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From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
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Subject: Re: +
 mm-migrate-fix-ref-count-handling-when-hugepage_migration_supported-v2.patch
 added to -mm tree
Date: Fri, 26 May 2017 05:41:15 +0000
Message-ID: <20170526054114.GA475@hori1.linux.bs1.fc.nec.co.jp>
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On Thu, May 25, 2017 at 03:46:23PM -0700, akpm@linux-foundation.org wrote:
> 
> The patch titled
>      Subject: mm/migrate: fix refcount handling when !hugepage_migration_supported()
> has been added to the -mm tree.  Its filename is
>      mm-migrate-fix-ref-count-handling-when-hugepage_migration_supported-v2.patch
> 
> This patch should soon appear at
>     http://ozlabs.org/~akpm/mmots/broken-out/mm-migrate-fix-ref-count-handling-when-hugepage_migration_supported-v2.patch
> and later at
>     http://ozlabs.org/~akpm/mmotm/broken-out/mm-migrate-fix-ref-count-handling-when-hugepage_migration_supported-v2.patch
> 
> Before you just go and hit "reply", please:
>    a) Consider who else should be cc'ed
>    b) Prefer to cc a suitable mailing list as well
>    c) Ideally: find the original patch on the mailing list and do a
>       reply-to-all to that, adding suitable additional cc's
> 
> *** Remember to use Documentation/SubmitChecklist when testing your code ***
> 
> The -mm tree is included into linux-next and is updated
> there every 3-4 working days
> 
> ------------------------------------------------------
> From: Punit Agrawal <punit.agrawal@arm.com>
> 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().
> 
> Link: http://lkml.kernel.org/r/20170525135146.32011-1-punit.agrawal@arm.com
> Reported-by: Manoj Iyer <manoj.iyer@canonical.com>
> Tested-by: Manoj Iyer <manoj.iyer@canonical.com>
> Suggested-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Wanpeng Li <wanpeng.li@hotmail.com>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: <stable@vger.kernel.org>	[3.14+]
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  mm/memory-failure.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff -puN mm/memory-failure.c~mm-migrate-fix-ref-count-handling-when-hugepage_migration_supported-v2 mm/memory-failure.c
> --- a/mm/memory-failure.c~mm-migrate-fix-ref-count-handling-when-hugepage_migration_supported-v2
> +++ a/mm/memory-failure.c
> @@ -1600,7 +1600,8 @@ static int soft_offline_huge_page(struct
>  		 * only one hugepage pointed to by hpage, so we need not
>  		 * run through the pagelist here.
>  		 */

Hi Andrew,
I just noticed that the comment above this becomes obsolete with this change,
so could you remove it? (please fold it to this patch.)

@@ -1649,11 +1649,6 @@ static int soft_offline_huge_page(struct page *page, int flags)
 	if (ret) {
 		pr_info("soft offline: %#lx: migration failed %d, type %lx (%pGp)\n",
 			pfn, ret, page->flags, &page->flags);
-		/*
-		 * We know that soft_offline_huge_page() tries to migrate
-		 * only one hugepage pointed to by hpage, so we need not
-		 * run through the pagelist here.
-		 */
 		if (!list_empty(&pagelist))
 			putback_movable_pages(&pagelist);
 		if (ret > 0)

Thanks,
Naoya Horiguchi

> -		putback_active_hugepage(hpage);
> +		if (!list_empty(&pagelist))
> +			putback_movable_pages(&pagelist);
>  		if (ret > 0)
>  			ret = -EIO;
>  	} else {
> _
> 
> Patches currently in -mm which might be from punit.agrawal@arm.com are
> 
> mm-migrate-fix-ref-count-handling-when-hugepage_migration_supported-v2.patch
> mm-gup-ensure-real-head-page-is-ref-counted-when-using-hugepages.patch
> mm-hugetlb-add-size-parameter-to-huge_pte_offset.patch
> mm-hugetlb-allow-architectures-to-override-huge_pte_clear.patch
> mm-hugetlb-introduce-set_huge_swap_pte_at-helper.patch
> mm-hugetlb-introduce-set_huge_swap_pte_at-helper-v4.patch
> mm-hugetlb-introduce-set_huge_swap_pte_at-helper-v41.patch
> mm-rmap-use-correct-helper-when-poisoning-hugepages.patch
> 
>