最近又遇到一次hung,dmesg中堆栈如下:

[176223.913270] ------------[ cut here ]------------
[176223.913280] WARNING: CPU: PID: at net/sched/sch_generic.c: dev_watchdog+0x248/0x260-----注意cpu号是10
[176223.913282] NETDEV WATCHDOG: eth4 (ixgbe): transmit queue timed out----------------warn的内容
[176223.913283] Modules linked in: witdriver(OE) mysendmsg(OE) fuse tipc(OE) ossmod(OE) iptable_filter mptctl mptbase bonding dm_mirror dm_region_hash dm_log dm_mod iTCO_wdt iTCO_vendor_support skx_edac edac_core intel_powerclamp coretemp intel_rapl iosf_mbi kvm_intel kvm irqbypass crc32_pclmul ghash_clmulni_intel aesni_intel lrw gf128mul glue_helper ablk_helper cryptd pcspkr joydev ses enclosure sg mei_me mei shpchp lpc_ich i2c_i801 wmi ipmi_si ipmi_devintf ipmi_msghandler nfit libnvdimm acpi_power_meter acpi_cpufreq acpi_pad tcp_bbr sch_fq binfmt_misc ip_tables ext4 mbcache jbd2 raid1 sd_mod crc_t10dif crct10dif_generic ast i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm drm crct10dif_pclmul crct10dif_common crc32c_intel ahci libahci libata ixgbe(OE) i40e(OE) mpt3sas(OE)
[176223.913340] ptp raid_class pps_core scsi_transport_sas i2c_core dca [last unloaded: witdriver]
[176223.913347] CPU: PID: Comm: swapper/ Tainted: G OE ------------ 3.10.-693.21..el7.x86_64 #
[176223.913348] Hardware name: ZTE ZXCDN/SC621DI-16F, BIOS .0b //
[176223.913350] Call Trace:
[176223.913351] <IRQ> [<ffffffff816b2f9e>] dump_stack+0x19/0x1b
[176223.913361] [<ffffffff8108ae58>] __warn+0xd8/0x100----------------------warn了,内容见第二行
[176223.913364] [<ffffffff8108aedf>] warn_slowpath_fmt+0x5f/0x80
[176223.913369] [<ffffffff815bcc28>] dev_watchdog+0x248/0x260----------------在处理到dev_watchdog时候出现问题
[176223.913372] [<ffffffff815bc9e0>] ? dev_deactivate_queue.constprop.+0x60/0x60
[176223.913375] [<ffffffff8109a9c8>] call_timer_fn+0x38/0x110----------------处理回调
[176223.913378] [<ffffffff815bc9e0>] ? dev_deactivate_queue.constprop.+0x60/0x60
[176223.913382] [<ffffffff8109ceed>] run_timer_softirq+0x22d/0x310-----------这个软中断是timer
[176223.913386] [<ffffffff8109404d>] __do_softirq+0xfd/0x290
[176223.913390] [<ffffffff816c8afc>] call_softirq+0x1c/0x30
[176223.913394] [<ffffffff8102d435>] do_softirq+0x65/0xa0---------------------硬中断处理后,顺便处理软中断
[176223.913397] [<ffffffff81094495>] irq_exit+0x175/0x180---------------------硬中断结束
[176223.913400] [<ffffffff816c9e88>] smp_apic_timer_interrupt+0x48/0x60
[176223.913402] [<ffffffff816c6732>] apic_timer_interrupt+0x162/0x170---------硬中断开始
[176223.913403] <EOI> [<ffffffff81534357>] ? cpuidle_enter_state+0x57/0xd0
[176223.913410] [<ffffffff815344ae>] cpuidle_idle_call+0xde/0x230
[176223.913414] [<ffffffff81034f8e>] arch_cpu_idle+0xe/0x40
[176223.913420] [<ffffffff810edc4a>] cpu_startup_entry+0x14a/0x1c0
[176223.913423] [<ffffffff81052222>] start_secondary+0x1f2/0x270
[176223.913425] ---[ end trace 30e7271cf4a53655 ]---
[176223.913430] ixgbe ::00.0 eth4: Fake Tx hang detected with timeout of seconds
[176224.918915] ixgbe ::00.1 eth5: Fake Tx hang detected with timeout of seconds
[176224.918917] ixgbe :af:00.1 eth7: Fake Tx hang detected with timeout of seconds
[176224.918948] ixgbe :af:00.0 eth6: Fake Tx hang detected with timeout of seconds
[176224.934872] ixgbe ::00.1 eth1: Fake Tx hang detected with timeout of seconds
[176226.403293] hrtimer_gaq_time = , soft_irq_time = , cpu =
[176233.921764] ixgbe ::00.0 eth4: Fake Tx hang detected with timeout of seconds
[176234.911438] ixgbe :af:00.1 eth7: Fake Tx hang detected with timeout of seconds
[176234.911441] ixgbe ::00.1 eth5: Fake Tx hang detected with timeout of seconds
[176234.911474] ixgbe :af:00.0 eth6: Fake Tx hang detected with timeout of seconds
[176234.943364] ixgbe ::00.1 eth1: Fake Tx hang detected with timeout of seconds
[176237.664127] hrtimer_gaq_time = , soft_irq_time = , cpu =

