623e2c4603
We lazily map the bitmap and spans areas as the heap grows. However, right now we're very slightly too lazy. Specifically, the following can happen on 32-bit: 1. mallocinit fails to allocate any heap arena, so arena_used == arena_alloc == arena_end == bitmap. 2. There's less than 256MB between the end of the bitmap mapping and the next mapping. 3. On the first allocation, mheap.sysAlloc sees that there's not enough room in [arena_alloc, arena_end) because there's no room at all. It gets a 256MB mapping from somewhere *lower* in the address space than arena_used and sets arena_alloc and arena_end to this hole. 4. Since the new arena_alloc is lower than arena_used, mheap.sysAlloc doesn't bother to call mheap.setArenaUsed, so we still don't have a bitmap mapping or a spans array mapping. 5. mheap.grow, which called mheap.sysAlloc, attempts to fill in the spans array and crashes. Fix this by mapping the metadata regions for the initial arena_used when the heap is initialized, rather than trying to wait for an allocation. This maintains the intended invariant that the structures are always mapped for [arena_start, arena_used). Fixes #21044. Change-Id: I4422375a6e234b9f979d22135fc63ae3395946b0 Reviewed-on: https://go-review.googlesource.com/51714 Run-TryBot: Austin Clements <austin@google.com> Reviewed-by: Ian Lance Taylor <iant@golang.org> |
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