1 // Copyright 2023 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 // Tests a G being created from within a syscall. 6 // 7 // Specifically, it tests a scenerio wherein a C 8 // thread is calling into Go, creating a goroutine in 9 // a syscall (in the tracer's model). The system is free 10 // to reuse thread IDs, so first a thread ID is used to 11 // call into Go, and then is used for a Go-created thread. 12 // 13 // This is a regression test. The trace parser didn't correctly 14 // model GoDestroySyscall as dropping its P (even if the runtime 15 // did). It turns out this is actually fine if all the threads 16 // in the trace have unique IDs, since the P just stays associated 17 // with an eternally dead thread, and it's stolen by some other 18 // thread later. But if thread IDs are reused, then the tracer 19 // gets confused when trying to advance events on the new thread. 20 // The now-dead thread which exited on a GoDestroySyscall still has 21 // its P associated and this transfers to the newly-live thread 22 // in the parser's state because they share a thread ID. 23 24 package main 25 26 import ( 27 "internal/trace/v2" 28 "internal/trace/v2/event/go122" 29 testgen "internal/trace/v2/internal/testgen/go122" 30 ) 31 32 func main() { 33 testgen.Main(gen) 34 } 35 36 func gen(t *testgen.Trace) { 37 g := t.Generation(1) 38 39 // A C thread calls into Go and acquires a P. It returns 40 // back to C, destroying the G. 41 b0 := g.Batch(trace.ThreadID(0), 0) 42 b0.Event("GoCreateSyscall", trace.GoID(4)) 43 b0.Event("GoSyscallEndBlocked") 44 b0.Event("ProcStatus", trace.ProcID(0), go122.ProcIdle) 45 b0.Event("ProcStart", trace.ProcID(0), testgen.Seq(1)) 46 b0.Event("GoStatus", trace.GoID(4), trace.NoThread, go122.GoRunnable) 47 b0.Event("GoStart", trace.GoID(4), testgen.Seq(1)) 48 b0.Event("GoSyscallBegin", testgen.Seq(2), testgen.NoStack) 49 b0.Event("GoDestroySyscall") 50 51 // A new Go-created thread with the same ID appears and 52 // starts running, then tries to steal the P from the 53 // first thread. The stealing is interesting because if 54 // the parser handles GoDestroySyscall wrong, then we 55 // have a self-steal here potentially that doesn't make 56 // sense. 57 b1 := g.Batch(trace.ThreadID(0), 0) 58 b1.Event("ProcStatus", trace.ProcID(1), go122.ProcIdle) 59 b1.Event("ProcStart", trace.ProcID(1), testgen.Seq(1)) 60 b1.Event("ProcSteal", trace.ProcID(0), testgen.Seq(3), trace.ThreadID(0)) 61 } 62