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Date:   Fri, 6 Oct 2023 10:57:19 -0700
From:   Mike Kravetz <mike.kravetz@oracle.com>
To:     riel@surriel.com
Cc:     linux-kernel@vger.kernel.org, kernel-team@meta.com,
        linux-mm@kvack.org, akpm@linux-foundation.org,
        muchun.song@linux.dev, leit@meta.com, willy@infradead.org,
        stable@kernel.org
Subject: Re: [PATCH 3/4] hugetlbfs: close race between MADV_DONTNEED and page
 fault
Message-ID: <20231006175719.GA3861@monkey>
References: <20231006040020.3677377-1-riel@surriel.com>
 <20231006040020.3677377-4-riel@surriel.com>
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On 10/05/23 23:59, riel@surriel.com wrote:
> From: Rik van Riel <riel@surriel.com>
> 
> Malloc libraries, like jemalloc and tcalloc, take decisions on when
> to call madvise independently from the code in the main application.
> 
> This sometimes results in the application page faulting on an address,
> right after the malloc library has shot down the backing memory with
> MADV_DONTNEED.
> 
> Usually this is harmless, because we always have some 4kB pages
> sitting around to satisfy a page fault. However, with hugetlbfs
> systems often allocate only the exact number of huge pages that
> the application wants.
> 
> Due to TLB batching, hugetlbfs MADV_DONTNEED will free pages outside of
> any lock taken on the page fault path, which can open up the following
> race condition:
> 
>        CPU 1                            CPU 2
> 
>        MADV_DONTNEED
>        unmap page
>        shoot down TLB entry
>                                        page fault
>                                        fail to allocate a huge page
>                                        killed with SIGBUS
>        free page
> 
> Fix that race by pulling the locking from __unmap_hugepage_final_range
> into helper functions called from zap_page_range_single. This ensures
> page faults stay locked out of the MADV_DONTNEED VMA until the
> huge pages have actually been freed.
> 
> Signed-off-by: Rik van Riel <riel@surriel.com>
> Cc: stable@kernel.org
> Fixes: 04ada095dcfc ("hugetlb: don't delete vma_lock in hugetlb MADV_DONTNEED processing")
> ---
>  include/linux/hugetlb.h | 35 +++++++++++++++++++++++++++++++++--
>  mm/hugetlb.c            | 34 ++++++++++++++++++++++------------
>  mm/memory.c             | 13 ++++++++-----
>  3 files changed, 63 insertions(+), 19 deletions(-)

Thanks for all the revisions,

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
-- 
Mike Kravetz