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 348F1C43458 for ; Sat, 11 Jul 2026 10:08:59 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 251716B0005; Sat, 11 Jul 2026 06:08:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2030E6B0088; Sat, 11 Jul 2026 06:08:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 119956B008A; Sat, 11 Jul 2026 06:08:58 -0400 (EDT) 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 E47E66B0005 for ; Sat, 11 Jul 2026 06:08:57 -0400 (EDT) Received: from smtpin05.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 8588C1C8E67 for ; Sat, 11 Jul 2026 10:08:57 +0000 (UTC) X-FDA: 84976072314.05.414C8DD Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf20.hostedemail.com (Postfix) with ESMTP id DE34C1C0005 for ; Sat, 11 Jul 2026 10:08:55 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=GJR7iEPv; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf20.hostedemail.com: domain of rppt@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=rppt@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1783764536; 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=7h3aGld2owdMP9awF/sIZ0ZeSAhD+gvPs1e421zuh8E=; b=8Kfd39HXx68gxt5tnznJG1JybdKZCQI89Woa/FGBtZj/uRouiTlEXEuZZH+oiFMPnDZ442 f01nrdSZERlLQh3yhdFON2FyXL21sfC1S6dqB9YqQxQj0hGf4PXQm70cYgDqdoDjg2zfPM rBdzqaXGVJ6X1h7un3Zbx4yJQMUGSV0= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=GJR7iEPv; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf20.hostedemail.com: domain of rppt@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=rppt@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1783764536; b=oQo4NDuQhcxK3RVRqyhO8Ir47dI4hO5/ng3qmRNXZHzjIf5DMSwu1YPllzlVUJGNhC7e0Y rjlVgi+KCFRJzZi9XjXWqewNvCchdXv+nw8SS7ukOpIDEa9djiWWJdWz+IZvMcUKSR4jAg M2EBZ1MCa0+VvCZbR75eK5VoxiqeJYk= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id F1A8341247; Sat, 11 Jul 2026 10:08:54 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C51D81F000E9; Sat, 11 Jul 2026 10:08:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783764534; bh=7h3aGld2owdMP9awF/sIZ0ZeSAhD+gvPs1e421zuh8E=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=GJR7iEPvoOLeZDVwN8a/m8eQsstNeIf+B49TSqFKwMDzcFpMtF/YF/maBObxCalaC UUiaJvdi75QpJocaczvMAKnn9lGxyXeSYhgITG+bL8vXr99iad+Xvf3aDHHNhW/8H7 XsCm1q+bAukOUDEU06GDaWtlOaBP68l59MkJld1bcXlNBYkw6KxyMk5Bk7NcpXYziv seRHPaOcR7+s1L6tyyq0corRJWjWDsYWiJnZQtjT13c9BscneJ3M+3Pz8NgqFcyWEg 8XXsvxxQZsQDY6zq+tkoPbsYBz/LuJ2gDxWek8sIqPOB6M2riU7RIco5FskBQqWO/Q NP8eqdg37xZZw== Date: Sat, 11 Jul 2026 13:08:46 +0300 From: Mike Rapoport To: Lorenzo Stoakes 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: <20260710-b4-fix-non-init_mm-ptdump-v1-1-2d40982c98ec@kernel.org> X-Rspamd-Queue-Id: DE34C1C0005 X-Stat-Signature: 8au99tzp5i9e9qbjsn5nqjh1h6tcsogr X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1783764535-713637 X-HE-Meta: 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 5nPkDBfH ZeGgvrPw5eIPVm0dA2oCOvwWC5P03pFwEOn/Zsq3Hf8HVAXgNXnNxsiD/2vUy3AsB/91KMBOa0V9bTCCSfuienT1AefIKR5zi6VtTFxMLGDvREwYIThHqLD011twd1K1z4BiSRTTD/sDo/jf41ylp5nK1oxihaL+4KecbiAtSS4X3BbE5W+hTWvyOiWY5mhtPRYb4UFRnlJumJ/pkr92yPzYLB4owJCIblZtYu91xUhsQXukK48tQBhvt9T9h/CgW5yPi2smRx6VCjJ4JDkXDWLTe+llX5sygjkfYAbUG7Sy0Ue3dYikLPFmSreQ9AbktsWNk+PzPVx54bdc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 Reviewed-by: Mike Rapoport (Microsoft) -- Sincerely yours, Mike.