From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 C5E4632F759 for ; Wed, 1 Apr 2026 10:52:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775040743; cv=none; b=VMSjg5v1DO7YWTpojtqLML1AJQH4mchmK/x+AKRkbok/41LDmEA5sPCEziKAf42R6BowV02edKIrQmelFUDhvDT7LvvW9IXL/6YSI/8iHY04HLE+1TsfA49MegUq/dA1QcIcmMs7TmSoEaFy78caJTBRIidagK6u8mcnCrB4gko= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775040743; c=relaxed/simple; bh=7eNw3TxRt2f7CALy41ojguRmYDMXKZ+2KH/2ZcV1NOs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GAEqSv6RNiMy7gV9/GqV6u9ObPsN4STDnApDGZdxB+DCE2UGbXkYiFMUDhuPiL7Auy7RJNN5lpcnwQmy1hKZtUr6a0yI9v2LWhdD2zSnIO8MihTfL5mp+/EN7fTQNO5sAiBDeW5ugPTjjWfbChdTKIy4hHI4uw37+wQFV/GNLyw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Dru08UI0; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Dru08UI0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2699BC4CEF7; Wed, 1 Apr 2026 10:52:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775040743; bh=7eNw3TxRt2f7CALy41ojguRmYDMXKZ+2KH/2ZcV1NOs=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Dru08UI0SlP+Zwr0Te9QbJF+/b46qG2ViXXUiJYjswDkYhjhSWdbmpJXK7G1WHlkD 6di7HCe5TFwgqXb+Ge0z4hdZnhdpK68ez7YcCpurn5ZWoryFnp4cKUX6jZqlmR4pmA 0TtgvpeaYYCg9D81Yo5gopS05svvPQGIv1YSyrFeLlSajQ3GFxf0ITZPT+KcVXniS3 pDXGxjWW4kHhTkBJb33IddJvGYDMrQQ8l11VHigcsqW8SCPjDi7NsU+7dOmfR6mvah 4ZG19BEuNK+xRB/jZQWYBIZ6bzuvJN33/FKM382xZ+ynvXr8YRAgTVt/fDrTsGXtXJ 33ow31PSjJAew== Message-ID: Date: Wed, 1 Apr 2026 12:52:17 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: update stale locking comment in do_anonymous_page() To: Aditya Sharma , linux-mm@kvack.org Cc: akpm@linux-foundation.org, ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-kernel@vger.kernel.org References: <20260331142936.229667-1-adi.sharma@zohomail.in> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260331142936.229667-1-adi.sharma@zohomail.in> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/31/26 16:29, Aditya Sharma wrote: > The comment above do_anonymous_page() dates back to 2005 and describes > the pre-per-VMA-lock world where mmap_lock was always held on entry. > Since CONFIG_PER_VMA_LOCK was introduced (6.4), the fault handler now > has a fast path that enters holding only a per-VMA read lock, with > mmap_lock not held at all. > > Update the comment to describe both entry contexts accurately. > > Signed-off-by: Aditya Sharma > --- > mm/memory.c | 22 +++++++++++++++++++--- > 1 file changed, 19 insertions(+), 3 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index c65e82c86..cc8dbbaea 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -5210,9 +5210,25 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf) > } > > /* > - * We enter with non-exclusive mmap_lock (to exclude vma changes, > - * but allow concurrent faults), and pte mapped but not yet locked. > - * We return with mmap_lock still held, but pte unmapped and unlocked. > + * We enter in one of two locking contexts: > + * > + * 1) VMA lock path (FAULT_FLAG_VMA_LOCK set): > + * Entered holding a read lock on the faulting VMA (vma_start_read), > + * but NOT holding mmap_lock. This is the fast path introduced with > + * per-VMA locking (CONFIG_PER_VMA_LOCK). If this function cannot > + * complete the fault (e.g. needs to wait on I/O or encounters a > + * condition requiring the mm lock), it must return VM_FAULT_RETRY > + * and the caller will fall back to the mmap_lock path below. > + * > + * 2) mmap_lock path (FAULT_FLAG_VMA_LOCK not set): > + * Entered holding a non-exclusive (read) lock on mmap_lock, which > + * excludes VMA tree modifications but allows concurrent faults on > + * other VMAs. No per-VMA lock is held. > + * > + * In both cases, on entry the pte is mapped but not yet locked. > + * On return, the pte is unmapped and unlocked, and whichever of > + * the above locks was held on entry is still held (mmap_lock is > + * not dropped, VMA read lock is not dropped, rather, the caller releases it). > */ > static vm_fault_t do_anonymous_page(struct vm_fault *vmf) > { Was this AI generated? I don't think we want to have such a wall of text for each and every function that can be called with VMA lock or mmap lock in read mode. -- Cheers, David