From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id A5AC6C74A5B for ; Fri, 24 Mar 2023 01:56:50 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0216F6B0075; Thu, 23 Mar 2023 21:56:50 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id F13C56B0078; Thu, 23 Mar 2023 21:56:49 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E02CB6B007B; Thu, 23 Mar 2023 21:56:49 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id CDCC96B0075 for ; Thu, 23 Mar 2023 21:56:49 -0400 (EDT) Received: from smtpin09.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 91EE716082B for ; Fri, 24 Mar 2023 01:56:49 +0000 (UTC) X-FDA: 80602128138.09.52868E4 Received: from mail-yb1-f171.google.com (mail-yb1-f171.google.com [209.85.219.171]) by imf26.hostedemail.com (Postfix) with ESMTP id C3965140005 for ; Fri, 24 Mar 2023 01:56:47 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b="i/OsODyR"; spf=pass (imf26.hostedemail.com: domain of hughd@google.com designates 209.85.219.171 as permitted sender) smtp.mailfrom=hughd@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1679623007; 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=OsiMTy6N1RgTGOvTb4Xekz2TfgGYj4qNFGKLfiNrC5c=; b=sdoztpBpBvIAdq/CUw83kEuq5VemSs3x/JtT5lLdmHVpVXyfNDknCA3fuC95xeDv4nciNs dBQBar4G4gUyPhcuRd3y3mtBpjrHzqNndYamCLDb5Pr83h9G1A3HbxoSkN9Uc3l5yEiMVq 8xlUZjMh2iE274nBTid4ExjtauWVfxY= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b="i/OsODyR"; spf=pass (imf26.hostedemail.com: domain of hughd@google.com designates 209.85.219.171 as permitted sender) smtp.mailfrom=hughd@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1679623007; a=rsa-sha256; cv=none; b=cVCvPovxGtahi0BtKF6HaP0vmMLW418m4TZPHOUb4PpirrNpYONocoKITJPLUSuEluSlhg jxpi6VcKA5FfRZeECG/IMrOMEHMCuiwfpyiarZo0QPtxPe86Hbe+BjOXmDg7HjoJPjakdk AV56Y0KaYti0LG5rjZlYhYI5lG4slfs= Received: by mail-yb1-f171.google.com with SMTP id z83so581285ybb.2 for ; Thu, 23 Mar 2023 18:56:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; t=1679623007; h=mime-version:references:message-id:in-reply-to:subject:cc:to:from :date:from:to:cc:subject:date:message-id:reply-to; bh=OsiMTy6N1RgTGOvTb4Xekz2TfgGYj4qNFGKLfiNrC5c=; b=i/OsODyRFwhKGCQVE5cOGTdtvHCCj1uWMzF2K26hcBSijC8Bs40+uJrOhLxFbYU5z6 6UAmtrLHZO3hGGsrgY0Qi6Wr24Solw5pnxAXpRqqejv1QKhj15Hnoe0y66GD5GogEMMJ uy/BlrCfRTtxAyb0tiLsLk8DeyDYABIs2p5N7H+u4ZnG5fOeBodeZYRDuFNa1XmGSSgF VVU+G15TSxO7Bj1pvQDJv+mWp7bhdosjZhCKqIThklR+vB6hKeCl17Jv47VDXzhfEL6e fkD4a/RjHjBwdn/9jK2eWZqlAwM7pVq8cLCzYln2IEk5vlmcC572oIqH5nT6eEGJ7Wjt q2Uw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1679623007; h=mime-version:references:message-id:in-reply-to:subject:cc:to:from :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=OsiMTy6N1RgTGOvTb4Xekz2TfgGYj4qNFGKLfiNrC5c=; b=RHjLpp4NA+RY5aY8/gfSKwyfXK+EJJmER6MN5eDTXx0Efplj3jQ1MZtuSVLjYfk6Oy HSW4FGqaLfCn1i9OzQxJ0JfDGipc7alOm506iL3XBdGvluLMkEM60ft2fmQ0emYaFvzw uasE+4bSEE6FXvtFBPteIxwRIizlRah+zJACiBVPn4WzBCrZUCxeQ/OD1EL4Px/E7Yhf 99xpznaij0P5TKFoY95jpolTbKThU1MKFO4sbC7A8pxybTuFWiKh3dDsBuKGH5gDBoJ/ tMgkMbvQlnr0dEJcYQS07xmb2rDO352mys/RdW4caAoqVqAqqeQQR1Z7yCU2wv/yRb9o AD9g== X-Gm-Message-State: AAQBX9cVjmetMZqDT8HxA54Q0/CKjupMSgCZrOdbgCdOJ61cirexvsoh Qu8LrZ6iLB23K2OT9M/+ew5PBg== X-Google-Smtp-Source: AKy350YpjYImsNOySKYjBd7nGIWFGk6giMK3LiQUNQ9zymyu1GFBcYRTvVx6oVVhLqLV/H1dUZLH/g== X-Received: by 2002:a25:ad86:0:b0:b26:91a2:61bc with SMTP id z6-20020a25ad86000000b00b2691a261bcmr734070ybi.37.1679623006756; Thu, 23 Mar 2023 18:56:46 -0700 (PDT) Received: from ripple.attlocal.net (172-10-233-147.lightspeed.sntcca.sbcglobal.net. [172.10.233.147]) by smtp.gmail.com with ESMTPSA id j83-20020a252356000000b00b7767ca7469sm178947ybj.6.2023.03.23.18.56.