如果只盯着这个堆栈看,可以看出,网卡的 dev_watchdog 函数检测到了eth4的queue 5 出现了 trans_timeout。

超时的检测周期,不同的设备是不一样的,intel的ixgbe对应的超时时间是 ixgbe_main.c 中设置的

netdev->watchdog_timeo =  * HZ;

检测的原理就是,每当发包成功的时候,设置 txq->trans_start ,如果这个值在timer到期检测的时候,和当前时间相差 一个超时周期(默认是5s,各种驱动可能不同),则认为出现发送

超时。依赖于定时器软中断,检测的对象是处于running状态的网卡已经处于stop状态的发送队列,话说网卡如果没有running,检测也没有意义。

static inline netdev_tx_t netdev_start_xmit(struct sk_buff *skb, struct net_device *dev,
struct netdev_queue *txq, bool more)
{
const struct net_device_ops *ops = dev->netdev_ops;
int rc;
/*__netdev_start_xmit 里面就完全是使用driver 的ops去发包了,其实到此为止,一个skb已经从netdevice层送到driver层了,接下来会等待driver的返回*/
rc = __netdev_start_xmit(ops, skb, dev, more);
if (rc == NETDEV_TX_OK)
txq_trans_update(txq); return rc;
}
static inline void txq_trans_update(struct netdev_queue *txq)
{
if (txq->xmit_lock_owner != -)
txq->trans_start = jiffies;---------------------更新当前发送队列txq的最后发送时间
}

ixgbe驱动会检测是否pending,也就是有的tx中的ring没变动了,那么打印warning。

接下来,又有一个堆栈:

