linux-kernel - Re: [PATCH] mm/userfaultfd: selftests: Fix memory corruption with thp enabled

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Date:   Thu, 23 Sep 2021 19:19:41 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Nadav Amit <nadav.amit@...il.com>, Li Wang <liwan@...hat.com>
Subject: Re: [PATCH] mm/userfaultfd: selftests: Fix memory corruption with
 thp enabled

On Thu, 23 Sep 2021 19:25:12 -0400 Peter Xu <peterx@...hat.com> wrote:

> In RHEL's gating selftests we've encountered memory corruption in the uffd
> event test even with upstream kernel:
> 
> ...
>
> 
> We can mark the Fixes tag upon 0db282ba2c12 as it's reported to only happen
> there, however the real "Fixes" IMHO should be 8ba6e8640844, as before that
> commit we'll always do explicit release_pages() before registration of uffd,
> and 8ba6e8640844 changed that logic by adding extra unmap/map and we didn't
> release the pages at the right place.  Meanwhile I don't have a solid glue
> anyway on whether posix_memalign() could always avoid triggering this bug,
> hence it's safer to attach this fix to commit 8ba6e8640844.
> 

Thanks.  I added a cc:stable to this.  I don't think we want selftests
in older kernels to be falsely reporting kernel bugs?