[syzbot] [net?] INFO: rcu detected stall in ip_list_rcv (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 753c8608f3e5 Merge tag 'for-netdev' of https://git.kernel...
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1381f352e80000
kernel config: https://syzkaller.appspot.com/x/.config?x=f8715b6ede5c4b90
dashboard link: https://syzkaller.appspot.com/bug?extid=45b67ef6e09a39a2cbcd
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=15abc0e2e80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10b0c7c2e80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/17dd61ceadb9/disk-753c8608.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/fed6ba43d9bd/vmlinux-753c8608.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3e68e49966d3/bzImage-753c8608.xz

The issue was bisected to:

commit b5b73b26b3ca34574124ed7ae9c5ba8391a7f176
Author: Vinicius Costa Gomes <viniciu...@intel.com>
Date: Thu Sep 10 00:03:11 2020 +0000

taprio: Fix allowing too small intervals

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=13b90672e80000
final oops: https://syzkaller.appspot.com/x/report.txt?x=10790672e80000
console output: https://syzkaller.appspot.com/x/log.txt?x=17b90672e80000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+45b67e...@syzkaller.appspotmail.com
Fixes: b5b73b26b3ca ("taprio: Fix allowing too small intervals")

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 0-...!: (2 GPs behind) idle=9444/0/0x3 softirq=6168/6168 fqs=0
rcu: (detected by 1, t=10504 jiffies, g=7341, q=186 ncpus=2)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.7.0-rc3-syzkaller-00666-g753c8608f3e5 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
RIP: 0010:rcu_is_watching+0x7c/0xb0 kernel/rcu/tree.c:701
Code: 89 da 48 c1 ea 03 0f b6 14 02 48 89 d8 83 e0 07 83 c0 03 38 d0 7c 04 84 d2 75 1c 8b 03 c1 e8 02 83 e0 01 65 ff 0d fc d9 93 7e <74> 03 5b 5d c3 e8 fa 9d 90 ff 5b 5d c3 48 89 df e8 bf 90 6e 00 eb
RSP: 0000:ffffc90000006b90 EFLAGS: 00000006
RAX: 0000000000000001 RBX: ffff8880b9836de8 RCX: ffffffff81680cf5
RDX: 0000000000000000 RSI: ffffffff8b2f1340 RDI: ffffffff8ca6ea60
RBP: 0000000000000000 R08: 0000000000000000 R09: fffffbfff1e31dea
R10: ffffffff8f18ef57 R11: 0000000000000004 R12: ffff8880b982b958
R13: 179cc057f149e962 R14: ffff88807627b340 R15: ffffffff88a26e60
FS: 0000000000000000(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f3bc135f410 CR3: 000000001ab22000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<NMI>
</NMI>
<IRQ>
trace_lock_release include/trace/events/lock.h:69 [inline]
lock_release+0x4bf/0x690 kernel/locking/lockdep.c:5765
__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:149 [inline]
_raw_spin_unlock_irqrestore+0x1a/0x70 kernel/locking/spinlock.c:194
__run_hrtimer kernel/time/hrtimer.c:1684 [inline]
__hrtimer_run_queues+0x58b/0xc20 kernel/time/hrtimer.c:1752
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+0x43/0xb0 arch/x86/kernel/apic/apic.c:1076
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:645
RIP: 0010:unwind_get_return_address+0xa1/0xe0 arch/x86/kernel/unwind_orc.c:369
Code: 00 31 ff 89 c5 89 c6 e8 8d 9d 4d 00 85 ed 74 b9 e8 14 a2 4d 00 4c 89 e2 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 80 3c 02 00 <75> 28 48 8b 5b 48 e8 f4 a1 4d 00 48 89 d8 5b 5d 41 5c c3 48 89 df
RSP: 0000:ffffc90000006f08 EFLAGS: 00000246
RAX: dffffc0000000000 RBX: ffffc90000006f30 RCX: ffffffff8139f033
RDX: 1ffff92000000def RSI: ffffffff8139f03c RDI: 0000000000000005
RBP: 0000000000000001 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000003 R12: ffffc90000006f78
R13: ffffffff8174f4a0 R14: ffffc90000006ff0 R15: ffffffff8cc95900
arch_stack_walk+0xbe/0x170 arch/x86/kernel/stacktrace.c:26
stack_trace_save+0x96/0xd0 kernel/stacktrace.c:122
kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
