> On Jan 6, 2023, at 12:19 PM, Hou Tao <houtao1@xxxxxxxxxx> wrote:
>
> Hi,
>
> On 1/6/2023 10:13 AM, Xu Kuohai wrote:
>> On 1/5/2023 7:27 PM, tong@xxxxxxxxxxxxx wrote:
>>> From: Tonghao Zhang <tong@xxxxxxxxxxxxx>
>>>
>>> The lock may be taken in both NMI and non-NMI contexts.
>>> There is a lockdep warning (inconsistent lock state), if
>>> enable lockdep. For performance, this patch doesn't use trylock,
>>> and disable lockdep temporarily.
>>>
>>> [ 82.474075] ================================
>>> [ 82.474076] WARNING: inconsistent lock state
>>> [ 82.474090] 6.1.0+ #48 Tainted: G E
>>> [ 82.474093] --------------------------------
>>> [ 82.474100] inconsistent {INITIAL USE} -> {IN-NMI} usage.
>>> [ 82.474101] kprobe-load/1740 [HC1[1]:SC0[0]:HE0:SE1] takes:
>>> [ 82.474105] ffff88860a5cf7b0 (&htab->lockdep_key){....}-{2:2}, at:
>>> htab_lock_bucket+0x61/0x6c
>>> [ 82.474120] {INITIAL USE} state was registered at:
>>> [ 82.474122] mark_usage+0x1d/0x11d
>>> [ 82.474130] __lock_acquire+0x3c9/0x6ed
>>> [ 82.474131] lock_acquire+0x23d/0x29a
>>> [ 82.474135] _raw_spin_lock_irqsave+0x43/0x7f
>>> [ 82.474148] htab_lock_bucket+0x61/0x6c
>>> [ 82.474151] htab_map_update_elem+0x11e/0x220
>>> [ 82.474155] bpf_map_update_value+0x267/0x28e
>>> [ 82.474160] map_update_elem+0x13e/0x17d
>>> [ 82.474164] __sys_bpf+0x2ae/0xb2e
>>> [ 82.474167] __do_sys_bpf+0xd/0x15
>>> [ 82.474171] do_syscall_64+0x6d/0x84
>>> [ 82.474174] entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>> [ 82.474178] irq event stamp: 1496498
>>> [ 82.474180] hardirqs last enabled at (1496497): [<ffffffff817eb9d9>]
>>> syscall_enter_from_user_mode+0x63/0x8d
>>> [ 82.474184] hardirqs last disabled at (1496498): [<ffffffff817ea6b6>]
>>> exc_nmi+0x87/0x109
>>> [ 82.474187] softirqs last enabled at (1446698): [<ffffffff81a00347>]
>>> __do_softirq+0x347/0x387
>>> [ 82.474191] softirqs last disabled at (1446693): [<ffffffff810b9b06>]
>>> __irq_exit_rcu+0x67/0xc6
>>> [ 82.474195]
>>> [ 82.474195] other info that might help us debug this:
>>> [ 82.474196] Possible unsafe locking scenario:
>>> [ 82.474196]
>>> [ 82.474197] CPU0
>>> [ 82.474198] ----
>>> [ 82.474198] lock(&htab->lockdep_key);
>>> [ 82.474200] <Interrupt>
>>> [ 82.474200] lock(&htab->lockdep_key);
>>> [ 82.474201]
>>> [ 82.474201] *** DEADLOCK ***
>>> [ 82.474201]
>>> [ 82.474202] no locks held by kprobe-load/1740.
>>> [ 82.474203]
>>> [ 82.474203] stack backtrace:
>>> [ 82.474205] CPU: 14 PID: 1740 Comm: kprobe-load Tainted: G
>>> E 6.1.0+ #48
>>> [ 82.474208] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
>>> rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
>>> [ 82.474213] Call Trace:
>>> [ 82.474218] <NMI>
>>> [ 82.474224] dump_stack_lvl+0x57/0x81
>>> [ 82.474228] lock_acquire+0x1f4/0x29a
>>> [ 82.474233] ? htab_lock_bucket+0x61/0x6c
>>> [ 82.474237] ? rcu_read_lock_held_common+0xe/0x38
>>> [ 82.474245] _raw_spin_lock_irqsave+0x43/0x7f
>>> [ 82.474249] ? htab_lock_bucket+0x61/0x6c
>>> [ 82.474253] htab_lock_bucket+0x61/0x6c
>>> [ 82.474257] htab_map_update_elem+0x11e/0x220
>>> [ 82.474264] bpf_prog_df326439468c24a9_bpf_prog1+0x41/0x45
>>> [ 82.474276] bpf_trampoline_6442457183_0+0x43/0x1000
>>> [ 82.474283] nmi_handle+0x5/0x254
>>> [ 82.474289] default_do_nmi+0x3d/0xf6
>>> [ 82.474293] exc_nmi+0xa1/0x109
>>> [ 82.474297] end_repeat_nmi+0x16/0x67
>>> [ 82.474300] RIP: 0010:cpu_online+0xa/0x12
>>> [ 82.474308] Code: 08 00 00 00 39 c6 0f 43 c6 83 c0 07 83 e0 f8 c3 cc cc cc
>>> cc 0f 1f 44 00 00 31 c0 c3 cc cc cc cc 89 ff 48 0f a3 3d 5f 52 75 01 <0f> 92
>>> c0 c3 cc cc cc cc 55 48 89 e5 41 57 49 89 f7 41 56 49 896
>>> [ 82.474310] RSP: 0018:ffffc9000131bd38 EFLAGS: 00000283
>>> [ 82.474313] RAX: ffff88860b85fe78 RBX: 0000000000102cc0 RCX: 0000000000000008
>>> [ 82.474315] RDX: 0000000000000004 RSI: ffff88860b85fe78 RDI: 000000000000000e
>>> [ 82.474316] RBP: 00000000ffffffff R08: 0000000000102cc0 R09: 00000000ffffffff
>>> [ 82.474318] R10: 0000000000000001 R11: 0000000000000000 R12: ffff888100042200
>>> [ 82.474320] R13: 0000000000000004 R14: ffffffff81271dc2 R15: ffff88860b85fe78
