[PATCH v3 1/2] Revert "kasan: drop skip_kasan_poison variable in free_pages_prepare"

[Andrew Morton]

On Tue, 28 Feb 2023 16:35:44 -0800 Peter Collingbourne <pcc at google.com> wrote:

> This reverts commit 487a32ec24be819e747af8c2ab0d5c515508086a.
> 
> The should_skip_kasan_poison() function reads the PG_skip_kasan_poison
> flag from page->flags. However, this line of code in free_pages_prepare():
> 
> page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
> 
> clears most of page->flags, including PG_skip_kasan_poison, before calling
> should_skip_kasan_poison(), which meant that it would never return true
> as a result of the page flag being set. Therefore, fix the code to call
> should_skip_kasan_poison() before clearing the flags, as we were doing
> before the reverted patch.

What are the user visible effects of this change?

> Cc: <stable at vger.kernel.org> # 6.1

Especially if it's cc:stable.

Thanks.