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Mon, 01 Aug 2022 21:07:04 -0700 (PDT) Date: Tue, 2 Aug 2022 12:07:00 +0800 From: Muchun Song To: Miaohe Lin Cc: Linux-MM , linux-kernel , Andrew Morton , Mike Kravetz , Naoya Horiguchi Subject: Re: [bug report] mm, hwpoison: memory_failure races with alloc_fresh_huge_page/free_huge_page Message-ID: References: <3c542543-0965-ef60-4627-1a4116077a5b@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3c542543-0965-ef60-4627-1a4116077a5b@huawei.com> ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=pass header.d=bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b=S9eDn9MA; spf=pass (imf11.hostedemail.com: domain of songmuchun@bytedance.com designates 209.85.214.182 as permitted sender) smtp.mailfrom=songmuchun@bytedance.com; dmarc=pass (policy=none) header.from=bytedance.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1659413227; a=rsa-sha256; cv=none; b=sV0XPvxSym4IB1pHaIFF/AD0Ty6WSXLq9MrNNvs19CiLDcXIeRSon1BHxmQB4bkLGErczL LHDjsHfXmskgND/dbOU6HcjIDOBiiAW2uDN0l63L750gFOp084+E2uVTC8/JC5qU2WqPri qLQ+DL6IXrUd+bmAOQnZJa1jseFzcKI= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1659413227; 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=emO/aP9ZnO5urqHffk6lerV5ez7+dpluevKxfTa0sAA=; b=OQfLLj72e/5vtB65Cuv7Ck78VwTgwHOQGkivT0xQK/Hujuv2Et/eRreREqjWiqKpgii8D8 vSM08+lBrlMLxxG1qQgaEmr57FOkr8pILS196v8JgqJMN+HGH9lfZ72S9BT3SMOiQhbsWv pBQa3EiAyt2V3jCD/Enhr2VZX2nNtWE= X-Rspamd-Queue-Id: 92DA540052 Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b=S9eDn9MA; spf=pass (imf11.hostedemail.com: domain of songmuchun@bytedance.com designates 209.85.214.182 as permitted sender) smtp.mailfrom=songmuchun@bytedance.com; dmarc=pass (policy=none) header.from=bytedance.com X-Rspamd-Server: rspam01 X-Rspam-User: X-Stat-Signature: tjat778bnabkyeqyyrk9nex95ap7wbfd X-HE-Tag: 1659413226-327888 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Aug 02, 2022 at 10:00:50AM +0800, Miaohe Lin wrote: > Hi all: > When I investigate the mm/memory-failure.c code again, I found there's a possible race window > between memory_failure and alloc_fresh_huge_page/free_huge_page. Thank about the below scene: > > CPU 1 CPU 2 > alloc_fresh_huge_page -- page refcnt > 0 memory_failure > prep_new_huge_page get_huge_page_for_hwpoison > !PageHeadHuge -- so 2(not a hugepage) is returned > hugetlb_vmemmap_optimize -- subpages is read-only > set_compound_page_dtor -- PageHuge is true now, but too late!!! > TestSetPageHWPoison(p) > -- We might write to read-only subpages here!!! > > Another similar scene: > > CPU 1 CPU 2 > free_huge_page -- page refcnt == 0 and not PageHuge memory_failure > get_huge_page_for_hwpoison > !PageHeadHuge -- so 2(not a hugepage) is returned > TestSetPageHWPoison(p) > -- We might write to read-only subpages here!!! > hugetlb_vmemmap_restore -- subpages can be written to now, but too late!!! > I agree this race is possible, I have proposed this race in thread [1]. But I didn't think more how to solve it. [1] https://lore.kernel.org/linux-mm/20220623235153.2623702-1-naoya.horiguchi@linux.dev/T/#ma094a7cea7df8fd9a77a91551bf39077d89e23bd > I think the above scenes are possible. But I can't found a stable solution to fix it. Any suggestions? > Or is it not worth to fix it as it's too rare? Or am I miss something? > Luckily, the system will panic at once, which encountering this race. However, we don't see any bug report. If we have an easy way to fix it, I think it is worth. Just a quick reply, no suggestion/solutions from me. Thanks. > Any response would be appreciated! > > Thanks! >