From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 43C8249F11A for ; Thu, 17 Sep 2026 09:48:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789638527; cv=none; b=L9IB10mtHcupv3TF8j17rNeqigNvEehGgCFN4U0Kcm3Nlr1FlD9P56iCmCM/8FMuUJHgnjlqiifkwCDNoUpYonWfUhnk/9Fr+MVkqH8oCGBAK59spT7VfpjJq4Qc47Gt3ptGcj+8TrUPui7Bog/DHMAGAfPfEu3nF1zuunfwcX8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789638527; c=relaxed/simple; bh=cvbrrCjlcJUDVupgfBYiXkVaVkcnO7ArmWsB4gBXvVQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=DQxMp42tbPsld4sqVd6+Szuzwu88WmNwKPpUe1NdnR6H2nSBI62rjgxgFlH4YEcpPdIfVBh702LfWnoUbzxjK7rOARBoPSNvBcppkKgVgUrbtHJYlC+1LlQBwcGcolpU9xE4o86WAf3p9GMrNHa8FOggzCJ6hhgudr5WKIl9uM8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RXQbRdQb; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="RXQbRdQb" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A58101F000FF; Thu, 17 Sep 2026 09:48:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789638509; bh=SSQlyaKBFOXmjTXXwb4CnAc04mzkW2ufkK1lWWnGyPE=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=RXQbRdQbaMBgU589o6W6PG3uphqN8mz/5BLM7kb4FOOK2HUFAR93FxbAoJTEAO8Bu eBoMaio317U16mMAW0vaD84KGV27INu10hhQohZWaKuKgfSOO3qZzptjmllqY/CUt/ IuuDdJMQ0mKaF3URDpMUpD2v9wmA5TOXdERqKfg6G4aBNbU+E4K218mD0RumAFV1Mt COnZBQ1CMqCB/u9P+dkXryFycmkanLLTAJtGqNyQEtHTufZKXMU081Bw99vgtS9b0W qM4li9bj33ALeGiPbwdYhg9T2fzZ9DGvn14y4LfOgNz2xVrwZu3cOup4lJ6KfrLH9o JwkgKTsO8Aq7Q== Date: Thu, 17 Sep 2026 10:48:17 +0100 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (Arm)" Cc: Kiryl Shutsemau , Andrew Morton , Suren Baghdasaryan , "Liam R. Howlett" , Vlastimil Babka , Shakeel Butt , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Mike Rapoport , Michal Hocko , Xu Xin , Chengming Zhou , Jann Horn , Pedro Falcato , Rik van Riel , Harry Yoo , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Youngjun Park , Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Guilherme Giacomo Simoes Subject: Re: [PATCH v2] mm: implement and use vma_anon_tracked(), silence KCSAN Message-ID: References: <20260910-vma-is-faulted-v2-1-e81ebc7d146b@kernel.org> <4b2c99f6-d7c0-42a2-bf9a-e85061d53c93@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4b2c99f6-d7c0-42a2-bf9a-e85061d53c93@kernel.org> On Thu, Sep 17, 2026 at 11:45:12AM +0200, David Hildenbrand (Arm) wrote: > On 9/14/26 17:21, Lorenzo Stoakes (ARM) wrote: > > On Thu, Sep 10, 2026 at 02:50:25PM +0100, Kiryl Shutsemau wrote: > >> On Thu, Sep 10, 2026 at 02:18:35PM +0100, Lorenzo Stoakes (ARM) wrote: > >>> Provide a function to abstract the common task of checking whether > >>> a VMA is faulted in or not. > >>> > >>> A VMA or mmap lock must be held when calling this function. For an attached > >>> VMA the transitions between unfaulted/faulted state are: > >>> > >>> Transition | VMA/mmap Lock state > >>> ------------------------|----------------------------------------------- > >>> unfaulted to faulted | write lock OR read lock + mm->page_table_lock > >>> faulted to unfaulted | write lock > >>> > >>> So vma_anon_tracked() never provides a false positive (the lock precludes > >>> it), but if only a read lock is held, a negative result must be re-checked > >>> with mm->page_table_lock held. > >>> > >>> Detached VMAs cannot be concurrently manipulated as they are removed from > >>> the maple tree so require no guarantees. > >>> > >>> Use data_race() to silence KCSAN about non-existent data races between > >>> concurrent vma->anon_vma read/write on optimistic fault tests. > >>> > >>> Also while here, const-ify vma_is_attached(), vma_assert_stabilised() and > >>> dependants. > >> > >> If you end up respinning anyway, this would be a natural separate > >> prep patch. > > > > Yup will do, Pedro also asked for this! > > > >> > >>> Finally, update the core VMA merge/split, rmap, mremap, KSM and fault > >>> preparation callers which test vma->anon_vma directly to use > >>> vma_anon_tracked() instead. > >>> > >>> Note that the lockless read in reusable_anon_vma() is doing more than > >>> checking whether the VMA is faulted - it is returning the anon_vma to be > >>> used on fault, so this check is not altered. > >>> > >>> There is one odd one out - file_backed_vma_is_retractable() - which holds > >>> neither a VMA nor mmap lock and is stabilised by the file rmap lock only. > >>> > >>> Therefore just add a comment to explain why the direct vma->anon_vma check > >>> is required. > >>> > >>> Reported-by: Guilherme Giacomo Simoes > >>> Closes: https://lore.kernel.org/all/20260829100034.423064-1-trintaeoitogc@gmail.com/ > >>> Closes: https://lore.kernel.org/all/20260909115723.528501-1-trintaeoitogc@gmail.com/ > >>> Signed-off-by: Lorenzo Stoakes (ARM) > >>> --- > >>> v2: > >>> - Renamed vma_is_faulted() to vma_anon_tracked() as per David. > >> > >> I don't particularly like vma_anon_tracked(), but naming is hard... > > > > Yeah it was a compromise because David and I disagreed on naming (again ;) > > > > I think vma_has_anon_rmap() is a better compromise? > > Yeah let's go for that. Ack will do thanks! > > -- > Cheers, > > David -- Cheers, Lorenzo