX: 0000000000000003 RSI: 0000000000000000 RDI: 0000000000000000
>> RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000000
>> R10: 0000000000000001 R11: 0000000000000002 R12: ffff8880b982b940
>> R13: 0000000000000000 R14: ffff88801c43a340 R15: ffffffff88a2daf0
>> FS:  00005555566fe380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007fe9404c73b0 CR3: 0000000076e2d000 CR4: 0000000000350ef0
>> Call Trace:
>>   <NMI>
>>   </NMI>
>>   <IRQ>
>>   hrtimer_interrupt+0x31b/0x800 kernel/time/hrtimer.c:1814
>>   local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1065 [inline]
>>   __sysvec_apic_timer_interrupt+0x105/0x400 arch/x86/kernel/apic/apic.c:1082
>>   sysvec_apic_timer_interrupt+0x90/0xb0 arch/x86/kernel/apic/apic.c:1076
>>   </IRQ>
>>   <TASK>
>>   asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:645
>> RIP: 0010:lock_acquire+0x1ef/0x520 kernel/locking/lockdep.c:5722
>> Code: c1 05 bd 6c 9a 7e 83 f8 01 0f 85 b4 02 00 00 9c 58 f6 c4 02 0f
>> 85 9f 02 00 00 48 85 ed 74 01 fb 48 b8 00 00 00 00 00 fc ff df <48> 01
>> c3 48 c7 03 00 00 00 00 48 c7 43 08 00 00 00 00 48 8b 84 24
>> RSP: 0018:ffffc9000432fb00 EFLAGS: 00000206
>> RAX: dffffc0000000000 RBX: 1ffff92000865f62 RCX: ffffffff81672c0e
>> RDX: 0000000000000001 RSI: ffffffff8accbae0 RDI: ffffffff8b2f0dc0
>> RBP: 0000000000000200 R08: 0000000000000000 R09: fffffbfff23e33d0
>> R10: ffffffff91f19e87 R11: 0000000000000000 R12: 0000000000000001
>> R13: 0000000000000000 R14: ffffffff8d0f0b48 R15: 0000000000000000
>>   __mutex_lock_common kernel/locking/mutex.c:603 [inline]
>>   __mutex_lock+0x175/0x9d0 kernel/locking/mutex.c:747
>>   pcpu_alloc+0xbb8/0x1420 mm/percpu.c:1769
>>   packet_alloc_pending net/packet/af_packet.c:1232 [inline]
>>   packet_create+0x2b7/0x8e0 net/packet/af_packet.c:3373
>>   __sock_create+0x328/0x800 net/socket.c:1569
>>   sock_create net/socket.c:1620 [inline]
>>   __sys_socket_create net/socket.c:1657 [inline]
>>   __sys_socket+0x14c/0x260 net/socket.c:1704
>>   __do_sys_socket net/socket.c:1718 [inline]
>>   __se_sys_socket net/socket.c:1716 [inline]
>>   __x64_sys_socket+0x72/0xb0 net/socket.c:1716
>>   do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>>   do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
>>   entry_SYSCALL_64_after_hwframe+0x63/0x6b
>> RIP: 0033:0x7fe940479de9
>> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 d1 19 00 00 90 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 b8 ff ff ff f7 d8 64 89 01 48
>> RSP: 002b:00007ffe1bf080b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000029
>> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fe940479de9
>> RDX: 0000000000000000 RSI: 0000000800000003 RDI: 0000000000000011
>> RBP: 00000000000f4240 R08: 0000000000000000 R09: 0000000100000000
>> R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffe1bf08110
>> R13: 0000000000030c67 R14: 00007ffe1bf080dc R15: 0000000000000003
>>   </TASK>
>> INFO: NMI handler (nmi_cpu_backtrace_handler) took too long to run: 1.067 msecs
>> rcu: rcu_preempt kthread timer wakeup didn't happen for 10497 jiffies!
>> g5017 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
>> rcu:    Possible timer handling issue on cpu=0 timer-softirq=2416
>> rcu: rcu_preempt kthread starved for 10498 jiffies! g5017 f0x0
>> RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=0
>> rcu:    Unless rcu_preempt kthread gets sufficient CPU time, OOM is
>> now expected behavior.
>> rcu: RCU grace-period kthread stack dump:
>> task:rcu_preempt     state:I stack:27904 pid:17    tgid:17    ppid:2
>>     flags:0x00004000
>> Call Trace:
>>   <TASK>
>>   context_switch kernel/sched/core.c:5376 [inline]
>>   __schedule+0xedb/0x5af0 kernel/sched/core.c:6688
>>   __schedule_loop kernel/sched/core.c:6763 [inline]
>>   schedule+0xe9/0x270 kernel/sched/core.c:6778
>>   schedule_timeout+0x137/0x290 kernel/time/timer.c:2167
>>   rcu_gp_fqs_loop+0x1ec/0xb10 kernel/rcu/tree.c:1631
>>   rcu_gp_kthread+0x24b/0x380 kernel/rcu/tree.c:1830
>>   kthread+0x2c6/0x3a0 kernel/kthread.c:388
>>   ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
>>   ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
>>   </TASK>
>>
>>
>> ---
>> 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.
>> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
>>
>> If the report is already addressed, let syzbot know by replying with:
>> #syz fix: exact-commit-title
>>
>> If you want syzbot to run the reproducer, reply with:
>> #syz test: git://repo/address.git branch-or-commit-hash
>> If you attach or paste a git patch, syzbot will apply it before testing.
>>
>> If you want to overwrite report's subsystems, reply with:
>> #syz set subsystems: new-subsystem
>> (See the list of subsystem names on the web dashboard)
>>
>> If the report is a duplicate of another one, reply with:
>> #syz dup: exact-subject-of-another-report
>>
>> If you want to undo deduplication, reply with:
>> #syz undup

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