linux-kernel - Re: [PATCH 1/2] hugetlbfs: extend hugetlb_vma

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Message-ID: <42128925a9c36e7bc9d55ca422e36ff880999087.camel@surriel.com>
Date:   Thu, 21 Sep 2023 20:37:03 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...a.com,
        linux-mm@...ck.org, akpm@...ux-foundation.org,
        muchun.song@...ux.dev, leit@...a.com
Subject: Re: [PATCH 1/2] hugetlbfs: extend hugetlb_vma_lock to private VMAs

On Thu, 2023-09-21 at 15:42 -0700, Mike Kravetz wrote:
> On 09/19/23 22:16, riel@...riel.com wrote:
> > From: Rik van Riel <riel@...riel.com>
> > 
> > Extend the locking scheme used to protect shared hugetlb mappings
> > from truncate vs page fault races, in order to protect private
> > hugetlb mappings (with resv_map) against MADV_DONTNEED.
> > 
> > Add a read-write semaphore to the resv_map data structure, and
> > use that from the hugetlb_vma_(un)lock_* functions, in preparation
> > for closing the race between MADV_DONTNEED and page faults.
> > 
> > Signed-off-by: Rik van Riel <riel@...riel.com>
> > ---
> >  include/linux/hugetlb.h |  6 ++++++
> >  mm/hugetlb.c            | 36 ++++++++++++++++++++++++++++++++----
> >  2 files changed, 38 insertions(+), 4 deletions(-)
> 
> This looks straight forward.
> 
> However, I ran just this patch through libhugetlbfs test suite and it
> hung on
> misaligned_offset (2M: 32).
> https://github.com/libhugetlbfs/libhugetlbfs/blob/master/tests/misaligned_offset.c

Ah, so that's why I couldn't find hugetlbfs tests in the kernel
selftests directory. They're in libhugetlbfs.

I'll play around with those tests tomorrow. Let me see what's
going on.

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