3675bff55d
heapBits.bits is used during bulkBarrierPreWrite via heapBits.isPointer, which means it must not be preempted. If it is preempted, several bad things can happen: 1. This could allow a GC phase change, and the resulting shear between the barriers and the memory writes could result in a lost pointer. 2. Since bulkBarrierPreWrite uses the P's local write barrier buffer, if it also migrates to a different P, it could try to append to the write barrier buffer concurrently with another write barrier. This can result in the buffer's next pointer skipping over its end pointer, which results in a buffer overflow that can corrupt arbitrary other fields in the Ps (or anything in the heap, really, but it'll probably crash from the corrupted P quickly). Fix this by marking heapBits.bits go:nosplit. This would be the perfect use for a recursive no-preempt annotation (#21314). This doesn't actually affect any binaries because this function was always inlined anyway. (I discovered it when I was modifying heapBits and make h.bits() no longer inline, which led to rampant crashes from problem 2 above.) Updates #22987 and #22988 (but doesn't fix because it doesn't actually change the generated code). Change-Id: I60ebb928b1233b0613361ac3d0558d7b1cb65610 Reviewed-on: https://go-review.googlesource.com/83015 Run-TryBot: Austin Clements <austin@google.com> Reviewed-by: Matthew Dempsky <mdempsky@google.com> Reviewed-by: Rick Hudson <rlh@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> |
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The Go Programming Language
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