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 6EDEB3815ED; Thu, 25 Jun 2026 07:40:11 +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=1782373213; cv=none; b=tsVTWkbyzYubbvTxujdbm5JYkFlaa8IXdq0Juz3rhCK3ZK8ieHczjwm5lnRp/ccFMy6sRcFY+yep3E63AX5DfmNcdF9PSa6BgliePE98zSM0H8yznEF3EhaBnaZ3ZG24+GiHBHKJIyAAuBu8dm0q8rCcEjr5VzwjjFZy9IjMHKs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782373213; c=relaxed/simple; bh=wLp3MaGuBaurQfyTF7tq7PviXwXQ+F8xCjPM7/OW12s=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=nazyw8nMIVeYlRG2dPAM26TAxPt0TDTAWjKeEI8ZbzplwD8ObGj0DpdikYPDgGmIuf24aV3npMr/+u4YLigPe3qZHg7WLTD3nKvez0ndXqOQZ9iXebeaYEbD1xRqabZPAiiVLDcVdiWjXPgSDvZWrBo/bZG1icLvq2gwvbFATsA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SNY0gmJI; 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="SNY0gmJI" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6E00A1F00A3A; Thu, 25 Jun 2026 07:40:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782373211; bh=D0yxXYlC+6ZzOInCXh8esiMObDCmFa28JgIqXqu60pE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=SNY0gmJIRd8aAsNgBLSo9uATdut1LoqElrTqsbgNwRX34c4pz0dA2LXltTCm5J2jd GCKHbC/0HGMiLrrlgZ7sJgoYk/hvOlx2FQsSzSGbHdvEvi2Y6fHGEOv+6errkLxuyN FEG4hWpDHHl+2/TbXpxcGR+W7rPBRxmUm7UluzvbnL7Pv9Fc+0i8btgnVJEZnCPSTT oXx/29zepKkQnx7lLBxYJuk4hVstAm3j549aahwWIoI7j+zXF7pE6/py3rP9S4IaX/ hYNwq2jhob3kh6PbUWCnnIc6d0oNUzlfu7kXxyZ4x5BAf9EGrZ6nJLQ+SU/c15xN9o IVgh763KB88WQ== Message-ID: <1d8f74a7-502b-43cb-a0f0-1923049aa213@kernel.org> Date: Thu, 25 Jun 2026 09:40:02 +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 v5 8/9] dax/kmem: add sysfs interface for atomic whole-device hotplug To: Gregory Price , linux-mm@kvack.org, nvdimm@lists.linux.dev Cc: linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org, driver-core@lists.linux.dev, linux-kselftest@vger.kernel.org, kernel-team@meta.com, osalvador@suse.de, gregkh@linuxfoundation.org, rafael@kernel.org, dakr@kernel.org, djbw@kernel.org, vishal.l.verma@intel.com, dave.jiang@intel.com, akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, shuah@kernel.org, alison.schofield@intel.com, Smita.KoralahalliChannabasappa@amd.com, ira.weiny@intel.com, apopple@nvidia.com, Hannes Reinecke References: <20260624145744.3532049-1-gourry@gourry.net> <20260624145744.3532049-9-gourry@gourry.net> 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 6/24/26 16:57, Gregory Price wrote: > There is no atomic mechanism to offline and remove an entire > multi-block DAX kmem device. This is presently done in two steps: > 1. offline all > 2. remove all). > > This creates a race condition where another entity operates directly > on the memory blocks and can cause hot-unplug to fail / unbind to > deadlock. > > Add a new 'state' sysfs attribute that enables an atomic whole-device > hotplug operation across its entire memory region. > > daxX.Y/state mirrors the per-block memoryX/state ABI: > - [offline, online, online_kernel, online_movable] > - "unplugged" - is added specifically for dax0.0/state > > The valid writable states include: > - "unplugged": memory blocks are not present > - "online": memory is online, zone chosen by the kernel > - "online_kernel": memory is online in ZONE_NORMAL > - "online_movable": memory is online in ZONE_MOVABLE > > Valid transitions: > - unplugged -> online[_kernel|_movable] > - online[_kernel|_movable] -> unplugged > - offline -> unplugged > > A device can only be onlined from "unplugged", so it must be returned > there before being onlined into a different state. > > For backwards compatibility the memory blocks are always created at > probe - existing tools expect them to be present after kmem binds. > > "offline" is therefore a reportable state but is not writable: it only > arises from the legacy auto_online_blocks=offline policy. Onlining > such a device through this attribute requires unplugging it first in > an effort to get drivers creating DAX devices to set a default. > > Unplug is atomic across the whole device: dax_kmem_do_hotremove() > collects every added range and offlines/removes them in one operation. > Either the operation succeeds or is entirely rolled back. > > Unbind Note: > We used to call remove_memory() during unbind, which would fire a > BUG() if any of the memory blocks were online at that time. We lift > this into a WARN in the cleanup routine and don't attempt hotremove > if ->state is not DAX_KMEM_UNPLUGGED or MMOP_OFFLINE. > > An offline dax device memory is removed on unbind as before. > > If online at unbind, the resources are leaked (as before), but now > we prevent deadlock if a memory region is impossible to hotremove. > > Suggested-by: Hannes Reinecke > Suggested-by: David Hildenbrand > Signed-off-by: Gregory Price > --- > Documentation/ABI/testing/sysfs-bus-dax | 26 +++ > drivers/base/memory.c | 9 + Can we have this ... > drivers/dax/kmem.c | 224 ++++++++++++++++++++---- > include/linux/memory_hotplug.h | 1 + > ... and this as a separate patch, please? Nothing else jumped at me. -- Cheers, David