Patch "mm/migrate: fix refcount handling when !hugepage_migration_supported()" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

mm/migrate: fix refcount handling when !hugepage_migration_supported()

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-migrate-fix-refcount-handling-when-hugepage_migration_supported.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Punit Agrawal <[email protected]>
Date: Fri, 2 Jun 2017 14:46:40 -0700
Subject: mm/migrate: fix refcount handling when !hugepage_migration_supported()

From: Punit Agrawal <[email protected]>

commit 30809f559a0d348c2dfd7ab05e9a451e2384962e upstream.

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.

---
 mm/memory-failure.c |    8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

@@ -1587,12 +1587,8 @@ static int soft_offline_huge_page(struct
 	if (ret) {
 		pr_info("soft offline: %#lx: migration failed %d, type %lx\n",
 			pfn, ret, 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.
-		 */
-		putback_active_hugepage(hpage);
+		if (!list_empty(&pagelist))
+			putback_movable_pages(&pagelist);
 		if (ret > 0)
 			ret = -EIO;
 	} else {

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/mm-migrate-fix-refcount-handling-when-hugepage_migration_supported.patch