[syzbot] INFO: rcu detected stall in prog_array_map_clear_deferred

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 7c832d2f9b95 Add linux-next specific files for 20211015
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13d749ccb00000
kernel config: https://syzkaller.appspot.com/x/.config?x=f6ac42766a768877
dashboard link: https://syzkaller.appspot.com/bug?extid=1e372cc42ba6b9d90a6b
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1702b644b00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16f91334b00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1e372c...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 1-...!: (1 GPs behind) idle=38d/1/0x4000000000000000 softirq=10159/10160 fqs=234
(t=10500 jiffies g=11181 q=11)
rcu: rcu_preempt kthread starved for 9849 jiffies! g11181 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->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:R running task stack:29304 pid: 14 ppid: 2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:4965 [inline]
__schedule+0xa9a/0x4940 kernel/sched/core.c:6246
schedule+0xd2/0x260 kernel/sched/core.c:6319
schedule_timeout+0x14a/0x2a0 kernel/time/timer.c:1881
rcu_gp_fqs_loop+0x186/0x810 kernel/rcu/tree.c:1966
rcu_gp_kthread+0x1de/0x320 kernel/rcu/tree.c:2139
kthread+0x405/0x4f0 kernel/kthread.c:327
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
</TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 2713 Comm: kworker/0:3 Not tainted 5.15.0-rc5-next-20211015-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events prog_array_map_clear_deferred
RIP: 0010:check_preemption_disabled+0x2/0x170 lib/smp_processor_id.c:13
Code: 1f 44 00 00 e8 6f 16 4e f8 65 48 8b 3c 25 40 70 02 00 e8 41 43 05 f8 eb 99 0f 1f 44 00 00 0f 0b e9 23 ff ff ff cc cc cc 41 56 <41> 55 49 89 f5 41 54 55 48 89 fd 53 0f 1f 44 00 00 65 44 8b 25 cd
RSP: 0018:ffffc9000b95fa68 EFLAGS: 00000046
RAX: 0000000000000002 RBX: c8757c4f6cfa24cc RCX: ffffc9000b95fac8
RDX: 1ffff110046b014b RSI: ffffffff89ac08c0 RDI: ffffffff8a046f60
RBP: 1ffff9200172bf51 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000002
R13: 0000000000000003 R14: ffff888023580a60 R15: ffff888023580000
FS: 0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005555567352c0 CR3: 000000000b88e000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
lockdep_recursion_finish kernel/locking/lockdep.c:438 [inline]
lock_release+0x3bb/0x720 kernel/locking/lockdep.c:5659
__mutex_unlock_slowpath+0x99/0x5e0 kernel/locking/mutex.c:892
fd_array_map_delete_elem+0x1b0/0x2e0 kernel/bpf/arraymap.c:824
bpf_fd_array_map_clear kernel/bpf/arraymap.c:871 [inline]
prog_array_map_clear_deferred+0x10b/0x1b0 kernel/bpf/arraymap.c:1050
process_one_work+0x9b2/0x1690 kernel/workqueue.c:2297
worker_thread+0x658/0x11f0 kernel/workqueue.c:2444
kthread+0x405/0x4f0 kernel/kthread.c:327
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
</TASK>
NMI backtrace for cpu 1
CPU: 1 PID: 23 Comm: kworker/1:1 Not tainted 5.15.0-rc5-next-20211015-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events prog_array_map_clear_deferred
Call Trace:
<IRQ>
__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:105
nmi_trigger_cpumask_backtrace+0x1ae/0x220 lib/nmi_backtrace.c:62
trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
rcu_dump_cpu_stacks+0x25e/0x3f0 kernel/rcu/tree_stall.h:343
