From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id D1FDE606A88C for ; Sat, 14 Nov 2026 18:34:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=kLdIUvRD Received: by kanga.kvack.org (Postfix) id F277C6B05B5; Sat, 14 Nov 2026 13:34:34 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id ED8476B05B6; Sat, 14 Nov 2026 13:34:34 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DEF806B05B7; Sat, 14 Nov 2026 13:34:34 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id BB0BE6B05B5 for ; Sat, 14 Nov 2026 13:34:34 -0500 (EST) Received: from smtpin11.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 4D6C614045B for ; Sat, 14 Nov 2026 18:34:34 +0000 (UTC) X-FDA: 85434575268.11.F597AE1 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf20.hostedemail.com (Postfix) with ESMTP id 9DE821C0006 for ; Sat, 14 Nov 2026 18:34:32 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=kLdIUvRD; spf=pass (imf20.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1794681272; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=xIJH830yAU8Etb/lYqZfpJ4EsMpPggWMJX7lGP00TrM=; b=JJLg2FPgjoaY/DAbIhaARoSJ98UqcmVWWHFfbAs3nQvlw96VqTTrgRYv7LDWSlpa85GIVR 8vUJVlEjpzOlTy3m2AFOLbwe6DRWOvdWU9k3oUKg09A2PJi2TpcF0y0e1JHFpp7tJxzKh8 zGNlBaHva/NzDN/KlDOFmu65cF2AO0k= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1794681272; b=5ecr+hyA2e+dIA7pHp8f5y0ML0quyX2W/4LNSqK2700x9AFhcHB1wbptXmWwwJy3J26Mz/ 6mwR9782m7C0jdDrNF2T7libkTPGWyQk3WYs4pd5mVqEEDHJ1RftDXDbKQ3fZ29uTBEgby 3QvJBKEoXglmsRVWvXyu9EcMP/K1658= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=kLdIUvRD; spf=pass (imf20.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 9737842E8E; Sat, 14 Nov 2026 18:34:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CA86A1F000C4; Sat, 14 Nov 2026 18:34:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794681271; bh=xIJH830yAU8Etb/lYqZfpJ4EsMpPggWMJX7lGP00TrM=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=kLdIUvRDvJxlUbY1ynRLNC3qDVm22HDJQ/oDoeAj04J3VQf5GOK2z+EVYkFf54oeO ojMxnJJciIKBWDTf+n2auyLYOSEpUgnGR63WYG6R7v0ceX42IOP9B6sHO9PCtbaxqU 8FTFzMmpeWihgC5vIRFbUbZVoQJLQLQJ1FaYtUMWyWEvptvnftr8Gd8NEwSs/tjm4P IfryQo5zUxv5NMGHR4OmlosERhkQzHZgGtHy0jZYv0hXUSugT1jq3HrSUrJVoQAJ9j BHU7F3zmvwDZJSycFY0Uv4MQdEl6eRlTEvANgZi+rMgpityIDbYPWUvZR5PZlsfO2a LsMXcMZ02scMg== Date: Sat, 14 Nov 2026 18:34:19 +0000 From: "Lorenzo Stoakes (ARM)" To: Mika =?utf-8?B?UGVudHRpbMOk?= Cc: Balbir Singh , David Hildenbrand , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , David Rientjes , Shakeel Butt , Andrew Morton , Jann Horn , Pedro Falcato , "Matthew Wilcox (Oracle)" , Jan Kara , Nhat Pham , Johannes Weiner , Zi Yan , Matthew Brost , Joshua Hahn , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Usama Arif , Kairui Song , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Kiryl Shutsemau , Yu-cheng Yu , Dave Hansen , Dennis Zhou , Tejun Heo , Christoph Lameter , Peng Fan , Josef Bacik , Chris Mason , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, "Borislav Petkov (AMD)" , Mark Brown , "Dennis Zhou (Facebook)" , Rick Edgecombe , Josef Bacik , stable@vger.kernel.org Subject: Re: [PATCH v2 05/13] mm/migrate_device: don't collect a range twice Message-ID: References: <20261113-mason-migrate-et-al-fixes-v2-0-50a2ed382b61@kernel.org> <20261113-mason-migrate-et-al-fixes-v2-5-50a2ed382b61@kernel.org> <8c79ce88-7730-44c4-92a0-d760d6f8e9e1@redhat.