kasan_set_track+0x25/0x30 mm/kasan/common.c:52
kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:522
____kasan_slab_free mm/kasan/common.c:236 [inline]
____kasan_slab_free+0x15b/0x1b0 mm/kasan/common.c:200
kasan_slab_free include/linux/kasan.h:164 [inline]
slab_free_hook mm/slub.c:1800 [inline]
slab_free_freelist_hook+0x114/0x1e0 mm/slub.c:1826
slab_free mm/slub.c:3809 [inline]
kmem_cache_free+0xf8/0x350 mm/slub.c:3831
kfree_skbmem+0xef/0x1b0 net/core/skbuff.c:1015
tcp_rcv_established+0xd5f/0x20e0 net/ipv4/tcp_input.c:6065
tcp_v4_do_rcv+0x68c/0xa10 net/ipv4/tcp_ipv4.c:1912
tcp_v4_rcv+0x3892/0x3b40 net/ipv4/tcp_ipv4.c:2335
ip_protocol_deliver_rcu+0x9f/0x480 net/ipv4/ip_input.c:205
ip_local_deliver_finish+0x2e4/0x510 net/ipv4/ip_input.c:233
NF_HOOK include/linux/netfilter.h:314 [inline]
NF_HOOK include/linux/netfilter.h:308 [inline]
ip_local_deliver+0x18e/0x1f0 net/ipv4/ip_input.c:254
dst_input include/net/dst.h:461 [inline]
ip_sublist_rcv_finish+0x99/0x2e0 net/ipv4/ip_input.c:580
ip_list_rcv_finish.constprop.0+0x560/0x720 net/ipv4/ip_input.c:631
ip_sublist_rcv net/ipv4/ip_input.c:639 [inline]
ip_list_rcv+0x339/0x440 net/ipv4/ip_input.c:674
__netif_receive_skb_list_ptype net/core/dev.c:5572 [inline]
__netif_receive_skb_list_core+0x52c/0x8a0 net/core/dev.c:5620
__netif_receive_skb_list net/core/dev.c:5672 [inline]
netif_receive_skb_list_internal+0x769/0xe00 net/core/dev.c:5763
gro_normal_list include/net/gro.h:439 [inline]
gro_normal_list include/net/gro.h:435 [inline]
napi_complete_done+0x23f/0x990 net/core/dev.c:6103
virtqueue_napi_complete drivers/net/virtio_net.c:440 [inline]
virtnet_poll+0xf4a/0x15d0 drivers/net/virtio_net.c:2158
__napi_poll.constprop.0+0xb4/0x540 net/core/dev.c:6533
napi_poll net/core/dev.c:6602 [inline]
net_rx_action+0x956/0xe90 net/core/dev.c:6735
__do_softirq+0x21a/0x8de 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
common_interrupt+0xb0/0xd0 arch/x86/kernel/irq.c:247
</IRQ>
<TASK>
asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:636
RIP: 0010:native_irq_disable arch/x86/include/asm/irqflags.h:37 [inline]
RIP: 0010:arch_local_irq_disable arch/x86/include/asm/irqflags.h:72 [inline]
RIP: 0010:acpi_safe_halt+0x1b/0x20 drivers/acpi/processor_idle.c:113
Code: ed c3 66 66 2e 0f 1f 84 00 00 00 00 00 66 90 65 48 8b 04 25 c0 bc 03 00 48 8b 00 a8 08 75 0c 66 90 0f 00 2d b7 7b ba 00 fb f4 <fa> c3 0f 1f 00 0f b6 47 08 3c 01 74 0b 3c 02 74 05 8b 7f 04 eb 9f
RSP: 0000:ffffffff8cc07d68 EFLAGS: 00000246
RAX: 0000000000004000 RBX: 0000000000000001 RCX: ffffffff8a7fa837
RDX: 0000000000000001 RSI: ffff888014ebd800 RDI: ffff888014ebd864
RBP: ffff888014ebd864 R08: 0000000000000001 R09: ffffed1017306dbd
R10: ffff8880b9836deb R11: 0000000000000000 R12: ffff8881412c4000
R13: ffffffff8db1cf20 R14: 0000000000000000 R15: 0000000000000000
acpi_idle_enter+0xc5/0x160 drivers/acpi/processor_idle.c:707
cpuidle_enter_state+0x83/0x500 drivers/cpuidle/cpuidle.c:267
cpuidle_enter+0x4e/0xa0 drivers/cpuidle/cpuidle.c:388
cpuidle_idle_call kernel/sched/idle.c:215 [inline]
do_idle+0x319/0x400 kernel/sched/idle.c:282
cpu_startup_entry+0x50/0x60 kernel/sched/idle.c:380
rest_init+0x16f/0x2b0 init/main.c:730
arch_call_rest_init+0x13/0x30 init/main.c:827
start_kernel+0x39f/0x480 init/main.c:1072
x86_64_start_reservations+0x18/0x30 arch/x86/kernel/head64.c:555
x86_64_start_kernel+0xb2/0xc0 arch/x86/kernel/head64.c:536
secondary_startup_64_no_verify+0x166/0x16b
</TASK>
INFO: NMI handler (nmi_cpu_backtrace_handler) took too long to run: 5.004 msecs
rcu: rcu_preempt kthread starved for 10504 jiffies! g7341 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
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:R running task stack:28752 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>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 1 PID: 5093 Comm: syz-executor163 Not tainted 6.7.0-rc3-syzkaller-00666-g753c8608f3e5 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
