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smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HEBnBRSb; 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="HEBnBRSb" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 184AC1F00A3A; Tue, 4 Aug 2026 07:59:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785830372; bh=XFxakEObTj5ILt5cc6UMrFBA4R2PYJOH6KLglW0VZUA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=HEBnBRSbawyk083vGvvKdEbDf5vihi1OOpO1vAzkk11NCROBU8Ej4mDcVliwr5EjM P8mqXj3BMNHjIvaVuMlGGSenTG3QGlXDdS0uUmhF2PenrH+hDp9aO3zSxyKgAfFKNl VXXKrE4ZvMdnfQ8LFRLK2wNjFP7Jw8W8HhQGgtrTV0jnxJYeFL/rU6tDmUw/9LQ5rT qqRLF7QB0yTx7mtonjlQ3ao0iJfsyTHg3aSDiQAYpEcHN9Tk7SjQ3NBTjf/P8kGiPm 0NjhWfM5vy+45gXYorynlnUdSUsNjXsUZk9oj+7Qc0HSl/ySN+6Sri7KgSNOklq9CM wtc4rhBoRjVLw== Message-ID: <6af71dfd-37b0-4489-8b7a-63478c8fdd4c@kernel.org> Date: Tue, 4 Aug 2026 09:59:26 +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 v3 3/5] mm: Add RCU-based VMA lookup helper that waits for writers Content-Language: en-US To: Suren Baghdasaryan , "Lorenzo Stoakes (ARM)" Cc: akpm@linux-foundation.org, dave.hansen@linux.intel.com, Liam.Howlett@oracle.com, david@redhat.com, willy@infradead.org, shakeel.butt@linux.dev, jannh@google.com, aliceryhl@google.com, arve@android.com, cmllamas@google.com, christian@brauner.io, tkjos@android.com, dsahern@kernel.org, davem@davemloft.net, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org References: <20260802215459.2769283-1-surenb@google.com> <20260802215459.2769283-4-surenb@google.com> <152ee467-b5e4-470c-ad95-c638aa9986bc@kernel.org> <9c301dd5-76cc-40dc-bbab-a79559d6db1a@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 8/3/26 21:13, Suren Baghdasaryan wrote: > On Mon, Aug 3, 2026 at 9:44 AM Lorenzo Stoakes (ARM) wrote: >> Agree this is worth spelling out in the comment (I raised similarly). >> >> Maybe something like: >> >> If a VMA exists which spans @address, return that VMA, read-locked. >> >> If no VMA is mapped there or, very unlikely, a reference count overflow >> occurred, return NULL. >> >> Nothing prevents VMAs being unmapped/mapped before or after the VMA is >> looked up, if a stronger guarantee is required, take an mmap lock. > > This last statement is true only if the function returns NULL, so I > think it should be in the same paragraph as the "If no VMA is > mapped..." sentence and prepended with "In this case...". So: > > If no VMA is mapped there or, very unlikely, a reference count overflow > occurred, return NULL. In this case, nothing prevents VMAs > being unmapped/ > mapped before or after the VMA is looked up, if a stronger guarantee is > required, take an mmap lock. > > Does that sounds good? Yeah, thanks both!