ff7cf2d4cd
Currently any thread that tries to get the attention of all Ps (e.g. stopTheWorldWithSema and forEachP) ends up in a non-preemptible state waiting to preempt another thread. Thing is, that other thread might also be in a non-preemptible state, trying to preempt the first thread, resulting in a deadlock. This is a general problem, but in practice it only boils down to one specific scenario: a thread in GC is blocked trying to preempt a goroutine to scan its stack while that goroutine is blocked in a non-preemptible state to get the attention of all Ps. There's currently a hack in a few places in the runtime to move the calling goroutine into _Gwaiting before it goes into a non-preemptible state to preempt other threads. This lets the GC scan its stack because the goroutine is trivially preemptible. The only restriction is that forEachP and stopTheWorldWithSema absolutely cannot reference the calling goroutine's stack. This is generally not necessary, so things are good. Anyway, to avoid exposing the details of this hack, this change creates a safer wrapper around forEachP (and then renames it to forEachP and the existing one to forEachPInternal) that performs the goroutine status change, just like stopTheWorld does. We're going to need to use this hack with forEachP in the new tracer, so this avoids propagating the hack further and leaves it as an implementation detail. Change-Id: I51f02e8d8e0a3172334d23787e31abefb8a129ab Reviewed-on: https://go-review.googlesource.com/c/go/+/533455 Auto-Submit: Michael Knyszek <mknyszek@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Michael Pratt <mpratt@google.com> |
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