[release-branch.go1.23] internal/weak: shade pointer in weak-to-strong conversion
There's a bug in the weak-to-strong conversion in that creating the
*only* strong pointer to some weakly-held object during the mark phase
may result in that object not being properly marked.
The exact mechanism for this is that the new strong pointer will always
point to a white object (because it was only weakly referenced up until
this point) and it can then be stored in a blackened stack, hiding it
from the garbage collector.
This "hide a white pointer in the stack" problem is pretty much exactly
what the Yuasa part of the hybrid write barrier is trying to catch, so
we need to do the same thing the write barrier would do: shade the
pointer.
Added a test and confirmed that it fails with high probability if the
pointer shading is missing.
For #69210.
Fixes #69240.
Change-Id: Iaae64ae95ea7e975c2f2c3d4d1960e74e1bd1c3f
Reviewed-on: https://go-review.googlesource.com/c/go/+/610396
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
(cherry picked from commit
79fd633632cdbaf9ca38f7559e5abb5c07fbbd9d)
Reviewed-on: https://go-review.googlesource.com/c/go/+/610696
Auto-Submit: Dmitri Shuralyov <dmitshur@google.com>