ACK: [PATCH] mm/migrate: fix refcount handling when !hugepage_migration_supported()

[Seth Forshee]

On Mon, Jun 19, 2017 at 12:20:14PM -0500, Manoj Iyer wrote:
> From: Punit Agrawal <punit.agrawal at arm.com>
> 
> On failing to migrate a page, soft_offline_huge_page() performs the
> necessary update to the hugepage ref-count.
> 
> But 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:
>       dump_backtrace+0x0/0x268
>       show_stack+0x24/0x30
>       sched_show_task+0x134/0x180
>       rcu_print_detail_task_stall_rnp+0x54/0x7c
>       rcu_check_callbacks+0xa74/0xb08
>       update_process_times+0x34/0x60
>       tick_sched_handle.isra.7+0x38/0x70
>       tick_sched_timer+0x4c/0x98
>       __hrtimer_run_queues+0xc0/0x300
>       hrtimer_interrupt+0xac/0x228
>       arch_timer_handler_phys+0x3c/0x50
>       handle_percpu_devid_irq+0x8c/0x290
>       generic_handle_irq+0x34/0x50
>       __handle_domain_irq+0x68/0xc0
>       gic_handle_irq+0x5c/0xb0
> 
> Address this by changing the putback_active_hugepage() in
> soft_offline_huge_page() to putback_movable_pages().
> 
> This only triggers on systems that enable memory failure handling
> (ARCH_SUPPORTS_MEMORY_FAILURE) but not hugepage migration
> (!ARCH_ENABLE_HUGEPAGE_MIGRATION).
> 
> I imagine this wasn't triggered as there aren't many systems running
> this configuration.
> 
> BugLink: https://launchpad.net/bugs/1696165
> 
> [akpm at linux-foundation.org: remove dead comment, per Naoya]
> Link: http://lkml.kernel.org/r/20170525135146.32011-1-punit.agrawal@arm.com
> Reported-by: Manoj Iyer <manoj.iyer at canonical.com>
> Tested-by: Manoj Iyer <manoj.iyer at canonical.com>
> Suggested-by: Naoya Horiguchi <n-horiguchi at ah.jp.nec.com>
> Signed-off-by: Punit Agrawal <punit.agrawal at arm.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim at lge.com>
> Cc: Wanpeng Li <wanpeng.li at hotmail.com>
> Cc: Christoph Lameter <cl at linux.com>
> Cc: Mel Gorman <mgorman at techsingularity.net>
> Cc: <stable at vger.kernel.org>	[3.14+]
> Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> 
> (backported from commit 30809f559a0d348c2dfd7ab05e9a451e2384962e)
> Signed-off-by: Manoj Iyer <manoj.iyer at canonical.com>

Acked-by: Seth Forshee <seth.forshee at canonical.com>