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From: Miaohe Lin <linmiaohe@huawei.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: <akpm@linux-foundation.org>, <shy828301@gmail.com>,
	<willy@infradead.org>, <zokeefe@google.com>, <linux-mm@kvack.org>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 02/16] mm/huge_memory: access vm_page_prot with READ_ONCE in remove_migration_pmd
Date: Thu, 23 Jun 2022 20:03:41 +0800	[thread overview]
Message-ID: <7ee4a597-d7cb-f387-5613-f51b17262745@huawei.com> (raw)
In-Reply-To: <20220623031401.wdyt5ylin4aijzhh@box.shutemov.name>

On 2022/6/23 11:14, Kirill A. Shutemov wrote:
> On Thu, Jun 23, 2022 at 01:06:13AM +0800, Miaohe Lin wrote:
>> vma->vm_page_prot is read lockless from the rmap_walk, it may be updated
>> concurrently. Using READ_ONCE to prevent the risk of reading intermediate
>> values.
> 
> Have you checked all other vm_page_prot reads that they hold mmap_lock?

I took a glance when I made this patch.

> 
> I think the right fix would be to provide a helper to read vm_page_prot
> which does READ_ONCE() and use it everywhere. This seems more sustainable.
> 

This patch is inspired from the below commit
  6d2329f8872f ("mm: vm_page_prot: update with WRITE_ONCE/READ_ONCE")

It changed all the places that need to use READ_ONCE. But remove_migration_pmd
is missed due to it's introduced later. It looks fine to add a helper to read
vm_page_prot which does READ_ONCE() but READ_ONCE is unneeded while under the
mmap_lock, so might it be a little overkill to add a helper because the helper
is used iff mmap_lock is not held?

Thanks.

  reply	other threads:[~2022-06-23 12:03 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-22 17:06 [PATCH 00/16] A few cleanup patches for huge_memory Miaohe Lin
2022-06-22 17:06 ` [PATCH 01/16] mm/huge_memory: use flush_pmd_tlb_range in move_huge_pmd Miaohe Lin
2022-06-23  6:30   ` Muchun Song
2022-06-24 18:32     ` Zach O'Keefe
2022-06-22 17:06 ` [PATCH 02/16] mm/huge_memory: access vm_page_prot with READ_ONCE in remove_migration_pmd Miaohe Lin
2022-06-23  3:14   ` Kirill A. Shutemov
2022-06-23 12:03     ` Miaohe Lin [this message]
2022-06-24 18:40       ` Zach O'Keefe
2022-06-25  3:17         ` Miaohe Lin
2022-06-22 17:06 ` [PATCH 03/16] mm/huge_memory: fix comment of __pud_trans_huge_lock Miaohe Lin
2022-06-23  6:32   ` Muchun Song
2022-06-24 18:47   ` Zach O'Keefe
2022-06-25  3:33     ` Miaohe Lin
2022-06-24 18:56   ` Matthew Wilcox
2022-06-25  3:32     ` Miaohe Lin
2022-06-22 17:06 ` [PATCH 04/16] mm/huge_memory: use helper touch_pud in huge_pud_set_accessed Miaohe Lin
2022-06-23  6:42   ` Muchun Song
2022-06-23 12:08     ` Miaohe Lin
2022-06-22 17:06 ` [PATCH 05/16] mm/huge_memory: use helper touch_pmd in huge_pmd_set_accessed Miaohe Lin
2022-06-23  6:43   ` Muchun Song
2022-06-22 17:06 ` [PATCH 06/16] mm/huge_memory: rename mmun_start to haddr in remove_migration_pmd Miaohe Lin
2022-06-23  6:46   ` Muchun Song
2022-06-22 17:06 ` [PATCH 07/16] mm/huge_memory: minor cleanup for split_huge_pages_pid Miaohe Lin
2022-06-23  3:22   ` Kirill A. Shutemov
2022-06-23 12:07     ` Miaohe Lin
2022-06-22 17:06 ` [PATCH 08/16] mm/huge_memory: use helper macro __ATTR_RW Miaohe Lin
2022-06-23  6:49   ` Muchun Song
2022-06-22 17:06 ` [PATCH 09/16] mm/huge_memory: fix comment in zap_huge_pud Miaohe Lin
2022-06-22 17:06 ` [PATCH 10/16] mm/huge_memory: check pmd_present first in is_huge_zero_pmd Miaohe Lin
2022-06-23  6:59   ` Muchun Song
2022-06-22 17:06 ` [PATCH 11/16] mm/huge_memory: try to free subpage in swapcache when possible Miaohe Lin
2022-06-22 17:06 ` [PATCH 12/16] mm/huge_memory: minor cleanup for split_huge_pages_all Miaohe Lin
2022-06-22 17:06 ` [PATCH 13/16] mm/huge_memory: add helper __get_deferred_split_queue Miaohe Lin
2022-06-23  7:03   ` Muchun Song
2022-06-23 12:11     ` Miaohe Lin
2022-06-22 17:06 ` [PATCH 14/16] mm/huge_memory: fix comment of page_deferred_list Miaohe Lin
2022-06-23  7:24   ` Muchun Song
2022-06-23 12:26     ` Miaohe Lin
2022-06-24 17:09       ` Zach O'Keefe
2022-06-25  3:18         ` Miaohe Lin
2022-06-22 17:06 ` [PATCH 15/16] mm/huge_memory: correct comment of prep_transhuge_page Miaohe Lin
2022-06-23  7:26   ` Muchun Song
2022-06-22 17:06 ` [PATCH 16/16] mm/huge_memory: comment the subtle logic in __split_huge_pmd Miaohe Lin

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