RIP: 0010:kvm_wait+0x146/0x180 arch/x86/kernel/kvm.c:1062
Code: 5b 5d 41 5c 41 5d e9 c9 34 4e 00 e8 c4 34 4e 00 e8 8f ed 54 00 66 90 e8 b8 34 4e 00 0f 00 2d 41 5a 90 09 e8 ac 34 4e 00 fb f4 <5b> 5d 41 5c 41 5d e9 9f 34 4e 00 e8 9a 34 4e 00 e8 d5 ed 54 00 e9
RSP: 0018:ffffc900001f0ae0 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 0000000000000003 RCX: 1ffffffff23ec48c
RDX: ffff888076299dc0 RSI: ffffffff81395da4 RDI: ffffffff8b2f13c0
RBP: ffff88807e768098 R08: 0000000000000001 R09: fffffbfff23e29e7
R10: ffffffff91f14f3f R11: 0000000000000002 R12: 0000000000000003
R13: 0000000000000003 R14: 0000000000000000 R15: ffffed100fced013
FS: 0000000000000000(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f3bc14032d0 CR3: 000000007af32000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
pv_wait arch/x86/include/asm/paravirt.h:598 [inline]
pv_wait_head_or_lock kernel/locking/qspinlock_paravirt.h:470 [inline]
__pv_queued_spin_lock_slowpath+0x959/0xc70 kernel/locking/qspinlock.c:511
pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:586 [inline]
queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:51 [inline]
queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
do_raw_spin_lock+0x20e/0x2b0 kernel/locking/spinlock_debug.c:115
spin_lock include/linux/spinlock.h:351 [inline]
tcp_write_timer+0x2a/0x2b0 net/ipv4/tcp_timer.c:708
call_timer_fn+0x193/0x590 kernel/time/timer.c:1700
expire_timers kernel/time/timer.c:1751 [inline]
__run_timers+0x764/0xb20 kernel/time/timer.c:2022
run_timer_softirq+0x58/0xd0 kernel/time/timer.c:2035
__do_softirq+0x21a/0x8de 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+0x95/0xb0 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:csd_lock_wait kernel/smp.c:311 [inline]
RIP: 0010:smp_call_function_many_cond+0x4e4/0x1550 kernel/smp.c:855
Code: 0b 00 85 ed 74 4d 48 b8 00 00 00 00 00 fc ff df 4d 89 f4 4c 89 f5 49 c1 ec 03 83 e5 07 49 01 c4 83 c5 03 e8 8e c0 0b 00 f3 90 <41> 0f b6 04 24 40 38 c5 7c 08 84 c0 0f 85 24 0e 00 00 8b 43 08 31
RSP: 0018:ffffc90003bffa48 EFLAGS: 00000293
RAX: 0000000000000000 RBX: ffff8880b98441a0 RCX: ffffffff817bd1e8
RDX: ffff888076299dc0 RSI: ffffffff817bd1c2 RDI: 0000000000000005
RBP: 0000000000000003 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: ffffed1017308835
R13: 0000000000000001 R14: ffff8880b98441a8 R15: ffff8880b993d8c0
on_each_cpu_cond_mask+0x40/0x90 kernel/smp.c:1023
__flush_tlb_multi arch/x86/include/asm/paravirt.h:87 [inline]
flush_tlb_multi arch/x86/mm/tlb.c:944 [inline]
flush_tlb_mm_range+0x28f/0x320 arch/x86/mm/tlb.c:1030
tlb_flush arch/x86/include/asm/tlb.h:20 [inline]
tlb_flush_mmu_tlbonly include/asm-generic/tlb.h:458 [inline]
tlb_flush_mmu_tlbonly include/asm-generic/tlb.h:448 [inline]
tlb_flush_mmu mm/mmu_gather.c:299 [inline]
tlb_finish_mmu+0x335/0x6f0 mm/mmu_gather.c:392
exit_mmap+0x38b/0xa70 mm/mmap.c:3321
__mmput+0x12a/0x4d0 kernel/fork.c:1349
mmput+0x62/0x70 kernel/fork.c:1371
exit_mm kernel/exit.c:567 [inline]
do_exit+0x9ad/0x2ae0 kernel/exit.c:858
do_group_exit+0xd4/0x2a0 kernel/exit.c:1021
__do_sys_exit_group kernel/exit.c:1032 [inline]
__se_sys_exit_group kernel/exit.c:1030 [inline]
__x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1030
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: 0033:0x7f3bc13802e9
Code: Unable to access opcode bytes at 0x7f3bc13802bf.
RSP: 002b:00007ffde3662848 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f3bc13802e9
RDX: 000000000000003c RSI: 00000000000000e7 RDI: 0000000000000000
RBP: 00007f3bc1400390 R08: ffffffffffffffb8 R09: 0000000100000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f3bc1400390
R13: 0000000000000000 R14: 00007f3bc1402ec0 R15: 00007f3bc13507c0
</TASK>


