File size: 1,915 Bytes
de452ad | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 | // Copyright 2025 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"runtime"
)
func init() {
register("mexitSTW", mexitSTW)
}
// Stress test for pp.oldm pointing to an exited M.
//
// If pp.oldm points to an exited M it should be ignored and another M used
// instead. To stress:
//
// 1. Start and exit many threads (thus setting oldm on some P).
// 2. Meanwhile, frequently stop the world.
//
// If procresize incorrect attempts to assign a P to an exited M, likely
// failure modes are:
//
// 1. Crash in startTheWorldWithSema attempting to access the M, if it is nil.
//
// 2. Memory corruption elsewhere after startTheWorldWithSema writes to the M,
// if it is not nil, but is freed and reused for another allocation.
//
// 3. Hang on a subsequent stop the world waiting for the P to stop, if the M
// object is valid, but the M is exited, because startTheWorldWithSema didn't
// actually wake anything to run the P. The P is _Pidle, but not in the pidle
// list, thus startTheWorldWithSema will wake for it to actively stop.
//
// For this to go wrong, an exited M must fail to clear mp.self and must leave
// the M on the sched.midle list.
//
// Similar to TraceSTW.
func mexitSTW() {
// Ensure we have multiple Ps, but not too many, as we want the
// runnable goroutines likely to run on Ps with oldm set.
runtime.GOMAXPROCS(4)
// Background busy work so there is always something runnable.
for i := range 2 {
go traceSTWTarget(i)
}
// Wait for children to start running.
ping.Store(1)
for pong[0].Load() != 1 {}
for pong[1].Load() != 1 {}
for range 100 {
// Exit a thread. The last P to run this will have it in oldm.
go func() {
runtime.LockOSThread()
}()
// STW
var ms runtime.MemStats
runtime.ReadMemStats(&ms)
}
stop.Store(true)
println("OK")
}
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