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 := tidExists(subTID)
    94  		if !supported || !exists {
    95  			goto ok
    96  		}
    97  	}
    98  	println("sub thread", subTID, "still running")
    99  	return
   100  ok:
   101  	println("OK")
   102  }
   103  
   104  func LockOSThreadAvoidsStatePropagation() {
   105  	// This test is similar to LockOSThreadAlt in that it will detect if a thread
   106  	// which should have died is still running. However, rather than do this with
   107  	// thread IDs, it does this by unsharing state on that thread. This way, it
   108  	// also detects whether new threads were cloned from the dead thread, and not
   109  	// from a clean thread. Cloning from a locked thread is undesirable since
   110  	// cloned threads will inherit potentially unwanted OS state.
   111  	//
   112  	// unshareFs, getcwd, and chdir("/tmp") are only guaranteed to work on
   113  	// Linux, so on other platforms this just checks that the runtime doesn't
   114  	// do anything terrible.
   115  	//
   116  	// This is running locked to the main OS thread.
   117  
   118  	// GOMAXPROCS=1 makes this fail much more reliably if a tainted thread is
   119  	// cloned from.
   120  	if runtime.GOMAXPROCS(-1) != 1 {
   121  		println("requires GOMAXPROCS=1")
   122  		os.Exit(1)
   123  	}
   124  
   125  	if err := chdir("/"); err != nil {
   126  		println("failed to chdir:", err.Error())
   127  		os.Exit(1)
   128  	}
   129  	// On systems other than Linux, cwd == "".
   130  	cwd, err := getcwd()
   131  	if err != nil {
   132  		println("failed to get cwd:", err.Error())
   133  		os.Exit(1)
   134  	}
   135  	if cwd != "" && cwd != "/" {
   136  		println("unexpected cwd", cwd, " wanted /")
   137  		os.Exit(1)
   138  	}
   139  
   140  	ready := make(chan bool, 1)
   141  	go func() {
   142  		// This goroutine must be running on a new thread.
   143  		runtime.LockOSThread()
   144  
   145  		// Unshare details about the FS, like the CWD, with
   146  		// the rest of the process on this thread.
   147  		// On systems other than Linux, this is a no-op.
   148  		if err := unshareFs(); err != nil {
   149  			if err == errNotPermitted {
   150  				println("unshare not permitted")
   151  				os.Exit(0)
   152  			}
   153  			println("failed to unshare fs:", err.Error())
   154  			os.Exit(1)
   155  		}
   156  		// Chdir to somewhere else on this thread.
   157  		// On systems other than Linux, this is a no-op.
   158  		if err := chdir("/tmp"); err != nil {
   159  			println("failed to chdir:", err.Error())
   160  			os.Exit(1)
   161  		}
   162  
   163  		// The state on this thread is now considered "tainted", but it
   164  		// should no longer be observable in any other context.
   165  
   166  		ready <- true
   167  		// Exit with the thread locked.
   168  	}()
   169  	<-ready
   170  
   171  	// Spawn yet another goroutine and lock it. Since GOMAXPROCS=1, if
   172  	// for some reason state from the (hopefully dead) locked thread above
   173  	// propagated into a newly created thread (via clone), or that thread
   174  	// is actually being re-used, then we should get scheduled on such a
   175  	// thread with high likelihood.
   176  	done := make(chan bool)
   177  	go func() {
   178  		runtime.LockOSThread()
   179  
   180  		// Get the CWD and check if this is the same as the main thread's
   181  		// CWD. Every thread should share the same CWD.
   182  		// On systems other than Linux, wd == "".
   183  		wd, err := getcwd()
   184  		if err != nil {
   185  			println("failed to get cwd:", err.Error())
   186  			os.Exit(1)
   187  		}
   188  		if wd != cwd {
   189  			println("bad state from old thread propagated after it should have died")
   190  			os.Exit(1)
   191  		}
   192  		<-done
   193  
   194  		runtime.UnlockOSThread()
   195  	}()
   196  	done <- true
   197  	runtime.UnlockOSThread()
   198  	println("OK")
   199  }
   200  
   201  func LockOSThreadTemplateThreadRace() {
   202  	// This test attempts to reproduce the race described in
   203  	// golang.org/issue/38931. To do so, we must have a stop-the-world
   204  	// (achieved via ReadMemStats) racing with two LockOSThread calls.
   205  	//
   206  	// While this test attempts to line up the timing, it is only expected
   207  	// to fail (and thus hang) around 2% of the time if the race is
   208  	// present.
   209  
   210  	// Ensure enough Ps to actually run everything in parallel. Though on
   211  	// <4 core machines, we are still at the whim of the kernel scheduler.
   212  	runtime.GOMAXPROCS(4)
   213  
   214  	go func() {
   215  		// Stop the world; race with LockOSThread below.
   216  		var m runtime.MemStats
   217  		for {
   218  			runtime.ReadMemStats(&m)
   219  		}
   220  	}()
   221  
   222  	// Try to synchronize both LockOSThreads.
   223  	start := time.Now().Add(10 * time.Millisecond)
   224  
   225  	var wg sync.WaitGroup
   226  	wg.Add(2)
   227  
   228  	for i := 0; i < 2; i++ {
   229  		go func() {
   230  			for time.Now().Before(start) {
   231  			}
   232  
   233  			// Add work to the local runq to trigger early startm
   234  			// in handoffp.
   235  			go func() {}()
   236  
   237  			runtime.LockOSThread()
   238  			runtime.Gosched() // add a preemption point.
   239  			wg.Done()
   240  		}()
   241  	}
   242  
   243  	wg.Wait()
   244  	// If both LockOSThreads completed then we did not hit the race.
   245  	println("OK")
   246  }
   247
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