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Date:   Mon, 30 May 2022 16:02:23 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Miaohe Lin <linmiaohe@huawei.com>
Cc:     <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/3] mm/swapfile: make security_vm_enough_memory_mm()
 work as expected
Message-Id: <20220530160223.63ae3bdef7420f252d7366ed@linux-foundation.org>
In-Reply-To: <20220527092626.31883-2-linmiaohe@huawei.com>
References: <20220527092626.31883-1-linmiaohe@huawei.com>
        <20220527092626.31883-2-linmiaohe@huawei.com>
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On Fri, 27 May 2022 17:26:24 +0800 Miaohe Lin <linmiaohe@huawei.com> wrote:

> security_vm_enough_memory_mm() checks whether a process has enough memory
> to allocate a new virtual mapping. And total_swap_pages is considered as
> available memory while swapoff tries to make sure there's enough memory
> that can hold the swapped out memory. But total_swap_pages contains the
> swap space that is being swapoff. So security_vm_enough_memory_mm() will
> success even if there's no memory to hold the swapped out memory because
> total_swap_pages always greater than or equal to p->pages.
> 
> In order to fix it, p->pages should be retracted from total_swap_pages
> first and then check whether there's enough memory for inuse swap pages.

User-visible impact?

If I'm understanding correctly, there's a risk that this fix will cause
existing setups to newly fail when attempting swapoff()?