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Shutemov" To: Miaohe Lin 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 Message-ID: <20220623031401.wdyt5ylin4aijzhh@box.shutemov.name> References: <20220622170627.19786-1-linmiaohe@huawei.com> <20220622170627.19786-3-linmiaohe@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220622170627.19786-3-linmiaohe@huawei.com> ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=pass header.d=shutemov-name.20210112.gappssmtp.com header.s=20210112 header.b="n3/SAojr"; dmarc=none; spf=none (imf23.hostedemail.com: domain of kirill@shutemov.name has no SPF policy when checking 209.85.208.170) smtp.mailfrom=kirill@shutemov.name ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655953912; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=5jDNpLxr7cGIqADzC3sdvFFhgsnexUiy02PrUDQv/Rc=; b=gWxmpBi5vi7HaBZsPKAA+DSbqBhKTDjjHAf0U8psOWdl96uRU6xe+tuixUwD+X4x1/42Fc tj4cpvD4Kb95sGn7JPHw9nnX5hKE4/IkQ94JGim7VaaBJ1QeJxwWDaI7vxbWrxIOGTkW9Q ldANIHDI9QBufQToXt1FQo4cDZSCs8U= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655953912; a=rsa-sha256; cv=none; b=i9b/9pPlwiYs99k8H45Pyk3+tpjEHyRIAbC2jRhJzN0b8IXVo/ETxaI/5oBB5nVQhgbXXb dbMOYL/tfCKeGBN026O2LwKZUM3uOTMgqyLqrE2Yv5pSxHr9h+tV2uTS9d5l2PPWsJlQ0a LPqGZIEh70HDkBu1ZX17osPNQZTSWY8= X-Rspam-User: Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=shutemov-name.20210112.gappssmtp.com header.s=20210112 header.b="n3/SAojr"; dmarc=none; spf=none (imf23.hostedemail.com: domain of kirill@shutemov.name has no SPF policy when checking 209.85.208.170) smtp.mailfrom=kirill@shutemov.name X-Stat-Signature: dyhof5wo38638tfxzaxdm65o5k7ggz7d X-Rspamd-Queue-Id: 0446414001B X-Rspamd-Server: rspam12 X-HE-Tag: 1655953911-534767 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 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. -- Kirill A. Shutemov