---
This report is generated by a bot. It may contain errors.
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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:
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#syz undup

[Eric Dumazet]

FYI : Many other syzbot reports are pointing to taprio these days.

In a3d43c0d56f1b94e74963a2fbadfb70126d92213 ("taprio: Add support
adding an admin schedule"),
advance_sched() was changed to call switch_schedules(q, &admin, &oper);

This is done while qdisc spinlock is not held, I fail to see how this
can work safely ?

Which lock is supposed to protect q->oper_sched and q->admin_sched ?

This can not be q->current_entry_lock in some cases, and qdisc lock in others.

[Jamal Hadi Salim]

Vinicius,
This one has a reproducer. Can you please take a look - and note what
Eric is saying here.
In some cases for example the code is invoking from the timer while
not holding the qdisc spinlock.

cheers,
jamal

[Eric Dumazet]

On Fri, Dec 15, 2023 at 10:37 PM Vinicius Costa Gomes
<viniciu...@intel.com> wrote:

> I know, it's bothering me a lot, really.
>
> I'll investigate this one a bit better, and see if I can come up with
> a fix for the short term.
>
> For the long term, I am thinking that the solution is to re-write the
> taprio software mode "engine" to not be 'hrtimer' dependent. And it will
> have the advantage that I would be able to unify some of the code for
> "txtime-assisted mode" and software mode, i.e. the "get the schedule
> entry for a particular time" function will be the used for both.

>
> > In a3d43c0d56f1b94e74963a2fbadfb70126d92213 ("taprio: Add support
> > adding an admin schedule"),
> > advance_sched() was changed to call switch_schedules(q, &admin, &oper);
> >
> > This is done while qdisc spinlock is not held, I fail to see how this
> > can work safely ?
> >
>

> I took a look at the code at a3d43c0d56f1b94e74963a2fbadfb70126d92213
> point, there are two calls to switch_schedules() and both calls to
> switch_schedules() (both in advance_sched()) are done with the lock held
> (q->current_entry_lock). Am I missing anything?
>
> But the situation in the current code is definitely worse, I admit,
> there are two additional calls to switch_schedules(), one in
> get_packet_txtime() and one in taprio_offload_config_changed(), these
> are done without the lock, but in these modes the hrtimer isn't running.
>
> I will send a patch fixing this, adding locking for those two extra
> cases as well.