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8c79ce88-7730-44c4-92a0-d760d6f8e9e1@redhat.com> X-Rspamd-Server: rspam06 X-Stat-Signature: kggpnp3x3tzaptbkdc8dx9dhezuckm8m X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: 9DE821C0006 X-Rspam-User: X-HE-Tag: 1794681272-648331 X-HE-Meta: U2FsdGVkX19zVg3EQ+Rzm41hukC6eT8QTq8+keJSEi6jFSGTTu6ATQgXi0W3QxxobO2HwCWFT24FRJSADdHN4CdVEv3fo8+YHulV+mEJ2sY+kQP4YXcEpv5HQmcqcYXLJwFJSVjQ4rgYo1UAjQZgNmxeuoawCZc0uBban+6BNe04P6TTPj3A1GsJAgin2AJhJnaipvCSAlmXtrcs2PBmBz90+cIj4SqLNlyYnDxlSVebnPz56iMN1gVuiKI4aYnIwtF/NAPiATp2hzfvwKXzcbp2jovJ9PLkttVE1Q0eO0ahbM9dg68Q5a+gIbmx0PW0tCJZmZNSPtzuz1YEjQa4y0VhX+WCGhOs3qS5pE6kch6iyONufy7wLk5+jo2nbvp+kxJIX66nBK0M4zZD5NXmkcLkGhrHH4Q17B/WJCtf1B8uy7PqhGTXaZmpsrluLwZNICeH3xldNMfurZXXBWNKt6wgShZPj0l/VQ97uMgn5ZyQlh2/v3SgdKFzyY065RFGRi5D6NGxlRODL8zcdKxxFaQHhPH2H05oKtuiD0IGWkRRrIsnzzAIgF7MN6vWKA0BEx9isBiSMuib9Z08JX4fTJG+APsfXScLRmSd6sFLf4LAhEirixiu1MZHAZzCz4K/aUB00AsTKTL1XjgTJdsV5oBYKk3bciObM/2z++fyKCBvxzHjuaoaLbDaSXJ/CvPePCjqPIbivCqefvhS9MP01N5u8VOajCr6SJ7i2XZzVhvnpsijFLmPHR//DQWsRpsBfUCfiGR41+DG3jroPPOsH/rya/QjCrmuLtWbqsfgB+LOYBd1Ql2u5gkfEI2rSApRBo3yCnvYmBt++1FgJnfZ6xscG1k18FvvJ5OElXp+K/o5hPvxg5Lhv0pEA07fmYZ0wjc2GCnK6xiKMc1yO5ey1L/kwoxApjnW2CTIzkVQt9Zv29ilsqnzBcUM83yMcLJr52JTyLDJ5SCmVfGczU0 wNMDM2Da 6V8oF1TNo05LQ8L5oQxIkyCHT1v+pa/SLoq/S9ngJCRC5LNX0k1mMFFdd3tvtHeS3MZz5HzBF4nhau7DvoUOwgEPAcyFiweR+uTwW6aBHN4+pBTjhalAYMsa4C2FkhJ308pmpREXXYBf1u7oQrLGQs7ZnhJR7VvoOSGFHP1K9MwFKED4cSVQ9vCZMYTmmbEB+WeQdFf5I2ArDwoKtLt1Pe8I+8iCjDkxtHyZ5QrJaxOfBNkNs+8ddbAbGB5EASMIvfTIVc+MybqpptdBwE5dKEf6MuLrL+hpTTVTAJYLexagPW7bl4K4A+lxnVm+wRYwwP//oU3a8JiNPycsV0K/GV4GfA581LJcgwTbI5c5zqUAdDPPs8QuR89BW5e/V+GMDZ/cVvHKbUo2O3ZOs320E0O5dIA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Sat, Nov 14, 2026 at 08:45:55AM +0200, Mika Penttilä wrote: > On 11/14/26 07:09, Balbir Singh wrote: > >> diff --git a/mm/migrate_device.c b/mm/migrate_device.c > >> index 9e5dab8e1b77..28ed706109da 100644 > >> --- a/mm/migrate_device.c > >> +++ b/mm/migrate_device.c > >> @@ -257,13 +257,17 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > >> pte_t *ptep; > >> > >> again: > >> + /* [start, addr) is collected if we get here after splitting a folio */ > >> if (pmd_trans_huge(*pmdp) || !pmd_present(*pmdp)) { > >> - int ret = migrate_vma_collect_huge_pmd(pmdp, start, end, walk, fault_folio); > >> + int ret = migrate_vma_collect_huge_pmd(pmdp, addr, end, walk, fault_folio); > >> > >> if (ret == -EAGAIN) > >> goto again; > >> - if (ret == 0) > >> + if (ret == 0) { > >> + if (unmapped) > >> + flush_tlb_range(walk->vma, start, end); > >> return 0; > >> + } > >> } > >> > >> ptep = pte_offset_map_lock(mm, pmdp, start, &ptl); > >> > > Is the intended race a concurrent MADV_DONTNEED reclaiming the PTE table while > > PTL is dropped for the split? That would leave pmd_none() true on retry, entering > > migrate_vma_collect_huge_pmd() through !pmd_present() and taking its hole path. Balbir - yeah exactly the PTE page table removal, and it zaps the migration entries installed for [start, adr) too, so those don't keep the table alive. And yeah, we would then see pmd_none() on retry and migrate_vma_collect_hole(start, end, ...) would appends entries on top of those already collected. > > I think this is "ok" for the fix, the hole is collected from [addr, end). Thanks. Yeah addr > start, so it's not PMD-aligned so always ends up in the per-page path. And if the split happened at the first entry then nothing is collected yet anwyay. > > But couple of things follow. It can't be possibly collected as > MIGRATE_PFN_COMPOUND entry, only small pages. And the collected entries > in [start, addr) are wrong ones.  Finalize will recover, but the > migration will fail for those. But that's true for any zap that races after collection started, so there's nothing for this fix to do here. > These all are handled in the HMM walk based migration series. Ack great glad to hear :) -- Cheers, Lorenzo