a25a77aed2
The runtime currently has two different notions of sweep completion: 1. All spans are either swept or have begun sweeping. 2. The sweeper has *finished* sweeping all spans. Most things depend on condition 1. Notably, GC correctness depends on condition 1, but since all sweep operations a non-preemptible, the STW at the beginning of GC forces condition 1 to become condition 2. runtime.GC(), however, depends on condition 2, since the intent is to complete a complete GC cycle, and also update the heap profile (which can only be done after sweeping is complete). However, the way we compute condition 2 is racy right now and may in fact only indicate condition 1. Specifically, sweepone blocks condition 2 until all sweepone calls are done, but there are many other ways to enter the sweeper that don't block this. Hence, sweepone may see that there are no more spans in the sweep list and see that it's the last sweepone and declare sweeping done, while there's some other sweeper still working on a span. Fix this by making sure every entry to the sweeper participates in the protocol that blocks condition 2. To make sure we get this right, this CL introduces a type to track sweep blocking and (lightly) enforces span sweep ownership via the type system. This has the nice side-effect of abstracting the pattern of acquiring sweep ownership that's currently repeated in many different places. Fixes #45315. Change-Id: I7fab30170c5ae14c8b2f10998628735b8be6d901 Reviewed-on: https://go-review.googlesource.com/c/go/+/307915 Trust: Austin Clements <austin@google.com> Run-TryBot: Austin Clements <austin@google.com> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Michael Knyszek <mknyszek@google.com> |
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