febe7b8e2a
When the GC is scanning some memory (possibly conservatively), finding a pointer, while concurrently another goroutine is allocating an object at the same address as the found pointer, the GC may see the pointer before the object and/or the heap bits are initialized. This may cause the GC to see bad pointers and possibly crash. To prevent this, we make it that the scanner can only see the object as allocated after the object and the heap bits are initialized. Currently the allocator uses freeindex to find the next available slot, and that code is coupled with updating the free index to a new slot past it. The scanner also uses the freeindex to determine if an object is allocated. This is somewhat racy. This CL makes the scanner use a different field, which is only updated after the object initialization (and a memory barrier). Fixes #54596. Change-Id: I2a57a226369926e7192c253dd0d21d3faf22297c Reviewed-on: https://go-review.googlesource.com/c/go/+/449017 Reviewed-by: Austin Clements <austin@google.com> Reviewed-by: Michael Knyszek <mknyszek@google.com> Run-TryBot: Cherry Mui <cherryyz@google.com> TryBot-Result: Gopher Robot <gobot@golang.org> |
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