>
> > Which lock is supposed to protect q->oper_sched and q->admin_sched ?
> >
> > This can not be q->current_entry_lock in some cases, and qdisc lock in others.
> >
>

> It should have been q->current_entry_lock.
>

If this helps, here is one trace that led to my questions:

BUG: KASAN: slab-use-after-free in advance_sched+0xc03/0xc60
net/sched/sch_taprio.c:953
Read of size 8 at addr ffff888027fbc910 by task kworker/u4:6/6820

CPU: 0 PID: 6820 Comm: kworker/u4:6 Not tainted
6.7.0-rc4-syzkaller-00954-g1b666016d0ad #0

Hardware name: Google Google Compute Engine/Google Compute Engine,

BIOS Google 11/17/2023
Workqueue: bat_events batadv_purge_orig
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:364 [inline]
print_report+0xc4/0x620 mm/kasan/report.c:475
kasan_report+0xda/0x110 mm/kasan/report.c:588
advance_sched+0xc03/0xc60 net/sched/sch_taprio.c:953
__run_hrtimer kernel/time/hrtimer.c:1688 [inline]
__hrtimer_run_queues+0x203/0xc20 kernel/time/hrtimer.c:1752

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:649
RIP: 0010:lock_acquire+0x1ef/0x520 kernel/locking/lockdep.c:5722
Code: c1 05 6d 69 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:ffffc900042afa88 EFLAGS: 00000206
RAX: dffffc0000000000 RBX: 1ffff92000855f53 RCX: ffffffff81672f5e
RDX: 0000000000000001 RSI: ffffffff8accbc20 RDI: ffffffff8b2f13e0
RBP: 0000000000000200 R08: 0000000000000000 R09: fffffbfff23e2deb
R10: ffffffff91f16f5f R11: 0000000000000002 R12: 0000000000000001
R13: 0000000000000000 R14: ffff88803c2bda18 R15: 0000000000000000
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
_raw_spin_lock_bh+0x33/0x40 kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:356 [inline]
batadv_purge_orig_ref+0x16d/0x1520 net/batman-adv/originator.c:1271
batadv_purge_orig+0x19/0x60 net/batman-adv/originator.c:1300
process_one_work+0x886/0x15d0 kernel/workqueue.c:2627
process_scheduled_works kernel/workqueue.c:2700 [inline]
worker_thread+0x8b9/0x1290 kernel/workqueue.c:2781

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>

Allocated by task 13485:

kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
kasan_set_track+0x25/0x30 mm/kasan/common.c:52

____kasan_kmalloc mm/kasan/common.c:374 [inline]
__kasan_kmalloc+0xa2/0xb0 mm/kasan/common.c:383
kmalloc include/linux/slab.h:600 [inline]
kzalloc include/linux/slab.h:721 [inline]
taprio_change+0x55a/0x38d0 net/sched/sch_taprio.c:1881
qdisc_change net/sched/sch_api.c:1387 [inline]
tc_modify_qdisc+0x7d5/0x1c30 net/sched/sch_api.c:1717
rtnetlink_rcv_msg+0x3c7/0xe00 net/core/rtnetlink.c:6566
netlink_rcv_skb+0x16b/0x440 net/netlink/af_netlink.c:2544
netlink_unicast_kernel net/netlink/af_netlink.c:1341 [inline]
netlink_unicast+0x53b/0x810 net/netlink/af_netlink.c:1367
netlink_sendmsg+0x8b7/0xd70 net/netlink/af_netlink.c:1909
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg+0xd5/0x180 net/socket.c:745
____sys_sendmsg+0x6ac/0x940 net/socket.c:2584
___sys_sendmsg+0x135/0x1d0 net/socket.c:2638
__sys_sendmsg+0x117/0x1e0 net/socket.c:2667
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x40/0x110 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

