On Tue, 4 Jul 2017, Vlastimil Babka wrote: > On 07/04/2017 11:32 AM, Thomas Gleixner wrote: > > Andrey reported a potential deadlock with the memory hotplug lock and the > > cpu hotplug lock. > > > > The reason is that memory hotplug takes the memory hotplug lock and then > > calls stop_machine() which calls get_online_cpus(). That's the reverse lock > > order to get_online_cpus(); get_online_mems(); in mm/slub_common.c > > > > The problem has been there forever. The reason why this was never reported > > is that the cpu hotplug locking had this homebrewn recursive reader writer > > semaphore construct which due to the recursion evaded the full lock dep > > coverage. The memory hotplug code copied that construct verbatim and > > therefor has similar issues. > > > > Three steps to fix this: > > > > 1) Convert the memory hotplug locking to a per cpu rwsem so the potential > > issues get reported proper by lockdep. > > > > 2) Lock the online cpus in mem_hotplug_begin() before taking the memory > > hotplug rwsem and use stop_machine_cpuslocked() in the page_alloc code > > and use to avoid recursive locking. > > ^ s/and use // ? Ooops, yes. Thanks, tglx -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
