lockosthread.go

     1  // Copyright 2017 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package main
     6  
     7  import (
     8  	"os"
     9  	"runtime"
    10  	"sync"
    11  	"time"
    12  )
    13  
    14  var mainTID int
    15  
    16  func init() {
    17  	registerInit("LockOSThreadMain", func() {
    18  		// init is guaranteed to run on the main thread.
    19  		mainTID = gettid()
    20  	})
    21  	register("LockOSThreadMain", LockOSThreadMain)
    22  
    23  	registerInit("LockOSThreadAlt", func() {
    24  		// Lock the OS thread now so main runs on the main thread.
    25  		runtime.LockOSThread()
    26  	})
    27  	register("LockOSThreadAlt", LockOSThreadAlt)
    28  
    29  	registerInit("LockOSThreadAvoidsStatePropagation", func() {
    30  		// Lock the OS thread now so main runs on the main thread.
    31  		runtime.LockOSThread()
    32  	})
    33  	register("LockOSThreadAvoidsStatePropagation", LockOSThreadAvoidsStatePropagation)
    34  	register("LockOSThreadTemplateThreadRace", LockOSThreadTemplateThreadRace)
    35  }
    36  
    37  func LockOSThreadMain() {
    38  	// gettid only works on Linux, so on other platforms this just
    39  	// checks that the runtime doesn't do anything terrible.
    40  
    41  	// This requires GOMAXPROCS=1 from the beginning to reliably
    42  	// start a goroutine on the main thread.
    43  	if runtime.GOMAXPROCS(-1) != 1 {
    44  		println("requires GOMAXPROCS=1")
    45  		os.Exit(1)
    46  	}
    47  
    48  	ready := make(chan bool, 1)
    49  	go func() {
    50  		// Because GOMAXPROCS=1, this *should* be on the main
    51  		// thread. Stay there.
    52  		runtime.LockOSThread()
    53  		if mainTID != 0 && gettid() != mainTID {
    54  			println("failed to start goroutine on main thread")
    55  			os.Exit(1)
    56  		}
    57  		// Exit with the thread locked, which should exit the
    58  		// main thread.
    59  		ready <- true
    60  	}()
    61  	<-ready
    62  	time.Sleep(1 * time.Millisecond)
    63  	// Check that this goroutine is still running on a different
    64  	// thread.
    65  	if mainTID != 0 && gettid() == mainTID {
    66  		println("goroutine migrated to locked thread")
    67  		os.Exit(1)
    68  	}
    69  	println("OK")
    70  }
    71  
    72  func LockOSThreadAlt() {
    73  	// This is running locked to the main OS thread.
    74  
    75  	var subTID int
    76  	ready := make(chan bool, 1)
    77  	go func() {
    78  		// This goroutine must be running on a new thread.
    79  		runtime.LockOSThread()
    80  		subTID = gettid()
    81  		ready <- true
    82  		// Exit with the thread locked.
    83  	}()
    84  	<-ready
    85  	runtime.UnlockOSThread()
    86  	for i := 0; i < 100; i++ {
    87  		time.Sleep(1 * time.Millisecond)
    88  		// Check that this goroutine is running on a different thread.
    89  		if subTID != 0 && gettid() == subTID {
    90  			println("locked thread reused")
    91  			os.Exit(1)
    92  		}
    93  		exists, supported, err := tidExists(subTID)
    94  		if err != nil {
    95  			println("error:", err.Error())
    96  			return
    97  		}
    98  		if !supported || !exists {
    99  			goto ok
   100  		}
   101  	}
   102  	println("sub thread", subTID, "still running")
   103  	return
   104  ok:
   105  	println("OK")
   106  }
   107  
   108  func LockOSThreadAvoidsStatePropagation() {
   109  	// This test is similar to LockOSThreadAlt in that it will detect if a thread
   110  	// which should have died is still running. However, rather than do this with
   111  	// thread IDs, it does this by unsharing state on that thread. This way, it
   112  	// also detects whether new threads were cloned from the dead thread, and not
   113  	// from a clean thread. Cloning from a locked thread is undesirable since
   114  	// cloned threads will inherit potentially unwanted OS state.
   115  	//
   116  	// unshareFs, getcwd, and chdir("/tmp") are only guaranteed to work on
   117  	// Linux, so on other platforms this just checks that the runtime doesn't
   118  	// do anything terrible.
   119  	//
   120  	// This is running locked to the main OS thread.
   121  
   122  	// GOMAXPROCS=1 makes this fail much more reliably if a tainted thread is
   123  	// cloned from.