[176242.505583] NMI watchdog: BUG: soft lockup - CPU# stuck for 22s! [kthread_send/:]-----------注意这个时候是cpu9
[176242.506532] Modules linked in: witdriver(OE) mysendmsg(OE) fuse tipc(OE) ossmod(OE) iptable_filter mptctl mptbase bonding dm_mirror dm_region_hash dm_log dm_mod iTCO_wdt iTCO_vendor_support skx_edac edac_core intel_powerclamp coretemp intel_rapl iosf_mbi kvm_intel kvm irqbypass crc32_pclmul ghash_clmulni_intel aesni_intel lrw gf128mul glue_helper ablk_helper cryptd pcspkr joydev ses enclosure sg mei_me mei shpchp lpc_ich i2c_i801 wmi ipmi_si ipmi_devintf ipmi_msghandler nfit libnvdimm acpi_power_meter acpi_cpufreq acpi_pad tcp_bbr sch_fq binfmt_misc ip_tables ext4 mbcache jbd2 raid1 sd_mod crc_t10dif crct10dif_generic ast i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm drm crct10dif_pclmul crct10dif_common crc32c_intel ahci libahci libata ixgbe(OE) i40e(OE) mpt3sas(OE)
[176242.506588] ptp raid_class pps_core scsi_transport_sas i2c_core dca [last unloaded: witdriver]
[176242.506597] CPU: PID: Comm: kthread_send/ Tainted: G W OE ------------ 3.10.-693.21..el7.x86_64 #
[176242.506599] Hardware name: ZTE ZXCDN/SC621DI-16F, BIOS .0b //
[176242.506601] task: ffff88290f7ddee0 ti: ffff882b680d0000 task.ti: ffff882b680d0000
[176242.506603] RIP: :[<ffffffff811005ce>] [<ffffffff811005ce>] native_queued_spin_lock_slowpath+0x1ce/0x200
[176242.506610] RSP: :ffff882fbe843dc0 EFLAGS:
[176242.506611] RAX: RBX: ffff882fbe843d50 RCX:
[176242.506613] RDX: RSI: RDI: ffff882fb80a0bc0-------大家都在抢的锁
[176242.506614] RBP: ffff882fbe843dc0 R08: R09: ffff8801363f4000
[176242.506616] R10: R11: ffff882fbe843da8 R12: ffff882fbe843d38
[176242.506617] R13: ffffffff816c6732 R14: ffff882fbe843dc0 R15: ffff882fb80a0b40
[176242.506619] FS: () GS:ffff882fbe840000() knlGS:
[176242.506621] CS: DS: ES: CR0:
[176242.506622] CR2: 00007fd86fd46316 CR3: 0000000001a0a000 CR4: 00000000003607e0
[176242.506624] DR0: DR1: DR2:
[176242.506626] DR3: DR6: 00000000fffe0ff0 DR7:
[176242.506627] Call Trace:
[176242.506629] <IRQ>
[176242.506630]
[176242.506635] [<ffffffff816adeee>] queued_spin_lock_slowpath+0xb/0xf
[176242.506640] [<ffffffff816bb080>] _raw_spin_lock+0x20/0x30
[176242.506645] [<ffffffff815bca52>] dev_watchdog+0x72/0x260-----------------------同上分析,不过这次是拿不到锁
[176242.506649] [<ffffffff815bc9e0>] ? dev_deactivate_queue.constprop.+0x60/0x60
[176242.506653] [<ffffffff8109a9c8>] call_timer_fn+0x38/0x110
[176242.506655] [<ffffffff815bc9e0>] ? dev_deactivate_queue.constprop.+0x60/0x60
[176242.506658] [<ffffffff8109ceed>] run_timer_softirq+0x22d/0x310
[176242.506663] [<ffffffff8109404d>] __do_softirq+0xfd/0x290
[176242.506667] [<ffffffff816c8afc>] call_softirq+0x1c/0x30
[176242.506672] [<ffffffff8102d435>] do_softirq+0x65/0xa0
[176242.506675] [<ffffffff81094495>] irq_exit+0x175/0x180
[176242.506679] [<ffffffff816c9e88>] smp_apic_timer_interrupt+0x48/0x60
[176242.506682] [<ffffffff816c6732>] apic_timer_interrupt+0x162/0x170----------------被硬中断打断
[176242.506684] <EOI>

