tree ecac6792565547680e0a123403a88e3c5d59ca0d
parent bbee5236cd64a11a2bfd194eb9f809f51cae0870
author Michael Anthony Knyszek <mknyszek@google.com> 1599670338 +0000
committer Dmitri Shuralyov <dmitshur@golang.org> 1599763098 +0000

[release-branch.go1.15] runtime: fix ReadMemStatsSlow's and CheckScavengedBits' chunk iteration

Both ReadMemStatsSlow and CheckScavengedBits iterate over the page
allocator's chunks but don't actually check if they exist. During the
development process the chunks index became sparse, so now this was a
possibility. If the runtime tests' heap is sparse we might end up
segfaulting in either one of these functions, though this will generally
be very rare.

The pattern here to return nil for a nonexistent chunk is also useful
elsewhere, so this change introduces tryChunkOf which won't throw, but
might return nil. It also updates the documentation of chunkOf.

For #41296.
Fixes #41317.

Change-Id: Id5ae0ca3234480de1724fdf2e3677eeedcf76fa0
Reviewed-on: https://go-review.googlesource.com/c/go/+/253777
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
(cherry picked from commit 34835df04891a1d54394888b763af88f9476101d)
Reviewed-on: https://go-review.googlesource.com/c/go/+/253917