On Tue, Apr 11, 2017 at 2:20 PM, Michal Hocko <mhocko@xxxxxxxxxx> 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 <mhocko@xxxxxxxx> >> > > >> > > /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 <jlee@xxxxxxxx> >> > > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> >> > >> > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
