ca1d2ead5d
Some of the new experimental events added have a problem in that they might be emitted during stack growth. This is, to my knowledge, the only restriction on the tracer, because the tracer otherwise prevents preemption, avoids allocation, and avoids write barriers. However, the stack can grow from within the tracer. This leads to tracing-during-tracing which can result in lost buffers and broken event streams. (There's a debug mode to get a nice error message, but it's disabled by default.) This change resolves the problem by skipping writing out these new events. This results in the new events sometimes being broken (alloc without a free, free without an alloc) but for now that's OK. Before the freeze begins we just want to fix broken tests; tools interpreting these events will be totally in-house to begin with, and if they have to be a little bit smarter about missing information, that's OK. In the future we'll have a more robust fix for this, but it appears that it's going to require making the tracer fully reentrant. (This is not too hard; either we force flushing all buffers when going reentrant (which is actually somewhat subtle with respect to event ordering) or we isolate down just the actual event writing to be atomic with respect to stack growth. Both are just bigger changes on shared codepaths that are scary to land this late in the release cycle.) Fixes #67379. Change-Id: I46bb7e470e61c64ff54ac5aec5554b828c1ca4be Reviewed-on: https://go-review.googlesource.com/c/go/+/587597 Reviewed-by: Carlos Amedee <carlos@golang.org> Auto-Submit: Michael Knyszek <mknyszek@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> |
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README.md
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