[176242.506702] [<ffffffffc01299e3>] ? ixgbe_xmit_frame_ring+0x53/0xf30 [ixgbe]
[176242.506710] [<ffffffffc012a918>] ixgbe_xmit_frame+0x58/0xd0 [ixgbe]
[176242.506715] [<ffffffffc043b63c>] wit_send_tasklet+0x73c/0xae0 [witdriver]
[176242.506719] [<ffffffffc043ba95>] wit_kthread_xmit_fn+0xb5/0x150 [witdriver]----------我们的内核线程kthread_send调用的发包函数
[176242.506723] [<ffffffffc043b9e0>] ? wit_send_tasklet+0xae0/0xae0 [witdriver]
[176242.506726] [<ffffffff810b5241>] kthread+0xd1/0xe0
[176242.506729] [<ffffffff810b5170>] ? insert_kthread_work+0x40/0x40
[176242.506733] [<ffffffff816c5577>] ret_from_fork+0x77/0xb0
[176242.506736] [<ffffffff810b5170>] ? insert_kthread_work+0x40/0x40

分析这个堆栈,dev_watchdog 这次拿不到锁了,已经持续了22s,走查代码,它需要哪一把锁呢?

etif_tx_lock(dev);
static inline void netif_tx_lock(struct net_device *dev)
{
unsigned int i;
int cpu; spin_lock(&dev->tx_global_lock);
cpu = smp_processor_id();
for (i = ; i < dev->num_tx_queues; i++) {
struct netdev_queue *txq = netdev_get_tx_queue(dev, i); /* We are the only thread of execution doing a
* freeze, but we have to grab the _xmit_lock in
* order to synchronize with threads which are in
* the ->hard_start_xmit() handler and already
* checked the frozen bit.
*/
__netif_tx_lock(txq, cpu);
set_bit(__QUEUE_STATE_FROZEN, &txq->state);
__netif_tx_unlock(txq);
}
}

那这把锁被谁拿了呢?被 wit_kthread_xmit_fn 函数拿了,因为我们正在发包啊。

也就是说,我们的内核线程发包的时候,拿了锁,结果被中断,然后硬中断处理dev_watchdog的时候,也要拿这把锁,死锁了。

接下来,又引发其他cpu死锁:(每次进入_raw_spin_lock,rdi中必然存放的就是锁,x86反汇编看的话确实是rdi,其他架构不是如此)