   124  	if runtime.GOMAXPROCS(-1) != 1 {
   125  		println("requires GOMAXPROCS=1")
   126  		os.Exit(1)
   127  	}
   128  
   129  	if err := chdir("/"); err != nil {
   130  		println("failed to chdir:", err.Error())
   131  		os.Exit(1)
   132  	}
   133  	// On systems other than Linux, cwd == "".
   134  	cwd, err := getcwd()
   135  	if err != nil {
   136  		println("failed to get cwd:", err.Error())
   137  		os.Exit(1)
   138  	}
   139  	if cwd != "" && cwd != "/" {
   140  		println("unexpected cwd", cwd, " wanted /")
   141  		os.Exit(1)
   142  	}
   143  
   144  	ready := make(chan bool, 1)
   145  	go func() {
   146  		// This goroutine must be running on a new thread.
   147  		runtime.LockOSThread()
   148  
   149  		// Unshare details about the FS, like the CWD, with
   150  		// the rest of the process on this thread.
   151  		// On systems other than Linux, this is a no-op.
   152  		if err := unshareFs(); err != nil {
   153  			if err == errNotPermitted {
   154  				println("unshare not permitted")
   155  				os.Exit(0)
   156  			}
   157  			println("failed to unshare fs:", err.Error())
   158  			os.Exit(1)
   159  		}
   160  		// Chdir to somewhere else on this thread.
   161  		// On systems other than Linux, this is a no-op.
   162  		if err := chdir(os.TempDir()); err != nil {
   163  			println("failed to chdir:", err.Error())
   164  			os.Exit(1)
   165  		}
   166  
   167  		// The state on this thread is now considered "tainted", but it
   168  		// should no longer be observable in any other context.
   169  
   170  		ready <- true
   171  		// Exit with the thread locked.
   172  	}()
   173  	<-ready
   174  
   175  	// Spawn yet another goroutine and lock it. Since GOMAXPROCS=1, if
   176  	// for some reason state from the (hopefully dead) locked thread above
   177  	// propagated into a newly created thread (via clone), or that thread
   178  	// is actually being re-used, then we should get scheduled on such a
   179  	// thread with high likelihood.
   180  	done := make(chan bool)
   181  	go func() {
   182  		runtime.LockOSThread()
   183  
   184  		// Get the CWD and check if this is the same as the main thread's
   185  		// CWD. Every thread should share the same CWD.
   186  		// On systems other than Linux, wd == "".
   187  		wd, err := getcwd()
   188  		if err != nil {
   189  			println("failed to get cwd:", err.Error())
   190  			os.Exit(1)
   191  		}
   192  		if wd != cwd {
   193  			println("bad state from old thread propagated after it should have died")
   194  			os.Exit(1)
   195  		}
   196  		<-done
   197  
   198  		runtime.UnlockOSThread()
   199  	}()
   200  	done <- true
   201  	runtime.UnlockOSThread()
   202  	println("OK")
   203  }
   204  
   205  func LockOSThreadTemplateThreadRace() {
   206  	// This test attempts to reproduce the race described in
   207  	// golang.org/issue/38931. To do so, we must have a stop-the-world
   208  	// (achieved via ReadMemStats) racing with two LockOSThread calls.
   209  	//
   210  	// While this test attempts to line up the timing, it is only expected
   211  	// to fail (and thus hang) around 2% of the time if the race is
   212  	// present.
   213  
   214  	// Ensure enough Ps to actually run everything in parallel. Though on
   215  	// <4 core machines, we are still at the whim of the kernel scheduler.
   216  	runtime.GOMAXPROCS(4)
   217  
   218  	go func() {
   219  		// Stop the world; race with LockOSThread below.
   220  		var m runtime.MemStats
   221  		for {
   222  			runtime.ReadMemStats(&m)
   223  		}
   224  	}()
   225  
   226  	// Try to synchronize both LockOSThreads.
   227  	start := time.Now().Add(10 * time.Millisecond)
   228  
   229  	var wg sync.WaitGroup
   230  	wg.Add(2)
   231  
   232  	for i := 0; i < 2; i++ {
   233  		go func() {
   234  			for time.Now().Before(start) {
   235  			}
   236  
   237  			// Add work to the local runq to trigger early startm
   238  			// in handoffp.
   239  			go func() {}()
   240  
   241  			runtime.LockOSThread()
   242  			runtime.Gosched() // add a preemption point.
   243  			wg.Done()
   244  		}()
   245  	}
   246  
   247  	wg.Wait()
   248  	// If both LockOSThreads completed then we did not hit the race.
   249  	println("OK")
   250  }
   251
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