From: Yu Zhao <yuzhao@google.com>
To: Mauricio Faria de Oliveira <mfo@canonical.com>
Cc: Minchan Kim <minchan@kernel.org>,
"Huang, Ying" <ying.huang@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Yang Shi <shy828301@gmail.com>, Miaohe Lin <linmiaohe@huawei.com>,
linux-mm@kvack.org, linux-block@vger.kernel.org
Subject: Re: [PATCH v3] mm: fix race between MADV_FREE reclaim and blkdev direct IO read
Date: Wed, 2 Feb 2022 12:56:36 -0700 [thread overview]
Message-ID: <Yfrh9F67ligMDUB7@google.com> (raw)
In-Reply-To: <20220131230255.789059-1-mfo@canonical.com>
On Mon, Jan 31, 2022 at 08:02:55PM -0300, Mauricio Faria de Oliveira wrote:
> Problem:
> =======
Thanks for the update. A couple of quick questions:
> Userspace might read the zero-page instead of actual data from a
> direct IO read on a block device if the buffers have been called
> madvise(MADV_FREE) on earlier (this is discussed below) due to a
> race between page reclaim on MADV_FREE and blkdev direct IO read.
1) would page migration be affected as well?
> @@ -1599,7 +1599,30 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>
> /* MADV_FREE page check */
> if (!PageSwapBacked(page)) {
> - if (!PageDirty(page)) {
> + int ref_count, map_count;
> +
> + /*
> + * Synchronize with gup_pte_range():
> + * - clear PTE; barrier; read refcount
> + * - inc refcount; barrier; read PTE
> + */
> + smp_mb();
> +
> + ref_count = page_count(page);
> + map_count = page_mapcount(page);
> +
> + /*
> + * Order reads for page refcount and dirty flag;
> + * see __remove_mapping().
> + */
> + smp_rmb();
2) why does it need to order against __remove_mapping()? It seems to
me that here (called from the reclaim path) it can't race with
__remove_mapping() because both lock the page.
> + /*
> + * The only page refs must be from the isolation
> + * plus one or more rmap's (dropped by discard:).
> + */
> + if ((ref_count == 1 + map_count) &&
> + !PageDirty(page)) {
> /* Invalidate as we cleared the pte */
> mmu_notifier_invalidate_range(mm,
> address, address + PAGE_SIZE);
next prev parent reply other threads:[~2022-02-02 19:56 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-31 23:02 [PATCH v3] mm: fix race between MADV_FREE reclaim and blkdev direct IO read Mauricio Faria de Oliveira
2022-01-31 23:43 ` Andrew Morton
2022-02-01 2:23 ` Mauricio Faria de Oliveira
2022-02-02 14:03 ` Christoph Hellwig
2022-02-02 16:29 ` Mauricio Faria de Oliveira
2022-02-02 19:56 ` Yu Zhao [this message]
2022-02-02 21:27 ` Mauricio Faria de Oliveira
2022-02-02 21:53 ` Yu Zhao
2022-02-03 22:17 ` Mauricio Faria de Oliveira
2022-02-04 5:56 ` Yu Zhao
2022-02-04 7:03 ` John Hubbard
2022-02-04 18:59 ` Mauricio Faria de Oliveira
2022-02-04 18:58 ` Mauricio Faria de Oliveira
2022-02-16 6:48 ` Huang, Ying
2022-02-16 21:58 ` Yu Zhao
2022-02-16 22:00 ` Yu Zhao
2022-02-17 6:08 ` Huang, Ying
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