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 26B2F2DB785 for ; Fri, 3 Jul 2026 08:20:30 +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=1783066831; cv=none; b=NWgh1qBOAsAJDdQL05I+nNfMo5B4h+SZ2M67Q2ybXZWzm/zVP3GT0J+eUbKNMwj2Wl5bqJVyDzyNqnAEqGqhh9OVbHGTwSx6gl76Qz/btUgHuyUmL4XzSpQAy2mnG8GAzKAM2P18dcrMd7zfq8l39bMI08uSFyzRZ5g3WCYjHWA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783066831; c=relaxed/simple; bh=lEcpHrYEspxXJCxWYVFe+qVrJ2v8yMAAPOjPsV0OEc0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YFO1Mlg4C7zlddJFDE1F1k7Cu+ZR8d4QF+2ykSQJG+AkJ424rNKhSGZHG1dGziS9SUTqkXudWszQurLJhrlyIeLfjc2yYRiI26MIyi2XRweNNpZFUMgXTsv8QV+ukNa4rY+AAZwMUEW+2G+IjMyBdCCFapAyzJTxEQlr6NF8MCs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CaOXshCG; 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="CaOXshCG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 41CF21F000E9; Fri, 3 Jul 2026 08:20:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783066830; bh=9eBMQkRAIIiiD1/VSxT9ESyU/aInOBlcadzqDqKcKNU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=CaOXshCG6r0+KBtTiJ19wWhAxgPjDZye71u/BG7CxHsUKpc3RHiFsgmNAeoXaP1O4 6q32HMx8WwAwDQ58RRTmrRifC4mAW8dC4TvarNI8+sQgmwe920m/4AzlBEtLpLhUnv PexAmaNntL2iK8cp5YJfzouP7DSHBijvWa3ildUzneJR3Akh0lLJxwVo5vA3YfUcxN eqFZDhZZ8F1IXrGYXkgBr/Q7TTeAe7qvd3SniX7e3uYRD5TCXV2NKzTxCjRDvZ9KDv 3Ac37l+nwyONhEBaK8V/CMqJYHGG2LwHPtl7RtRBk53oEbRAFDhwbs7QlbV0LO8k4Z TPLu6FVOoI9kw== Message-ID: <2436707a-b6ab-45ec-98e5-538e18589462@kernel.org> Date: Fri, 3 Jul 2026 10:20:25 +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 RFC hotfixes 2/2] mm/slab: prevent unbounded recursion in free path with new kmalloc type Content-Language: en-US To: Harry Yoo , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Suren Baghdasaryan , Hao Ge , Kees Cook , Pedro Falcato , Shakeel Butt , Danielle Constantino Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260702-kmalloc-no-objext-v1-0-167175008538@kernel.org> <20260702-kmalloc-no-objext-v1-2-167175008538@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/2/26 15:20, Harry Yoo wrote: > > > On 7/2/26 9:57 PM, Vlastimil Babka (SUSE) wrote: >>> >>> To achieve this, create a new kmalloc type called KMALLOC_NO_OBJ_EXT. >>> KMALLOC_NO_OBJ_EXT caches are created when CONFIG_SLAB_OBJ_EXT is >>> enabled, and they have SLAB_NO_OBJ_EXT flag to prevent allocation >>> of obj_exts arrays. They remain unused until allocation of obj_exts >>> arrays for normal kmalloc caches happens. >> >> I wonder if we should just use them always (not just for kmalloc_normal) if >> we already have them. Would there be any downside? > > Good point! > > That's more intuitive and sounds like it's good to separate them because > likely obj_exts will have longer lifetime than slab objects. > > Not sure about impact on memory usage, need to check. > I'd say it's fine as long as it doesn't clearly increase memory usage. Yeah there might be more usage due to separate slabs, sheaves etc. But maybe also less because the separated lifetime, thus potentially lower internal fragmentation. > But I guess that should not be part of bugfix as it's a functional > change that is not required to fix the bug. Ack.