[176246.611936] NMI watchdog: BUG: soft lockup - CPU# stuck for 22s! [a.out:]-------------------------------cpu25
[176246.612901] Modules linked in: witdriver(OE) mysendmsg(OE) fuse tipc(OE) ossmod(OE) iptable_filter mptctl mptbase bonding dm_mirror dm_region_hash dm_log dm_mod iTCO_wdt iTCO_vendor_support skx_edac edac_core intel_powerclamp coretemp intel_rapl iosf_mbi kvm_intel kvm irqbypass crc32_pclmul ghash_clmulni_intel aesni_intel lrw gf128mul glue_helper ablk_helper cryptd pcspkr joydev ses enclosure sg mei_me mei shpchp lpc_ich i2c_i801 wmi ipmi_si ipmi_devintf ipmi_msghandler nfit libnvdimm acpi_power_meter acpi_cpufreq acpi_pad tcp_bbr sch_fq binfmt_misc ip_tables ext4 mbcache jbd2 raid1 sd_mod crc_t10dif crct10dif_generic ast i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm drm crct10dif_pclmul crct10dif_common crc32c_intel ahci libahci libata ixgbe(OE) i40e(OE) mpt3sas(OE)
[176246.612961] ptp raid_class pps_core scsi_transport_sas i2c_core dca [last unloaded: witdriver]
[176246.612969] CPU: PID: Comm: a.out Tainted: G W OEL ------------ 3.10.-693.21..el7.x86_64 #
[176246.612970] Hardware name: ZTE ZXCDN/SC621DI-16F, BIOS .0b //
[176246.612973] task: ffff882ba14a0000 ti: ffff882ba92c8000 task.ti: ffff882ba92c8000
[176246.612974] RIP: :[<ffffffff81100556>] [<ffffffff81100556>] native_queued_spin_lock_slowpath+0x156/0x200
[176246.612982] RSP: :ffff882ba92cb978 EFLAGS:
[176246.612983] RAX: RBX: 0000090190134ba9 RCX: 0000000000c90000
[176246.612985] RDX: 0000000000c90101 RSI: RDI: ffff882fb80a0bc0------------大家都在抢的香饽饽存放在此,就是这把锁
[176246.612986] RBP: ffff882ba92cb978 R08: ffff882fbe959700 R09:
[176246.612988] R10: R11: ffffea017c3e5580 R12: ffff882c18a85c00
[176246.612989] R13: 00000000000005dc R14: ffff882ba2091100 R15: ffffffff811e63d1
[176246.612991] FS: 00007fbf25f9b700() GS:ffff882fbe940000() knlGS:
[176246.612993] CS: DS: ES: CR0:
[176246.612995] CR2: 0000000000c79000 CR3: 000000593a2ec000 CR4: 00000000003607e0
[176246.612996] DR0: DR1: DR2:
[176246.612998] DR3: DR6: 00000000fffe0ff0 DR7:
[176246.612999] Call Trace:
[176246.613006] [<ffffffff816adeee>] queued_spin_lock_slowpath+0xb/0xf
[176246.613011] [<ffffffff816bb080>] _raw_spin_lock+0x20/0x30
[176246.613015] [<ffffffff815bcd7f>] sch_direct_xmit+0x13f/0x240------------qdisc中sys调用发包
[176246.613017] [<ffffffff815bcf15>] __qdisc_run+0x95/0x1c0
[176246.613022] [<ffffffff81596989>] __dev_queue_xmit+0x2c9/0x550-----------这个是实际物理网卡的
[176246.613025] [<ffffffff81596c20>] dev_queue_xmit+0x10/0x20
[176246.613032] [<ffffffffc03abbe2>] bond_dev_queue_xmit+0x32/0x80 [bonding]
[176246.613036] [<ffffffffc03ad7be>] bond_start_xmit+0x1be/0x420 [bonding]
[176246.613039] [<ffffffff81593bc0>] dev_hard_start_xmit+0x90/0x1a0
[176246.613041] [<ffffffff81596b08>] __dev_queue_xmit+0x448/0x550-----------这个是bond的
[176246.613044] [<ffffffff81596c20>] dev_queue_xmit+0x10/0x20
[176246.613048] [<ffffffff815dd8f6>] ip_finish_output+0x546/0x7a0
[176246.613050] [<ffffffff815dde53>] ip_output+0x73/0xe0
[176246.613053] [<ffffffff815dba46>] ? __ip_local_out_sk+0xf6/0x100
[176246.613055] [<ffffffff815dba87>] ip_local_out_sk+0x37/0x40
[176246.613058] [<ffffffff815de8a6>] ip_send_skb+0x16/0x50
[176246.613062] [<ffffffff81606a9c>] udp_send_skb+0xac/0x2b0
[176246.613065] [<ffffffff81606cde>] udp_push_pending_frames+0x3e/0x60
[176246.613068] [<ffffffff81608b19>] udp_sendpage+0x119/0x1c0
[176246.613071] [<ffffffff81615490>] inet_sendpage+0x70/0xe0
[176246.613075] [<ffffffff8157613e>] kernel_sendpage+0x1e/0x30
[176246.613079] [<ffffffffc04363a8>] sendfile_slowpath_2+0x1a8/0x1f0 [witdriver]
[176246.613084] [<ffffffffc04458a6>] sys_mycall+0x776/0x8f0 [witdriver]
[176246.613090] [<ffffffff816c5715>] system_call_fastpath+0x1c/0x21
[176246.613091] Code: 8b 4d c9 0f 8b 0f b7 c2 c0 f8 eb 1a 2e 0f 1f c0 0c f3 <8b> 0f b7 c2 f8 f0 be eb 0f 1f

