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 DF36531E826 for ; Thu, 23 Apr 2026 14:27:26 +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=1776954446; cv=none; b=d7HAGSGpGvX0GAl7q5XM+aSwGLeBzHiv8l+QKNORrJn7tZSRbn1xZFK+8i7tkKXV2aPmaWi7Yqs09JSrVyMCKR3lywK5dZUqG9AEw0EClc6QNFXHRsn3ILJY9mFXeFiHY4n/AZXUguO1roErL6bAsrjNSDlbffklNaiYEusd6bY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776954446; c=relaxed/simple; bh=2ZnCInGMmaglcEP4fiF1RXp7oGVSZVQ14PcgFK137SI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ESmyr9nqLIptpewKbejod9jB4zxMPTvkordJs7BI0qekDtz/h6Cpjj/G3vs0pbTLzCxv0VolX8kBUWHX0v7pZA0Ao49fDKOPHfZwSUr/4rVx/BlmpulfZYwniUEVsKvmp+5Gxfb7xKy3HXIDUBLrna+3HYmmOvmXshBY6ikXZiA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eCuQFsqX; 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="eCuQFsqX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EB172C2BCB3; Thu, 23 Apr 2026 14:27:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776954446; bh=2ZnCInGMmaglcEP4fiF1RXp7oGVSZVQ14PcgFK137SI=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=eCuQFsqX0RlSNvadGGdwqeOAq7SEK1GckH7LMbV7URFlMoYrKPKpCEyLLemHVFqQ7 vHvoaXG9YJe8+d5/wi5v25ybaLs6vJfcHKYBOyx3sF6d85do50FPIlwMxrCbczoYCb ZQCyOAYXAcw06cZVTttOgm5lN7JCuvuQLovkwLdWyw3pnT0L5ymykHGeUixiyQ7r8k exrr43zrvRu+LM0Fr9YVP8RuXic2UKGegO8eoQmNI1i8d8wlsKV1YvbEo4JDrgeQeD FQcFRE7sVB2vVjSUCGmlPPH+1GCZWObs/yNaiAWpAu8J7YfRZZjvf3eu2/5MlayITU p6l5OyYxPHnxw== Message-ID: <19f5f950-d0f9-49c2-acf6-7b0ab277ab23@kernel.org> Date: Thu, 23 Apr 2026 16:27:21 +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 v2] mm/memory: update stale locking comments for fault handlers 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> <20260405171834.15971-1-adi.sharma@zohomail.in> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/5/26 19:18, Aditya Sharma wrote: > Update the comments for wp_page_copy(), do_wp_page(), do_swap_page(), > do_anonymous_page(), __do_fault(), do_fault(), handle_pte_fault(), > __handle_mm_fault(), and handle_mm_fault() to concisely clarify that > they can be entered holding either the mmap_lock or the VMA lock, > and that the lock may be released upon returning VM_FAULT_RETRY. > > Additionally, make the following corrections: > - In do_anonymous_page(), correct the outdated claim that the function > is entered with the PTE "mapped but not yet locked". Since > handle_pte_fault() unmaps the empty PTE before routing to > do_pte_missing(), the comment now correctly states it is entered > with the PTE unmapped and unlocked. > - In __do_fault(), update the stale reference from __lock_page_retry() > to __folio_lock_or_retry(). > > Signed-off-by: Aditya Sharma Next time, please don't send as reply to your previous version > --- > v2: > - Simplified the comment to concisely state "either the VMA lock or > the mmap_lock" instead of a verbose explanation (per David Hildenbrand). > - Expanded the scope to cover 8 other fault handlers in mm/memory.c > that suffered from the same stale mmap_lock comments. > - Fixed an additional historical inaccuracy in do_anonymous_page() > regarding the PTE mapping state on entry. > - Updated a stale reference in __do_fault() from __lock_page_retry() > to __folio_lock_or_retry(). > > > mm/memory.c | 49 ++++++++++++++++++++++++++----------------------- > 1 file changed, 26 insertions(+), 23 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index c65e82c86..2b407e3f9 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -3742,8 +3742,8 @@ vm_fault_t __vmf_anon_prepare(struct vm_fault *vmf) > * Handle the case of a page which we actually need to copy to a new page, > * either due to COW or unsharing. > * > - * Called with mmap_lock locked and the old page referenced, but > - * without the ptl held. > + * Called with either the VMA lock or the mmap_lock (FAULT_FLAG_VMA_LOCK > + * tells you which) "Called with either the VMA lock or the mmap_lock *held*" Same for other cases. Can we shorten "FAULT_FLAG_VMA_LOCK tells you which" to "see FAULT_FLAG_VMA_LOCK" ? -- Cheers, David