最近的修改导致解析DNS耗尽CPU

[darren]

Tasks: 179 total,   1 running, 178 sleeping,   0 stopped,   0 zombie
%Cpu0  :  92.1/7.9   100[                                                                                               ]     %Cpu1  :  96.1/2.9    99[                                                                                               ]
%Cpu2  :  97.1/2.0    99[                                                                                               ]     %Cpu3  :  96.0/4.0   100[                                                                                               ]
MiB Mem : 14.4/15931.7  [||||||||||||||                                                                                 ]
MiB Swap:  0.0/0.0      [                                                                                               ]

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND                                                                                                                                                                           
 328020 root      20   0 5800.2m  74.9m  17.0m S 364.4   0.5 675:58.01 /usr/bin/v2ray -config /etc/v2/default.json           

Samples: 284K of event 'cycles', 4000 Hz, Event count (approx.): 27101695767 lost: 0/0 drop: 0/0                                                                                                                                                         
Overhead  Shared Object       Symbol                                                                                                                                                                                                                     
  17.27%  v2                  [.] runtime.selectgo                                                                                                                                                                                                       
  15.02%  v2                  [.] github.com/v2fly/v2ray-core/v4/app/dns.(*DoHNameServer).findIPsForDomain                                                                                                                                               
   7.22%  v2                  [.] runtime.unlock2                                                                                                                                                                                                        
   6.92%  v2                  [.] context.(*cancelCtx).Done                                                                                                                                                                                              
   6.81%  v2                  [.] runtime.lock2                                                                                                                                                                                                          
   6.81%  [vdso]              [.] 0x0000000000000695                                                                                                                                                                                                     
   4.63%  v2                  [.] runtime.mapaccess2_faststr                                                                                                                                                                                             
   4.34%  [vdso]              [.] __vdso_clock_gettime                                                                                                                                                                                                   
   3.11%  v2                  [.] runtime.sellock                                                                                                                                                                                                        
   3.00%  v2                  [.] runtime.selunlock                                                                                                                                                                                                      
   2.70%  v2                  [.] runtime.walltime1                                                                                                                                                                                                      
   2.70%  v2                  [.] github.com/v2fly/v2ray-core/v4/app/dns.(*DoHNameServer).QueryIP                                                                                                                                                        
   2.53%  v2                  [.] runtime.nanotime1                                                                                                                                                                                                      
   2.45%  v2                  [.] aeshashbody                                                                                                                                                                                                            
   2.36%  v2                  [.] github.com/v2fly/v2ray-core/v4/app/dns.(*IPRecord).getIPs                                                                                                                                                              
   1.52%  v2                  [.] time.now                                                                                                                                                                                                               
   1.42%  v2                  [.] memeqbody                                                                                                                                                                                                              
   1.21%  v2                  [.] time.Now                                                                                                                                                                                                               
   0.75%  v2                  [.] runtime.typedslicecopy                                                                                                                                                                                                 
   0.70%  v2                  [.] context.(*timerCtx).Done                                                                                                                                                                                               
   0.61%  v2                  [.] time.Time.Before                                                                                                                                                                                                       
   0.32%  v2                  [.] runtime.strhash                                                                                                                                                                                                        
   0.27%  [vdso]              [.] 0x0000000000000698     

版本： 639148d

[Loyalsoldier]

分别试一试这三个版本：
a783cd5
73470e8
ecaf597

[darren]

测试结果：

a783cd5 bad
73470e8 bad
ecaf597 good

50bcb68 版本的profile结果

发现出现CPU被全部占用的时候，可能是遇到了不存在AAAA记录的域名，反复执行以下代码

v2ray-core/app/dns/nameserver_doh.go

Lines 373 to 384 in 50bcb68

	for {
	ips, err := s.findIPsForDomain(fqdn, option)
	if err != errRecordNotFound {
	return ips, err
	}
	select {
	case <-ctx.Done():
	return nil, ctx.Err()
	case <-done:
	}
	}

记录日志跟踪了一下:

        i := 0
	for {
                i++
		ips, err := s.findIPsForDomain(fqdn, option)
	        log.Printf("RESOLVE: %s %d", fqdn, i)
	        if err != errRecordNotFound {
			return ips, err
		}

		select {
		case <-ctx.Done():
			return nil, ctx.Err()
		case <-done:
		}
	}

记录到以下日志:

 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19698
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19699
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 17996
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19700
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 17997
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19701
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 17998
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19702
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 17999
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 18000
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 18001
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19703
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19704
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 18002
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19705
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 18003
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 18004
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19706
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 18005
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19707
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19708
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 18006
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19709
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 18007
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19710
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19711
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 18008
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 18009
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19712
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19713
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19714
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19715
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69275
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19716
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19717
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69276
 2021/08/29 04:54:20 RESOLVE: vortex.data.microsoft.com. 19718
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69277
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69278
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69279
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69280
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69281
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69282
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69283
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69284
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69285
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69286
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69287
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69288
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69289
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69290
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69291
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69292
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69293
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69294
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69295
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69296
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69297
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69298
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69299
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69300
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69301
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 4259
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69302
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 4260
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69303
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 4261
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69304
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 4262
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69305
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69306
 2021/08/29 04:54:20 RESOLVE: alive.github.com. 69307

解析 alive.github.com 在一秒内这段代码被执行了 2,026,539次

[Loyalsoldier]

I think 46fa8f7 has fixed the problem.