print_cpu_stall kernel/rcu/tree_stall.h:604 [inline]
check_cpu_stall kernel/rcu/tree_stall.h:688 [inline]
rcu_pending kernel/rcu/tree.c:3889 [inline]
rcu_sched_clock_irq.cold+0x9d/0x746 kernel/rcu/tree.c:2608
update_process_times+0x16d/0x200 kernel/time/timer.c:1785
tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:226
tick_sched_timer+0x1b0/0x2d0 kernel/time/tick-sched.c:1428
__run_hrtimer kernel/time/hrtimer.c:1685 [inline]
__hrtimer_run_queues+0x1c0/0xe50 kernel/time/hrtimer.c:1749
hrtimer_interrupt+0x31c/0x790 kernel/time/hrtimer.c:1811
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1086 [inline]
__sysvec_apic_timer_interrupt+0x146/0x530 arch/x86/kernel/apic/apic.c:1103
sysvec_apic_timer_interrupt+0x8e/0xc0 arch/x86/kernel/apic/apic.c:1097
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:638
RIP: 0010:lock_is_held_type+0xff/0x140 kernel/locking/lockdep.c:5685
Code: 00 00 b8 ff ff ff ff 65 0f c1 05 0c 1a b5 76 83 f8 01 75 29 9c 58 f6 c4 02 75 3d 48 f7 04 24 00 02 00 00 74 01 fb 48 83 c4 08 <44> 89 e8 5b 5d 41 5c 41 5d 41 5e 41 5f c3 45 31 ed eb b9 0f 0b 48
RSP: 0018:ffffc90000ddfa30 EFLAGS: 00000296
RAX: 0000000000000046 RBX: 0000000000000003 RCX: 0000000000000001
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffffff8bb82de0 R08: 0000000000000000 R09: ffffffff8d8fd297
R10: fffffbfff1b1fa52 R11: 0000000000000000 R12: ffff8880157b0000
R13: 0000000000000000 R14: 00000000ffffffff R15: ffff8880157b0ab8
lock_is_held include/linux/lockdep.h:283 [inline]
rcu_read_lock_sched_held+0x3a/0x70 kernel/rcu/update.c:125
trace_lock_release include/trace/events/lock.h:58 [inline]
lock_release+0x522/0x720 kernel/locking/lockdep.c:5648
__mutex_unlock_slowpath+0x99/0x5e0 kernel/locking/mutex.c:892
fd_array_map_delete_elem+0x1b0/0x2e0 kernel/bpf/arraymap.c:824
bpf_fd_array_map_clear kernel/bpf/arraymap.c:871 [inline]
prog_array_map_clear_deferred+0x10b/0x1b0 kernel/bpf/arraymap.c:1050
process_one_work+0x9b2/0x1690 kernel/workqueue.c:2297
worker_thread+0x658/0x11f0 kernel/workqueue.c:2444
kthread+0x405/0x4f0 kernel/kthread.c:327
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
</TASK>
----------------
Code disassembly (best guess), 1 bytes skipped:
0: 44 00 00 add %r8b,(%rax)
3: e8 6f 16 4e f8 callq 0xf84e1677
8: 65 48 8b 3c 25 40 70 mov %gs:0x27040,%rdi
f: 02 00
11: e8 41 43 05 f8 callq 0xf8054357
16: eb 99 jmp 0xffffffb1
18: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
1d: 0f 0b ud2
1f: e9 23 ff ff ff jmpq 0xffffff47
24: cc int3
25: cc int3
26: cc int3
27: 41 56 push %r14
* 29: 41 55 push %r13 <-- trapping instruction
2b: 49 89 f5 mov %rsi,%r13
2e: 41 54 push %r12
30: 55 push %rbp
31: 48 89 fd mov %rdi,%rbp
34: 53 push %rbx
35: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
3a: 65 gs
3b: 44 rex.R
3c: 8b .byte 0x8b
3d: 25 .byte 0x25
3e: cd .byte 0xcd


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[Eric Dumazet]

Repro allocates quite a big array.

bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_PROG_ARRAY, key_size=4, value_size=4, max_entries=268435458, map_flags=0, inner_map_fd=-1, map_name="", map_ifindex=0, btf_fd=-1, btf_key_type_id=0, btf_value_type_id=0, btf_vmlinux_value_type_id=0}, 64)

An ad-hoc cond_resched() would avoid this splat.

[Hillf Danton]

Even with rcu_preempt in place?

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.