>>> [ 82.474322] ? kvmalloc_node+0x44/0xd2
>>> [ 82.474333] ? cpu_online+0xa/0x12
>>> [ 82.474338] ? cpu_online+0xa/0x12
>>> [ 82.474342] </NMI>
>>> [ 82.474343] <TASK>
>>> [ 82.474343] trace_kmalloc+0x7c/0xe6
>>> [ 82.474347] ? kvmalloc_node+0x44/0xd2
>>> [ 82.474350] __kmalloc_node+0x9a/0xaf
>>> [ 82.474354] kvmalloc_node+0x44/0xd2
>>> [ 82.474359] kvmemdup_bpfptr+0x29/0x66
>>> [ 82.474363] map_update_elem+0x119/0x17d
>>> [ 82.474370] __sys_bpf+0x2ae/0xb2e
>>> [ 82.474380] __do_sys_bpf+0xd/0x15
>>> [ 82.474384] do_syscall_64+0x6d/0x84
>>> [ 82.474387] entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>> [ 82.474391] RIP: 0033:0x7fe75d4f752d
>>> [ 82.474394] Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 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 8b 0d 2b 79 2c 00 f7 d8 64 89 018
>>> [ 82.474396] RSP: 002b:00007ffe95d1cd78 EFLAGS: 00000246 ORIG_RAX:
>>> 0000000000000141
>>> [ 82.474398] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fe75d4f752d
>>> [ 82.474400] RDX: 0000000000000078 RSI: 00007ffe95d1cd80 RDI: 0000000000000002
>>> [ 82.474401] RBP: 00007ffe95d1ce30 R08: 0000000000000000 R09: 0000000000000004
>>> [ 82.474403] R10: 00007ffe95d1cd80 R11: 0000000000000246 R12: 00000000004007f0
>>> [ 82.474405] R13: 00007ffe95d1cf10 R14: 0000000000000000 R15: 0000000000000000
>>> [ 82.474412] </TASK>
>>>
>>> Signed-off-by: Tonghao Zhang <tong@xxxxxxxxxxxxx>
>>> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
>>> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
>>> Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
>>> Cc: Martin KaFai Lau <martin.lau@xxxxxxxxx>
>>> Cc: Song Liu <song@xxxxxxxxxx>
>>> Cc: Yonghong Song <yhs@xxxxxx>
>>> Cc: John Fastabend <john.fastabend@xxxxxxxxx>
>>> Cc: KP Singh <kpsingh@xxxxxxxxxx>
>>> Cc: Stanislav Fomichev <sdf@xxxxxxxxxx>
>>> Cc: Hao Luo <haoluo@xxxxxxxxxx>
>>> Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
>>> Cc: Hou Tao <houtao1@xxxxxxxxxx>
>>> ---
>>> previous discussion:
>>> https://lore.kernel.org/all/20221121100521.56601-2-xiangxia.m.yue@xxxxxxxxx/
>>> ---
>>> kernel/bpf/hashtab.c | 16 ++++++++++++++++
>>> 1 file changed, 16 insertions(+)
>>>
>>> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
>>> index 974f104f47a0..146433c9bd1a 100644
>>> --- a/kernel/bpf/hashtab.c
>>> +++ b/kernel/bpf/hashtab.c
>>> @@ -161,6 +161,19 @@ static inline int htab_lock_bucket(const struct bpf_htab
>>> *htab,
>>> return -EBUSY;
>>> }
>>> + /*
>>> + * The lock may be taken in both NMI and non-NMI contexts.
>>> + * There is a lockdep warning (inconsistent lock state), if
>>> + * enable lockdep. The potential deadlock happens when the
>>> + * lock is contended from the same cpu. map_locked rejects
>>> + * concurrent access to the same bucket from the same CPU.
>>> + * When the lock is contended from a remote cpu, we would
>>> + * like the remote cpu to spin and wait, instead of giving
>>> + * up immediately. As this gives better throughput. So replacing
>>> + * the current raw_spin_lock_irqsave() with trylock sacrifices
>>> + * this performance gain. lockdep_off temporarily.
>>> + */
>>> + lockdep_off();
>>
>> seems it's better to define map_locked as a raw spin lock and use
>> trylock(map_locked[hash])
>> to check if this cpu has locked the bucket.
> Redefining map_locked as per-cpu raw spinlock array seems a good idea, so we
Yes, one question, do this drop performance compared with atomic.
> don't need to call lock_acquire() and lock_release() manually. But lockdep_off()
> is still needed here, else there will always be lockdep warning.
>>
>>> raw_spin_lock_irqsave(&b->raw_lock, flags);
>>> *pflags = flags;
>>> @@ -172,7 +185,10 @@ static inline void htab_unlock_bucket(const struct
>>> bpf_htab *htab,
>>> unsigned long flags)
>>> {
>>> hash = hash & min_t(u32, HASHTAB_MAP_LOCK_MASK, htab->n_buckets -1);
>>> +
>>> raw_spin_unlock_irqrestore(&b->raw_lock, flags);
>>> + lockdep_on();
>>> +
>>> __this_cpu_dec(*(htab->map_locked[hash]));
>>> preempt_enable();
>>> }
>>
>> .
