runtime: pageAlloc.allocToCache updates pageAlloc.searchAddr in an invalid way

[mknyszek]

Currently the page allocator's allocToCache method can update the search address in such a way that it doesn't point into memory contained in pageAlloc.inUse, which violates a documented property.

The result of this is an occasional crash. A similar bug was fixed prior to the Go 1.14 release with https://golang.org/cl/216697, but that failed to take into account allocToCache. This is causing real failures and we should fix it ASAP. We should also backport it as there is no workaround available when you do run into it.

[gopherbot]

Change https://golang.org/cl/229577 mentions this issue: runtime: ensure allocToCache updates searchAddr in a valid way

[mknyszek]

@gopherbot Please open a backport issue for 1.14.

[gopherbot]

Backport issue(s) opened: #38606 (for 1.14).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://golang.org/wiki/MinorReleases.

[mknyszek]

CC @aclements @prattmic

[gopherbot]

Change https://golang.org/cl/230377 mentions this issue: [release-branch.go1.14] runtime: ensure allocToCache updates searchAddr in a valid way

[networkimprov]

This and the CL mentioned in the issue aren't a factor in 1.13?

[mknyszek]

@networkimprov That's correct.