On Thu, May 25, 2017 at 03:46:23PM -0700, akpm@xxxxxxxxxxxxxxxxxxxx wrote: > ------------------------------------------------------ > From: Punit Agrawal <punit.agrawal@xxxxxxx> > Subject: mm/migrate: fix refcount handling when !hugepage_migration_supported() > > On failing to migrate a page, soft_offline_huge_page() performs the > necessary update to the hugepage ref-count. When > !hugepage_migration_supported() , unmap_and_move_hugepage() also > decrements the page ref-count for the hugepage. The combined behaviour > leaves the ref-count in an inconsistent state. > > This leads to soft lockups when running the overcommitted hugepage test > from mce-tests suite. > > Soft offlining pfn 0x83ed600 at process virtual address 0x400000000000 > soft offline: 0x83ed600: migration failed 1, type > 1fffc00000008008 (uptodate|head) > INFO: rcu_preempt detected stalls on CPUs/tasks: > Tasks blocked on level-0 rcu_node (CPUs 0-7): P2715 > (detected by 7, t=5254 jiffies, g=963, c=962, q=321) > thugetlb_overco R running task 0 2715 2685 0x00000008 > Call trace: > [<ffff000008089f90>] dump_backtrace+0x0/0x268 > [<ffff00000808a2d4>] show_stack+0x24/0x30 > [<ffff000008100d34>] sched_show_task+0x134/0x180 > [<ffff0000081c90fc>] rcu_print_detail_task_stall_rnp+0x54/0x7c > [<ffff00000813cfd4>] rcu_check_callbacks+0xa74/0xb08 > [<ffff000008143a3c>] update_process_times+0x34/0x60 > [<ffff0000081550e8>] tick_sched_handle.isra.7+0x38/0x70 > [<ffff00000815516c>] tick_sched_timer+0x4c/0x98 > [<ffff0000081442e0>] __hrtimer_run_queues+0xc0/0x300 > [<ffff000008144fa4>] hrtimer_interrupt+0xac/0x228 > [<ffff0000089a56d4>] arch_timer_handler_phys+0x3c/0x50 > [<ffff00000812f1bc>] handle_percpu_devid_irq+0x8c/0x290 > [<ffff0000081297fc>] generic_handle_irq+0x34/0x50 > [<ffff000008129f00>] __handle_domain_irq+0x68/0xc0 > [<ffff0000080816b4>] gic_handle_irq+0x5c/0xb0 > > Address this by changing the putback_active_hugepage() in > soft_offline_huge_page() to putback_movable_pages(). > I've never looked too closely at how hardware poisoning and hugetlb pages migration is handled so I could easily have missed something but this changelog and patch confuses me. Surely if the inconsistency is between hugepage_migration_supported and !hugepage_migration_supported then the check in soft_offline_huge_page() should also be related to hugepage_migration_supported either in soft_offline_huge_page() or in putback_movable_pages()? -- Mel Gorman SUSE Labs