From: "Huang, Ying" <ying.huang@intel.com>
To: Miaohe Lin <linmiaohe@huawei.com>
Cc: <akpm@linux-foundation.org>, <hannes@cmpxchg.org>,
<mhocko@suse.com>, <iamjoonsoo.kim@lge.com>, <vbabka@suse.cz>,
<alex.shi@linux.alibaba.com>, <willy@infradead.org>,
<minchan@kernel.org>, <richard.weiyang@gmail.com>,
<hughd@google.com>, <tim.c.chen@linux.intel.com>,
<linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>
Subject: Re: [PATCH 4/5] mm/swap_state: fix potential faulted in race in swap_ra_info()
Date: Mon, 12 Apr 2021 08:55:01 +0800 [thread overview]
Message-ID: <87v98swcd6.fsf@yhuang6-desk1.ccr.corp.intel.com> (raw)
In-Reply-To: <d88fbae4-20f5-0c7f-1c9b-b814b87ab222@huawei.com> (Miaohe Lin's message of "Fri, 9 Apr 2021 17:00:02 +0800")
Miaohe Lin <linmiaohe@huawei.com> writes:
> On 2021/4/9 16:50, Huang, Ying wrote:
>> Miaohe Lin <linmiaohe@huawei.com> writes:
>>
>>> While we released the pte lock, somebody else might faulted in this pte.
>>> So we should check whether it's swap pte first to guard against such race
>>> or swp_type would be unexpected. And we can also avoid some unnecessary
>>> readahead cpu cycles possibly.
>>>
>>> Fixes: ec560175c0b6 ("mm, swap: VMA based swap readahead")
>>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>>> ---
>>> mm/swap_state.c | 13 +++++++++----
>>> 1 file changed, 9 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/mm/swap_state.c b/mm/swap_state.c
>>> index 709c260d644a..3bf0d0c297bc 100644
>>> --- a/mm/swap_state.c
>>> +++ b/mm/swap_state.c
>>> @@ -724,10 +724,10 @@ static void swap_ra_info(struct vm_fault *vmf,
>>> {
>>> struct vm_area_struct *vma = vmf->vma;
>>> unsigned long ra_val;
>>> - swp_entry_t entry;
>>> + swp_entry_t swap_entry;
>>> unsigned long faddr, pfn, fpfn;
>>> unsigned long start, end;
>>> - pte_t *pte, *orig_pte;
>>> + pte_t *pte, *orig_pte, entry;
>>> unsigned int max_win, hits, prev_win, win, left;
>>> #ifndef CONFIG_64BIT
>>> pte_t *tpte;
>>> @@ -742,8 +742,13 @@ static void swap_ra_info(struct vm_fault *vmf,
>>>
>>> faddr = vmf->address;
>>> orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
>>> - entry = pte_to_swp_entry(*pte);
>>> - if ((unlikely(non_swap_entry(entry)))) {
>>> + entry = *pte;
>>> + if (unlikely(!is_swap_pte(entry))) {
>>> + pte_unmap(orig_pte);
>>> + return;
>>> + }
>>> + swap_entry = pte_to_swp_entry(entry);
>>> + if ((unlikely(non_swap_entry(swap_entry)))) {
>>> pte_unmap(orig_pte);
>>> return;
>>> }
>>
>> This isn't a real issue. entry or swap_entry isn't used in this
>
> Agree. It seems the entry or swap_entry here is just used for check whether
> pte is still valid swap_entry.
If you check the git history, you will find that the check has been
necessary before. Because the function is used earlier in
do_swap_page() at that time.
Best Regards,
Huang, Ying
next prev parent reply other threads:[~2021-04-12 0:55 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-08 13:08 [PATCH 0/5] close various race windows for swap Miaohe Lin
2021-04-08 13:08 ` [PATCH 3/5] mm/swap_state: fix get_shadow_from_swap_cache() race with swapoff Miaohe Lin
2021-04-13 1:33 ` Huang, Ying
2021-04-14 2:42 ` Miaohe Lin
2021-04-08 13:08 ` [PATCH 4/5] mm/swap_state: fix potential faulted in race in swap_ra_info() Miaohe Lin
2021-04-09 8:50 ` Huang, Ying
2021-04-09 9:00 ` Miaohe Lin
2021-04-12 0:55 ` Huang, Ying [this message]
2021-04-12 3:17 ` Miaohe Lin
2021-04-08 13:08 ` [PATCH 5/5] mm/swap_state: fix swap_cluster_readahead() race with swapoff Miaohe Lin
2021-04-13 1:36 ` Huang, Ying
2021-04-14 2:43 ` Miaohe Lin
2021-04-08 14:55 ` [PATCH 0/5] close various race windows for swap riteshh
2021-04-09 8:01 ` Miaohe Lin
[not found] ` <20210408130820.48233-2-linmiaohe@huawei.com>
2021-04-12 3:30 ` [PATCH 1/5] mm/swapfile: add percpu_ref support " Huang, Ying
2021-04-12 6:59 ` Miaohe Lin
2021-04-12 7:24 ` Huang, Ying
2021-04-13 12:39 ` Miaohe Lin
2021-04-14 1:17 ` Huang, Ying
2021-04-14 1:58 ` Miaohe Lin
2021-04-14 2:06 ` Huang, Ying
2021-04-14 3:44 ` Dennis Zhou
2021-04-14 3:59 ` Huang, Ying
2021-04-14 4:05 ` Dennis Zhou
2021-04-14 5:44 ` Huang, Ying
2021-04-14 14:53 ` Dennis Zhou
2021-04-15 3:16 ` Miaohe Lin
2021-04-15 4:20 ` Dennis Zhou
2021-04-15 9:17 ` Miaohe Lin
2021-04-15 5:24 ` Huang, Ying
2021-04-15 14:31 ` Dennis Zhou
2021-04-16 0:54 ` Huang, Ying
2021-04-16 2:27 ` Miaohe Lin
2021-04-16 6:25 ` Huang, Ying
2021-04-16 8:30 ` Miaohe Lin
[not found] ` <20210408130820.48233-3-linmiaohe@huawei.com>
2021-04-08 21:34 ` [PATCH 2/5] swap: fix do_swap_page() race with swapoff Tim Chen
2021-04-09 8:42 ` Miaohe Lin
2021-04-09 17:17 ` Tim Chen
2021-04-10 3:17 ` Miaohe Lin
2021-04-12 1:44 ` Huang, Ying
2021-04-12 3:24 ` Miaohe Lin
2021-04-13 1:27 ` Huang, Ying
2021-04-13 19:24 ` Tim Chen
2021-04-14 1:04 ` Huang, Ying
2021-04-14 2:20 ` Miaohe Lin
2021-04-14 16:13 ` Tim Chen
2021-04-15 3:19 ` Miaohe Lin
2021-04-14 2:55 ` Miaohe Lin
2021-04-14 3:07 ` Huang, Ying
2021-04-14 3:27 ` Miaohe Lin
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