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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 77FF4C43458 for ; Sun, 12 Jul 2026 08:54:07 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 591206B0005; Sun, 12 Jul 2026 04:54:06 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 51BAA6B0088; Sun, 12 Jul 2026 04:54:06 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3E4FA6B008A; Sun, 12 Jul 2026 04:54:06 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 180986B0005 for ; Sun, 12 Jul 2026 04:54:06 -0400 (EDT) Received: from smtpin21.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 95CCA4085C for ; Sun, 12 Jul 2026 08:54:05 +0000 (UTC) X-FDA: 84979512450.21.7DCE6AB Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf19.hostedemail.com (Postfix) with ESMTP id 0A6701A0003 for ; Sun, 12 Jul 2026 08:54:03 +0000 (UTC) Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=epPcl9sY; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf19.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1783846444; b=npGT23vVbkvht98m2MQOoKBPmlxIHnS0Q24XtNsyrOM+rO8QfzUuetcTUYi/uC35AeE+Rj j9Rfg+veSH8EhrFzNxP5mpFFcJL96YdAfAKxChbJQh9rA5vM96fCJFdvEQ8P4qryzFPISi cxX+ckdddNBaEJRqB/v2s+6XU6ZHhnk= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=epPcl9sY; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf19.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1783846444; 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=GnL9C72NCuP+8WoVaUMRNhlRZdNBSwfW36nJtkAt9LI=; b=cst5MrhDYp1EELP4ufERbEvq53sKFbzf6CHzw3Zt2DQM00BMBmJxbiHo9FoIsGx91cMMJb B9ETWj7fTFBXf4ahSJMAx/rfDcjKC7MtQ+hj+qVHgF5AZjQ+sg/ZGKXX1EyoOVIJG1moC+ ppwWs02nzpdBAq88zE3hoLDhhCey9cg= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 6A8CB600AA; Sun, 12 Jul 2026 08:54:03 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1958B1F000E9; Sun, 12 Jul 2026 08:53:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783846443; bh=GnL9C72NCuP+8WoVaUMRNhlRZdNBSwfW36nJtkAt9LI=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=epPcl9sY5qVsxQZgyUPrZsLn7kXboM/IbScY0npRmn9P+uRRsG+P7J04YR+iaTObs 1Px8rtHkErijBwOPBiUblVWwHivtzui7iKOQzLnQCbfVUWTosHxOMF+GGFijea9wlK zbz39L341j03oPz2WAoRaPtTJh2riBYK1+pzbZ//v7p4o3QWUPlAcJ0yDZ/ZtLH2I3 oCr2y9pF59kfYfOJFdkWO49UwMw4GcYox72kxTR4mDa4FbEoXG2CkFx8yZYdAjkTL3 E6oDW4BUgoGmtZEjVpvqLSM6YwBYEbG5gElIdhTpYK4nxTZEhlk/ORnJAQa2ENgvoc w58yTf35cMoSg== Date: Sun, 12 Jul 2026 09:53:48 +0100 From: Lorenzo Stoakes To: Mike Rapoport Cc: Andrew Morton , David Hildenbrand , "Liam R. Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Toshi Kani , Catalin Marinas , David Carlier , Dev Jain , Ryan Roberts , Shakeel Butt , Will Deacon , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] mm/ptdump: always stabilise against page table freeing using init_mm Message-ID: References: <20260710-b4-fix-non-init_mm-ptdump-v1-1-2d40982c98ec@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 0A6701A0003 X-Rspam-User: X-Stat-Signature: waza8cbjf7n8o7efb1x89khsfgxam8fd X-Rspamd-Server: rspam03 X-HE-Tag: 1783846443-703683 X-HE-Meta: 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 aG4bxUnV dSSjvN7kyp8nx+ycq62wbYwtmqkhPE4k1be1eT4Q8Yv9C3U118U6lko0PlT3Zd1WritNU8bs+EkXLhS0xuFdoDfzPYVrASCV3ZDjB/f5+BmdPRkOsY+8Af8v7ioJu244nKtdujRXxVgKXrOHMTbmlJRB/r5Akta7wtgpVuKlc9HPjyjFXxcwJ2pt4YGd3JpAWPbNXyk2w1Fu4aqDqNQItcPdHdsQRainoI3FFHBhLJVz6Dw26xftIV50gtg9tV+JZfBB8lhD/q+K6Z0V4NkL8EKSwLBDf9SSnOhDemVL3koNr1O/Aqf2g9o2zsVPBXoq+ONha Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Jul 11, 2026 at 01:08:46PM +0300, Mike Rapoport wrote: > On Fri, Jul 10, 2026 at 02:29:21PM +0100, Lorenzo Stoakes wrote: > > x86 and arm64 invokes ptdump_walk_pgd() with non-init_mm mm whilst still > > Nit: ^ invoke > > > walking kernel page table ranges. > > > > For x86 this is done in ptdump_curknl_show() and ptdump_efi_show(), the > > first passing current->mm, and the second passing efi_mm (we reach kernel > > mappings that init_mm protects for current->mm due to x86 cloning shared > > kernel page tables for arbitrary mm's). > > > > arm64 does so via ptdump_debugfs_register(), configured by efi_ptdump_info > > for efi ranges against efi_mm. > > > > The init_mm mmap lock is used to stabilise page table freeing against > > ptdump, so take a nested lock on init_mm to ensure that we are correctly > > stabilised. > > > > We take this after mmap write locking the non-init_mm mm. Nothing acquires > > the init_mm lock first before locking an arbitrary mm, so no deadlock is > > possible. > > > > Other fixes have been sent which update the two cases which can cause races > > with ptdump in init_mm ranges to acquire the init_mm mmap write lock - vmap > > and x86 CPA huge page promotion. > > > > For arm64, commit fa93b45fd397 ("arm64: Enable vmalloc-huge with ptdump") > > already provides exclusion against init_mm for the vmap case, which this > > patch also pairs with. > > > > The first point at which ptdump can race kernel page table freeing is > > commit b6bdb7517c3d ("mm/vmalloc: add interfaces to free unmapped page > > table"), so we target this in the Fixes tag. > > > > Fixes: b6bdb7517c3d ("mm/vmalloc: add interfaces to free unmapped page table") > > Cc: stable@vger.kernel.org > > Signed-off-by: Lorenzo Stoakes > > > > --- > > mm/ptdump.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/mm/ptdump.c b/mm/ptdump.c > > index 973020000096..6bef47b1a073 100644 > > --- a/mm/ptdump.c > > +++ b/mm/ptdump.c > > @@ -178,11 +178,18 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd) > > > > get_online_mems(); > > mmap_write_lock(mm); > > + /* To stabilise page tables we must hold the init_mm lock too. */ > > Maybe > > /* To stabilise kernel page tables we must hold the init_mm lock too. */ > > Other than these nits Ack on nits will fixup on respin. > > Reviewed-by: Mike Rapoport (Microsoft) Thanks! > > -- > Sincerely yours, > Mike. Cheers, Lorenzo