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

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Date:   Fri, 24 Sep 2021 10:14:21 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
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, Sep 23, 2021 at 07:19:41PM -0700, Andrew Morton wrote:
> 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?

Not sure how we normally handle such case for selftests, but I agree.

Btw, 8ba6e8640844 is merged in 5.14, so the only stable branch that will need
it will be 5.14.y; it can be applied cleanly there.

Thanks,

-- 
Peter Xu