diff options
Diffstat (limited to 'src/runtime/proc.go')
| -rw-r--r-- | src/runtime/proc.go | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/src/runtime/proc.go b/src/runtime/proc.go index 9a252cfcf5..3cecd1a057 100644 --- a/src/runtime/proc.go +++ b/src/runtime/proc.go @@ -921,6 +921,35 @@ var freezing atomic.Bool // This function must not lock any mutexes. func freezetheworld() { freezing.Store(true) + if debug.dontfreezetheworld > 0 { + // Don't prempt Ps to stop goroutines. That will perturb + // scheduler state, making debugging more difficult. Instead, + // allow goroutines to continue execution. + // + // fatalpanic will tracebackothers to trace all goroutines. It + // is unsafe to trace a running goroutine, so tracebackothers + // will skip running goroutines. That is OK and expected, we + // expect users of dontfreezetheworld to use core files anyway. + // + // However, allowing the scheduler to continue running free + // introduces a race: a goroutine may be stopped when + // tracebackothers checks its status, and then start running + // later when we are in the middle of traceback, potentially + // causing a crash. + // + // To mitigate this, when an M naturally enters the scheduler, + // schedule checks if freezing is set and if so stops + // execution. This guarantees that while Gs can transition from + // running to stopped, they can never transition from stopped + // to running. + // + // The sleep here allows racing Ms that missed freezing and are + // about to run a G to complete the transition to running + // before we start traceback. + usleep(1000) + return + } + // stopwait and preemption requests can be lost // due to races with concurrently executing threads, // so try several times @@ -3552,6 +3581,18 @@ top: gp, inheritTime, tryWakeP := findRunnable() // blocks until work is available + if debug.dontfreezetheworld > 0 && freezing.Load() { + // See comment in freezetheworld. We don't want to perturb + // scheduler state, so we didn't gcstopm in findRunnable, but + // also don't want to allow new goroutines to run. + // + // Deadlock here rather than in the findRunnable loop so if + // findRunnable is stuck in a loop we don't perturb that + // either. + lock(&deadlock) + lock(&deadlock) + } + // This thread is going to run a goroutine and is not spinning anymore, // so if it was marked as spinning we need to reset it now and potentially // start a new spinning M. |