From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: Re: [PATCH] acpi: drop support for force_remove Date: Tue, 11 Apr 2017 15:48:04 +0200 Message-ID: References: <20170403074023.29121-1-mhocko@kernel.org> <20170410171343.GO4618@dhcp22.suse.cz> <3644128.Y1GtXNQdkv@aspire.rjw.lan> <20170411122016.GK6729@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: In-Reply-To: <20170411122016.GK6729@dhcp22.suse.cz> Sender: linux-kernel-owner@vger.kernel.org To: Michal Hocko Cc: "Rafael J. Wysocki" , Joey Lee , Jiri Kosina , Kani Toshimitsu , Len Brown , LKML , ACPI Devel Maling List , linux-api@vger.kernel.org List-Id: linux-api@vger.kernel.org On Tue, Apr 11, 2017 at 2:20 PM, Michal Hocko wrote: > On Tue 11-04-17 00:15:42, Rafael J. Wysocki wrote: >> On Monday, April 10, 2017 07:13:44 PM Michal Hocko wrote: >> > On Mon 03-04-17 09:40:23, Michal Hocko wrote: >> > > From: Michal Hocko >> > > >> > > /sys/firmware/acpi/hotplug/force_remove was presumably added to support >> > > auto offlining in the past. This is, however, inherently dangerous for >> > > some hotplugable resources like memory. The memory offlining fails when >> > > the memory is still in use and cannot be dropped or migrated. If we >> > > ignore the failure we are basically allowing for subtle memory >> > > corruption or a crash. >> > > >> > > We have actually noticed the later while hitting BUG() during the memory >> > > hotremove (remove_memory): >> > > ret = walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1), NULL, >> > > check_memblock_offlined_cb); >> > > if (ret) >> > > BUG(); >> > > >> > > it took us quite non-trivial time realize that the customer had >> > > force_remove enabled. Even if the BUG was removed here and we could >> > > propagate the error up the call chain it wouldn't help at all because >> > > then we would hit a crash or a memory corruption later and harder to >> > > debug. So force_remove is unfixable for the memory hotremove. We haven't >> > > checked other hotplugable resources to be prone to a similar problems. >> > > >> > > Remove the force_remove functionality because it is not fixable currently. >> > > Keep the sysfs file and report an error if somebody tries to enable it. >> > > Encourage users to report about the missing functionality and work with >> > > them with an alternative solution. >> > > >> > > Reviewed-by: Lee, Chun-Yi >> > > Signed-off-by: Michal Hocko >> > >> > ping on this? >> >> /shrug/ >> >> I'll apply it if nobody has any problems with it. > > It is definitely your call but how long are we going to wait > (considering that the current behavior is obviously broken wrt memory > hotplug)? A couple of days more? Surely not going to push it into 4.11 at this stage as it is an ABI change. Thanks, Rafael