由于我们拿的是dev的锁,在没开启抢占的情况下不调度出去,但也并没有关中断,这样其他cpu在系统调用中要发包,也会去尝试拿这把锁,好吧,你也死锁了,等着吧。

可以想象,后续其他cpu要拿这把锁的话,大家都会挂,一个cpu的softlock导致其他cpu全挂,只要你这个cpu来拿那锁就会如此。

由于我们拿的是spin_lock,并没有关中断,所以它还可以响应中断,看如下堆栈就明白,最早打印网卡异常的9号cpu,堆栈在死的时候是如下这样的:

crash> bt
PID: TASK: ffff88290f7ddee0 CPU: COMMAND: "kthread_send/9"
# [ffff882fbe843a70] machine_kexec at ffffffff8105d77b
# [ffff882fbe843ad0] __crash_kexec at ffffffff8110aca2
# [ffff882fbe843ba0] panic at ffffffff816ad52f
# [ffff882fbe843c20] watchdog_timer_fn at ffffffff81135a51----------------------------hardlock检测中hrtimer的回调
# [ffff882fbe843c58] __hrtimer_run_queues at ffffffff810b93a6
# [ffff882fbe843cb0] hrtimer_interrupt at ffffffff810b993f
# [ffff882fbe843cf8] local_apic_timer_interrupt at ffffffff8105467b
# [ffff882fbe843d10] smp_apic_timer_interrupt at ffffffff816c9e83
# [ffff882fbe843d28] apic_timer_interrupt at ffffffff816c6732--------------------------死之前又增加的堆栈,这个是硬中断
# [ffff882fbe843dc8] queued_spin_lock_slowpath at ffffffff816adeee---------------------一开始打印hung的堆栈,在自旋
# [ffff882fbe843dd8] _raw_spin_lock at ffffffff816bb080
# [ffff882fbe843de8] dev_watchdog at ffffffff815bca52
# [ffff882fbe843e28] call_timer_fn at ffffffff8109a9c8
# [ffff882fbe843e60] run_timer_softirq at ffffffff8109ceed
# [ffff882fbe843ed8] __do_softirq at ffffffff8109404d
# [ffff882fbe843f48] call_softirq at ffffffff816c8afc
# [ffff882fbe843f60] do_softirq at ffffffff8102d435
# [ffff882fbe843f80] irq_exit at ffffffff81094495
# [ffff882fbe843f98] smp_apic_timer_interrupt at ffffffff816c9e88
# [ffff882fbe843fb0] apic_timer_interrupt at ffffffff816c6732
--- <IRQ stack> ---
# [ffff882b680d3c28] apic_timer_interrupt at ffffffff816c6732
[exception RIP: ixgbe_xmit_frame_ring+]
RIP: ffffffffc01299e3 RSP: ffff882b680d3cd0 RFLAGS:
RAX: RBX: RCX: 000000000000403d
RDX: ffff882fb9331c00 RSI: ffff8828d7b8fac0 RDI:
RBP: ffff882b680d3d48 R8: R9: 0000a0a5447b9d78
R10: ffff8828c6e84f00 R11: 000000002b3000b8 R12: ffff8828c0291b00
R13: R14: R15: ffff882b680d3cc0
ORIG_RAX: ffffffffffffff10 CS: SS:
# [ffff882b680d3d50] ixgbe_xmit_frame at ffffffffc012a918 [ixgbe]
# [ffff882b680d3d80] wit_send_tasklet at ffffffffc043b63c [witdriver]
# [ffff882b680d3e78] wit_kthread_xmit_fn at ffffffffc043ba95 [witdriver]
# [ffff882b680d3ec8] kthread at ffffffff810b5241
# [ffff882b680d3f50] ret_from_fork at ffffffff816c5577

总结:

1、解决办法很简单,就是在 wit_kthread_xmit_fn 函数中,加了一个关闭软中断就行,因为就是软中断和sys拿锁冲突。

2、分析软锁,最好从dmesg中开始分析,那个时候时间还早,会按时间顺序来打印堆栈,比起直接crash来分析要快一些,特别是在对自己模块代码比较熟悉的情况下。

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