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Mar 2023 18:56:45 -0700 (PDT) Date: Thu, 23 Mar 2023 18:56:34 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Song Liu cc: Matthew Wilcox , Hugh Dickins , Song Liu , Jiri Olsa , David Stevens , linux-mm@kvack.org, Andrew Morton , Peter Xu , "Kirill A . Shutemov" , Yang Shi , David Hildenbrand , Jiaqi Yan , linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 3/3] mm/khugepaged: maintain page cache uptodate flag In-Reply-To: Message-ID: References: <20230307052036.1520708-1-stevensd@google.com> <20230307052036.1520708-4-stevensd@google.com> <866d1a75-d462-563-dfd7-1aa2971a285b@google.com> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="-1463760895-38525656-1679623005=:6497" X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: C3965140005 X-Stat-Signature: r4yig3x6hwwzbabj3btxfuhbng1seou6 X-HE-Tag: 1679623007-820909 X-HE-Meta: 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 gw+YlwFr 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 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: This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. ---1463760895-38525656-1679623005=:6497 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE On Thu, 23 Mar 2023, Song Liu wrote: > On Thu, Mar 23, 2023 at 2:56=E2=80=AFPM Matthew Wilcox wrote: > > > > On Thu, Mar 23, 2023 at 12:07:46PM -0700, Hugh Dickins wrote: > > > On an earlier audit, for different reasons, I did also run across > > > lib/buildid.c build_id_parse() using find_get_page() without checking > > > PageUptodate() - looks as if it might do the wrong thing if it races > > > with khugepaged collapsing text to huge, and should probably have a > > > similar fix. > > > > That shouldn't be using find_get_page(). It should probably use > > read_cache_folio() which will actually read in the data if it's not > > present in the page cache, and return an ERR_PTR if the data couldn't > > be read. >=20 > build_id_parse() can be called from NMI, so I don't think we can let > read_cache_folio() read-in the data. Interesting. This being the same Layering_Violation_ID which is asking for a home in everyone's struct file? (Okay, I'm being disagreeable, no need to answer!) I think even the current find_get_page() is unsafe from NMI: imagine that NMI interrupting a sequence (maybe THP collapse or splitting, maybe page migration, maybe others) when the page refcount has been frozen to 0: you'll just have to reboot the machine? I guess the RCU-safety of find_get_page() implies that its XArray basics are safe in NMI; but you need a low-level variant (xas_find()?) which does none of the "goto retry"s, and fails immediately if anything is wrong - including !PageUptodate. Hugh ---1463760895-38525656-1679623005=:6497--