Freed by task 13492:

kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
kasan_set_track+0x25/0x30 mm/kasan/common.c:52
kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:522
____kasan_slab_free mm/kasan/common.c:236 [inline]
____kasan_slab_free+0x15b/0x1b0 mm/kasan/common.c:200
kasan_slab_free include/linux/kasan.h:164 [inline]
slab_free_hook mm/slub.c:1800 [inline]
slab_free_freelist_hook+0x114/0x1e0 mm/slub.c:1826
slab_free mm/slub.c:3809 [inline]

__kmem_cache_free+0xc0/0x180 mm/slub.c:3822
rcu_do_batch kernel/rcu/tree.c:2158 [inline]
rcu_core+0x819/0x1680 kernel/rcu/tree.c:2431
__do_softirq+0x21a/0x8de kernel/softirq.c:553

Last potentially related work creation:
kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
__kasan_record_aux_stack+0xbc/0xd0 mm/kasan/generic.c:492
__call_rcu_common.constprop.0+0x9a/0x7a0 kernel/rcu/tree.c:2681
taprio_change+0x28f8/0x38d0 net/sched/sch_taprio.c:1991
qdisc_change net/sched/sch_api.c:1387 [inline]
tc_modify_qdisc+0x7d5/0x1c30 net/sched/sch_api.c:1717
rtnetlink_rcv_msg+0x3c7/0xe00 net/core/rtnetlink.c:6566
netlink_rcv_skb+0x16b/0x440 net/netlink/af_netlink.c:2544
netlink_unicast_kernel net/netlink/af_netlink.c:1341 [inline]
netlink_unicast+0x53b/0x810 net/netlink/af_netlink.c:1367
netlink_sendmsg+0x8b7/0xd70 net/netlink/af_netlink.c:1909
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg+0xd5/0x180 net/socket.c:745
____sys_sendmsg+0x6ac/0x940 net/socket.c:2584
___sys_sendmsg+0x135/0x1d0 net/socket.c:2638
__sys_sendmsg+0x117/0x1e0 net/socket.c:2667
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x40/0x110 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

Second to last potentially related work creation:
kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
__kasan_record_aux_stack+0xbc/0xd0 mm/kasan/generic.c:492
__call_rcu_common.constprop.0+0x9a/0x7a0 kernel/rcu/tree.c:2681
fib6_info_release include/net/ip6_fib.h:333 [inline]
nsim_rt6_release drivers/net/netdevsim/fib.c:515 [inline]
nsim_fib6_event_fini+0x1b1/0x280 drivers/net/netdevsim/fib.c:841
nsim_fib_event drivers/net/netdevsim/fib.c:891 [inline]
nsim_fib_event_work+0x2fe/0x26e0 drivers/net/netdevsim/fib.c:1492
process_one_work+0x886/0x15d0 kernel/workqueue.c:2627
process_scheduled_works kernel/workqueue.c:2700 [inline]
worker_thread+0x8b9/0x1290 kernel/workqueue.c:2781

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

The buggy address belongs to the object at ffff888027fbc800
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 272 bytes inside of
freed 512-byte region [ffff888027fbc800, ffff888027fbca00)

The buggy address belongs to the physical page:
page:ffffea00009fef00 refcount:1 mapcount:0 mapping:0000000000000000
index:0x0 pfn:0x27fbc
head:ffffea00009fef00 order:2 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000840 ffff888013041c80 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask
0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC),
pid 3285, tgid 3285 (kworker/u4:2), ts 18559127120, free_ts 0
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x2d0/0x350 mm/page_alloc.c:1544
prep_new_page mm/page_alloc.c:1551 [inline]
get_page_from_freelist+0xa28/0x3730 mm/page_alloc.c:3319
__alloc_pages+0x22e/0x2420 mm/page_alloc.c:4575
alloc_pages_mpol+0x258/0x5f0 mm/mempolicy.c:2133
alloc_slab_page mm/slub.c:1870 [inline]
allocate_slab mm/slub.c:2017 [inline]
new_slab+0x283/0x3c0 mm/slub.c:2070
___slab_alloc+0x979/0x1500 mm/slub.c:3223
__slab_alloc.constprop.0+0x56/0xa0 mm/slub.c:3322
__slab_alloc_node mm/slub.c:3375 [inline]
slab_alloc_node mm/slub.c:3468 [inline]
__kmem_cache_alloc_node+0x131/0x310 mm/slub.c:3517
kmalloc_trace+0x25/0x60 mm/slab_common.c:1098
kmalloc include/linux/slab.h:600 [inline]
kzalloc include/linux/slab.h:721 [inline]
alloc_bprm+0x51/0xb00 fs/exec.c:1512
kernel_execve+0xaf/0x4e0 fs/exec.c:1987
call_usermodehelper_exec_async+0x256/0x4c0 kernel/umh.c:110

ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

page_owner free stack trace missing

Memory state around the buggy address:
ffff888027fbc800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888027fbc880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888027fbc900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888027fbc980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888027fbca00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================
----------------
Code disassembly (best guess):
0: c1 05 6d 69 9a 7e 83 roll $0x83,0x7e9a696d(%rip) # 0x7e9a6974
7: f8 clc
8: 01 0f add %ecx,(%rdi)
a: 85 b4 02 00 00 9c 58 test %esi,0x589c0000(%rdx,%rax,1)
11: f6 c4 02 test $0x2,%ah
14: 0f 85 9f 02 00 00 jne 0x2b9
1a: 48 85 ed test %rbp,%rbp
1d: 74 01 je 0x20
1f: fb sti
20: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
27: fc ff df
* 2a: 48 01 c3 add %rax,%rbx <-- trapping instruction
2d: 48 c7 03 00 00 00 00 movq $0x0,(%rbx)
34: 48 c7 43 08 00 00 00 movq $0x0,0x8(%rbx)
3b: 00
3c: 48 rex.W
3d: 8b .byte 0x8b
3e: 84 .byte 0x84
3f: 24 .byte 0x24

[Vinicius Costa Gomes]

Sure, taking a look.

> In some cases for example the code is invoking from the timer while
> not holding the qdisc spinlock.
>
> cheers,
> jamal
>
>> FYI : Many other syzbot reports are pointing to taprio these days.
>>
>> In a3d43c0d56f1b94e74963a2fbadfb70126d92213 ("taprio: Add support
>> adding an admin schedule"),
>> advance_sched() was changed to call switch_schedules(q, &admin, &oper);
>>
>> This is done while qdisc spinlock is not held, I fail to see how this
>> can work safely ?
>>
>> Which lock is supposed to protect q->oper_sched and q->admin_sched ?
>>
>> This can not be q->current_entry_lock in some cases, and qdisc lock in others.
>

Cheers,
--
Vinicius

[Vinicius Costa Gomes]

I know, it's bothering me a lot, really.

I'll investigate this one a bit better, and see if I can come up with
a fix for the short term.

For the long term, I am thinking that the solution is to re-write the
taprio software mode "engine" to not be 'hrtimer' dependent. And it will
have the advantage that I would be able to unify some of the code for
"txtime-assisted mode" and software mode, i.e. the "get the schedule
entry for a particular time" function will be the used for both.

> In a3d43c0d56f1b94e74963a2fbadfb70126d92213 ("taprio: Add support
> adding an admin schedule"),
> advance_sched() was changed to call switch_schedules(q, &admin, &oper);
>
> This is done while qdisc spinlock is not held, I fail to see how this
> can work safely ?
>

I took a look at the code at a3d43c0d56f1b94e74963a2fbadfb70126d92213
point, there are two calls to switch_schedules() and both calls to
switch_schedules() (both in advance_sched()) are done with the lock held
(q->current_entry_lock). Am I missing anything?

But the situation in the current code is definitely worse, I admit,
there are two additional calls to switch_schedules(), one in
get_packet_txtime() and one in taprio_offload_config_changed(), these
are done without the lock, but in these modes the hrtimer isn't running.

I will send a patch fixing this, adding locking for those two extra
cases as well.

> Which lock is supposed to protect q->oper_sched and q->admin_sched ?
>
> This can not be q->current_entry_lock in some cases, and qdisc lock in others.
>

It should have been q->current_entry_lock.

Cheers,
--
Vinicius