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 ED1E849482C for ; Mon, 14 Sep 2026 15:09:38 +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=1789398582; cv=none; b=HR3+4+4ljnFplCkNkE7Owvg3s90o2QQa9R9qK/s2P9QVAhAlzclj8HJt6VQjg7W1J3cvDR6++vssyABLRU9kzgJE6WBw2+F8Y3v83jwDmOxpcHtZHAL/gy4yJGTQycpegaclz6IN7CRxyoBVK407ma+Ti14SizV2oeV2Ox+Xxwo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789398582; c=relaxed/simple; bh=h5eD1Irq6YzOfG2HRbwOK54UqLD3Mz80nj7cCYaJSyw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=cYz8Zn1dpP9F7ZrVJXdZ7dHVkgYkeiWWx4c56uunXWhgmhaTuqLgWCjunEbJIZC4JZb9EFD7u1TeuDtFvqI7AhItUgEemoLMg6KsFGXcELrwIC0trgmLSqRrKrcy6hpU6YZ/1TnNIcIj/ULDEHhKNWZNF513Qjm7MjgCE8RJx28= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WcXlyuz1; 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="WcXlyuz1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 977821F00893; Mon, 14 Sep 2026 15:09:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789398578; bh=lqGx/g9iA8NHnrHaYC5eHMoZQvuNCtTEzYjoeYtI/wc=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=WcXlyuz11wuqXhEOE712pccfVCodWo1JsYcoBXEU8WVlNcItPfa55fFiROejw8tRc lnRyISQ+aGw/9Eu1iMx9m5Sz0OBNXExpG1C5jO4S7y9zwOZdc7/HTjiUQFuzxlCaOi TjrBvGod2FRnfM5IPUQnh7vGEVUM0PZz9IfEAst+SEn3L+E3E+OseVETV7mzFUEz0s PK0MKuMS7TkGj69J3pvFrRn044ZLSeww4P3RP2RtP7+iTHFGyKTkyb9OzU4Vsj4kDu fUKabYFlTOaXP3yQ6jW7qe20XnUpy8gLuWo6PiffhTiPTbtvvQaW7wVUKEHL/PY5Bo I5rCdMRmTRguQ== Date: Mon, 14 Sep 2026 16:09:27 +0100 From: "Lorenzo Stoakes (ARM)" To: Pedro Falcato Cc: Andrew Morton , Suren Baghdasaryan , "Liam R. Howlett" , Vlastimil Babka , Shakeel Butt , David Hildenbrand , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Mike Rapoport , Michal Hocko , Xu Xin , Chengming Zhou , Jann Horn , 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> 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: On Mon, Sep 14, 2026 at 03:24:47PM +0100, Pedro Falcato 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. > > > > 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. > > > > v1: > > https://lore.kernel.org/r/20260909-vma-is-faulted-v1-1-3a701f48984a@kernel.org > > --- > > include/linux/mmap_lock.h | 12 ++++++------ > > mm/huge_memory.c | 4 ++-- > > mm/internal.h | 2 +- > > mm/khugepaged.c | 3 +++ > > mm/ksm.c | 10 +++++----- > > mm/madvise.c | 4 ++-- > > mm/memory.c | 2 +- > > mm/mprotect.c | 2 +- > > mm/mremap.c | 4 ++-- > > mm/rmap.c | 22 +++++++++++----------- > > mm/swapfile.c | 2 +- > > mm/userfaultfd.c | 2 +- > > mm/vma.c | 29 +++++++++++++++-------------- > > mm/vma.h | 22 +++++++++++++++++++++- > > tools/testing/vma/include/dup.h | 2 +- > > tools/testing/vma/include/stubs.h | 4 ++++ > > 16 files changed, 77 insertions(+), 49 deletions(-) > > > > diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h > > index 00eae65b74bd..03e1eb136111 100644 > > --- a/include/linux/mmap_lock.h > > +++ b/include/linux/mmap_lock.h > > @@ -273,7 +273,7 @@ static inline void vma_end_read(struct vm_area_struct *vma) > > vma_refcount_put(vma); > > } > > > > -static inline unsigned int __vma_raw_mm_seqnum(struct vm_area_struct *vma) > > +static inline unsigned int __vma_raw_mm_seqnum(const struct vm_area_struct *vma) > > { > > const struct mm_struct *mm = vma->vm_mm; > > > > @@ -288,7 +288,7 @@ static inline unsigned int __vma_raw_mm_seqnum(struct vm_area_struct *vma) > > * > > * Returns true if write-locked, otherwise false. > > */ > > -static inline bool __is_vma_write_locked(struct vm_area_struct *vma) > > +static inline bool __is_vma_write_locked(const struct vm_area_struct *vma) > > { > > /* > > * current task is holding mmap_write_lock, both vma->vm_lock_seq and > > @@ -344,7 +344,7 @@ int vma_start_write_killable(struct vm_area_struct *vma) > > * vma_assert_write_locked() - assert that @vma holds a VMA write lock. > > * @vma: The VMA to assert. > > */ > > -static inline void vma_assert_write_locked(struct vm_area_struct *vma) > > +static inline void vma_assert_write_locked(const struct vm_area_struct *vma) > > { > > if (!IS_ENABLED(CONFIG_MMU)) { > > mmap_assert_write_locked(vma->vm_mm); > > @@ -359,7 +359,7 @@ static inline void vma_assert_write_locked(struct vm_area_struct *vma) > > * lock and is not detached. > > * @vma: The VMA to assert. > > */ > > -static inline void vma_assert_locked(struct vm_area_struct *vma) > > +static inline void vma_assert_locked(const struct vm_area_struct *vma) > > { > > unsigned int refcnt; > > > > @@ -410,7 +410,7 @@ static inline void vma_assert_locked(struct vm_area_struct *vma) > > * With lockdep disabled we may sometimes race with other threads acquiring the > > * mmap read lock simultaneous with our VMA read lock. > > */ > > -static inline void vma_assert_stabilised(struct vm_area_struct *vma) > > +static inline void vma_assert_stabilised(const struct vm_area_struct *vma) > > { > > /* > > * If another thread owns an mmap lock, it may go away at any time, and > > @@ -445,7 +445,7 @@ static inline void vma_assert_stabilised(struct vm_area_struct *vma) > > vma_assert_locked(vma); > > } > > > > -static inline bool vma_is_attached(struct vm_area_struct *vma) > > +static inline bool vma_is_attached(const struct vm_area_struct *vma) > > { > > return refcount_read(&vma->vm_refcnt); > > } > > nit: I would suggest you do all of this constification in a separate patch, > otherwise it can become tricky for backports. Things can naturally start depending > on const correctness, and you either need to manually adjust those future patches, > or try to backport this one. Ok will break out. > > The rest looks vaguely good to me. I admit I'm not a gigantic fan of the name, > but I suspect it fits better with your future anon rmap ideas :) Naming's hard and it's hard to make everybody happy, unfortunately :( vma_has_anon_rmap() better? > > Reviewed-by: Pedro Falcato Thanks! > > > -- > Pedro -- Cheers, Lorenzo