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 209D0C5CFE7 for ; Tue, 11 Aug 2026 16:51:53 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 1B0EE6B007B; Tue, 11 Aug 2026 12:51:52 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1891F6B0095; Tue, 11 Aug 2026 12:51:52 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0545C6B00A9; Tue, 11 Aug 2026 12:51:52 -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 CCD766B007B for ; Tue, 11 Aug 2026 12:51:51 -0400 (EDT) Received: from smtpin22.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 6410D40128 for ; Tue, 11 Aug 2026 16:51:51 +0000 (UTC) X-FDA: 85089580422.22.D2BE91C Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf27.hostedemail.com (Postfix) with ESMTP id CD85B4000D for ; Tue, 11 Aug 2026 16:51:49 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Zu6P4EWl; spf=pass (imf27.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 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=1786467109; 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=nUtXloIWo+60BaXIYhpidIQX8u9D+3kedoVN7C9D9/g=; b=TZpaXPCKC5nqhttJ3I8IYUuZNV5E7q3dFD3r+skvsFD4Aui2vPILZ/QlSNBbPXdQNOossw /R//WX76avxWdPZzxkdJEUeeR9Qmaye6oZcu4bFnr6D9OG8/rfGz6T7w5yJvC62onUDItZ 8RY3jsPw9vfWHftkYLL5cUO13c+dVUg= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Zu6P4EWl; spf=pass (imf27.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1786467109; b=wAeo2q6U37MWyrfQMuJCfBPOHAYHS1eLLyBHH5Q72zVd6hti4i1TSkBo+3uvEr5/Wv5dCl pYerQX9tFpPScvgpS6eDepY89RpXoAg2MlAMDPQPpaSXg0B8nLNWvUuQ28Sqrd0IY8Dvtg jJ45iRJPkjEsSKg5n+IbPetZK0c3gUU= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 66C52600AD; Tue, 11 Aug 2026 16:51:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 694BD1F000E9; Tue, 11 Aug 2026 16:51:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786467109; bh=nUtXloIWo+60BaXIYhpidIQX8u9D+3kedoVN7C9D9/g=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Zu6P4EWld4gpzY1R8hq3ER5DyVSS8EQG3tj3hB0FUUqztpnB1xSYcKl3Q43tc8cmj UUsHVaeqqzm48VuQVJJx2EmW7mni8RQ6I1+levHRzt5ChDbHMTxJyaxCh3f6iBS0/C 55H0zKXQaRRXxQd/+WCqvaxpLr5pPGlTLRkmGM/8141rUWlck+hHndDPdyOG2aaDBw gO3sp1uV5pzP/Ne9Y0kFwRhkfkxbs6cWxO90fh/uBbI39rSVBYq65rSukH7lNfLsuz C2uETEK6ptuNat6DVNihDE0Y6C1cj1icY2cXtTTklAMhkklLMENnIaGg5NMBUxP04U D1oeyGwJyciyA== Date: Tue, 11 Aug 2026 17:51:33 +0100 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (Arm)" Cc: Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , "Matthew Wilcox (Oracle)" , Jan Kara , Miaohe Lin , Naoya Horiguchi , Rik van Riel , Harry Yoo , Lance Yang , Kees Cook , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Usama Arif , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Peter Xu , Xu Xin , Chengming Zhou , Arnd Bergmann , Greg Kroah-Hartman , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Sven Schnelle , Alex Deucher , Christian =?utf-8?B?S8O2bmln?= , David Airlie , Simona Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Boris Brezillon , Steven Price , Liviu Dudau , Huang Rui , Matthew Auld , Thomas =?utf-8?Q?Hellstr=C3=B6m?= , Rodrigo Vivi , Masami Hiramatsu , Oleg Nesterov , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , James Clark , Jason Gunthorpe , John Hubbard , Muchun Song , Oscar Salvador , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Youngjun Park , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org, linux-s390@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, intel-xe@lists.freedesktop.org, linux-perf-users@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH v4 07/20] mm/vma: fix self-merge check in copy_vma() Message-ID: References: <20260806-b4-scalable-cow-virt-pgoff-v4-0-ab318a350404@kernel.org> <20260806-b4-scalable-cow-virt-pgoff-v4-7-ab318a350404@kernel.org> <3a0a9aaf-20f5-4f92-b848-00ab702e8fe2@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3a0a9aaf-20f5-4f92-b848-00ab702e8fe2@kernel.org> X-Stat-Signature: hydw8f943ssm9rh8bwuzhi6uxxo7fbzy X-Rspamd-Queue-Id: CD85B4000D X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1786467109-739412 X-HE-Meta: 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 w2GmOfxW wlkc2GuWeMeOg3Ij6dVJ7YPaTEX3JcHvAtNYrm9jJwfAVPGrmvTIIFHQG4wBV9+JKy2oFPUig3F/YDb2KwiVoj5CW0Pg2ybmNgrCwiYCkFXnwIAspyx/5jJ1t5vLfu7IaO+OztZdk7+x8GLjp/e0Q5FIfAYpYpbYD4nES7J4um0U98DFYN0D6AI0NAXJlZqFSDI5mHdUtEp/9c5PmzEArRalfRfnNWkRa7T4OsOYpgjMuut0Inlo78ja4yrlX+2Hkrz/0qvgmniXsYRj6Z9SpiDcAh5slMs93tVmNtZG4UT2TU0tl/W4B/eyBkxvVC1j2w/u7AU8z+pRI/5mJYoXU90n6DYqnkK6BKDkaALEajJn8kmKtT1B8pPES33WaspbKsTnnvzlkshsrjIE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Aug 11, 2026 at 06:44:01PM +0200, David Hildenbrand (Arm) wrote: > > > > Since copy_vma_and_data() which calls copy_vma() intends to reference the > > old VMA after the merge, it must have this pointer updated. > > > > This kind of self-merge is not possible with a succeeding merge, as the > > merge always prefers to expand the preceding VMA if possible. > > > > copy_vma() accounts for this by explicitly checking to see if a self-merge > > occurred and updating the vmap pointer if so. However it incorrect did so > > even for a subsequent merge (this is simply a noop so it had no impact). > > Took me longer than it should to find out that this is no real fix ;) > > > > > So change this to only check for the case which matters - a backwards > > merge - and rearrange the parameters to make it clearer we're doing that - > > i.e. check new_vma->vm_start < old_vma_start (having already renamed > > vma_start to old_vma_start to make it clear this is the previous VMA). > > > > Also update the existing wall-of-text comment to be a lot clearer. > > > > While we're here, replace the VM_BUG_ON_VMA() with a VM_WARN_ON_ONCE_VMA() > > and update the VMA userland tests accordingly. > > > > No functional change intended. > > > > Signed-off-by: Lorenzo Stoakes (ARM) > > --- > I skimmed over it, looks correct, but the merging stuff is way over my head to > confidentially give a RB tag her :) Well that's what A-b is for ;) > > -- > Cheers, > > David -- Cheers, Lorenzo