From: Tonghao Zhang <tong@xxxxxxxxxxxxx>
There is a false lockdep warning (inconsistent lock state), if
enable lockdep. This is not a real deadlock issue. When the lock
is taken in non-NMI contexts, and then in NMI, there is a
warning as show below. For performance, this patch doesn't use
trylock, and disable lockdep only 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 | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 66bded144377..bff5118c6e7b 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -161,9 +161,24 @@ 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 false lockdep warning (inconsistent lock state),
+ * if lockdep enabled. 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. atomic map_locked is necessary.
+ * lockdep_off is invoked temporarily to fix the false warning.
+ */
+ lockdep_off();
raw_spin_lock_irqsave(&b->raw_lock, flags);
- *pflags = flags;
+ lockdep_on();
+ *pflags = flags;
return 0;
}
@@ -172,7 +187,11 @@ 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);
+
+ lockdep_off();
raw_spin_unlock_irqrestore(&b->raw_lock, flags);
+ lockdep_on();
+
__this_cpu_dec(*(htab->map_locked[hash]));
preempt_enable();
}
--
2.27.0
