From: Miaohe Lin <linmiaohe@huawei.com>
To: Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>
Subject: Re: [PATCH] ksm: Revert "use GET_KSM_PAGE_NOLOCK to get ksm page in remove_rmap_item_from_tree()"
Date: Mon, 10 May 2021 14:57:06 +0800 [thread overview]
Message-ID: <0e04877c-5b2d-b810-7464-108e793b84d3@huawei.com> (raw)
In-Reply-To: <alpine.LSU.2.11.2105092253500.1127@eggly.anvils>
On 2021/5/10 13:59, Hugh Dickins wrote:
> This reverts commit 3e96b6a2e9ad929a3230a22f4d64a74671a0720b.
> General Protection Fault in rmap_walk_ksm() under memory pressure:
> remove_rmap_item_from_tree() needs to take page lock, of course.
>
I'am really sorry about it! And many thanks for this bugfix!
It seems rmap_walk_ksm() relies on the page lock to protect against
concurrent modifications to that page's node of the stable tree.
Could you please add a comment in remove_rmap_item_from_tree() to
clarify this in case similar trouble again? Many thanks!
> Signed-off-by: Hugh Dickins <hughd@google.com>
> ---
>
> mm/ksm.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> --- 5.13-rc1/mm/ksm.c 2021-05-09 17:03:44.010422188 -0700
> +++ linux/mm/ksm.c 2021-05-09 22:12:39.403008350 -0700
> @@ -776,11 +776,12 @@ static void remove_rmap_item_from_tree(s
> struct page *page;
>
> stable_node = rmap_item->head;
> - page = get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK);
> + page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
> if (!page)
> goto out;
>
> hlist_del(&rmap_item->hlist);
> + unlock_page(page);
> put_page(page);
>
> if (!hlist_empty(&stable_node->hlist))
> .
>
next prev parent reply other threads:[~2021-05-10 6:57 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-10 5:59 [PATCH] ksm: Revert "use GET_KSM_PAGE_NOLOCK to get ksm page in remove_rmap_item_from_tree()" Hugh Dickins
2021-05-10 6:57 ` Miaohe Lin [this message]
2021-05-10 23:42 ` Hugh Dickins
2021-05-11 1:40 ` Miaohe Lin
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