Commit faf53def authored Jun 28, 2019 by Naoya Horiguchi Committed by Linus Torvalds Jun 29, 2019

mm: hugetlb: soft-offline: dissolve_free_huge_page() return zero on !PageHuge

madvise(MADV_SOFT_OFFLINE) often returns -EBUSY when calling soft offline
for hugepages with overcommitting enabled.  That was caused by the
suboptimal code in current soft-offline code.  See the following part:

    ret = migrate_pages(&pagelist, new_page, NULL, MPOL_MF_MOVE_ALL,
                            MIGRATE_SYNC, MR_MEMORY_FAILURE);
    if (ret) {
            ...
    } else {
            /*
             * We set PG_hwpoison only when the migration source hugepage
             * was successfully dissolved, because otherwise hwpoisoned
             * hugepage remains on free hugepage list, then userspace will
             * find it as SIGBUS by allocation failure. That's not expected
             * in soft-offlining.
             */
            ret = dissolve_free_huge_page(page);
            if (!ret) {
                    if (set_hwpoison_free_buddy_page(page))
                            num_poisoned_pages_inc();
            }
    }
    return ret;

Here dissolve_free_huge_page() returns -EBUSY if the migration source page
was freed into buddy in migrate_pages(), but even in that case we actually
has a chance that set_hwpoison_free_buddy_page() succeeds.  So that means
current code gives up offlining too early now.

dissolve_free_huge_page() checks that a given hugepage is suitable for
dissolving, where we should return success for !PageHuge() case because
the given hugepage is considered as already dissolved.

This change also affects other callers of dissolve_free_huge_page(), which
are cleaned up together.

[n-horiguchi@ah.jp.nec.com: v3]
  Link: http://lkml.kernel.org/r/1560761476-4651-3-git-send-email-n-horiguchi@ah.jp.nec.comLink: http://lkml.kernel.org/r/1560154686-18497-3-git-send-email-n-horiguchi@ah.jp.nec.com


Fixes: 6bc9b564 ("mm: fix race on soft-offlining")
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reported-by: Chen, Jerry T <jerry.t.chen@intel.com>
Tested-by: Chen, Jerry T <jerry.t.chen@intel.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Xishi Qiu <xishi.qiuxishi@alibaba-inc.com>
Cc: "Chen, Jerry T" <jerry.t.chen@intel.com>
Cc: "Zhuo, Qiuxu" <qiuxu.zhuo@intel.com>
Cc: <stable@vger.kernel.org>	[4.19+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent b38e5962

mm/hugetlb.c

+20 −9

Original line number	Diff line number	Diff line
		@@ -1510,16 +1510,29 @@ static int free_pool_huge_page(struct hstate h, nodemask_t nodes_allowed,

		/*
		* Dissolve a given free hugepage into free buddy pages. This function does
		* nothing for in-use (including surplus) hugepages. Returns -EBUSY if the
		* dissolution fails because a give page is not a free hugepage, or because
		* free hugepages are fully reserved.
		* nothing for in-use hugepages and non-hugepages.
		* This function returns values like below:
		*
		* -EBUSY: failed to dissolved free hugepages or the hugepage is in-use
		* (allocated or reserved.)
		* 0: successfully dissolved free hugepages or the page is not a
		* hugepage (considered as already dissolved)
		*/
		int dissolve_free_huge_page(struct page *page)
		{
		int rc = -EBUSY;

		/* Not to disrupt normal path by vainly holding hugetlb_lock */
		if (!PageHuge(page))
		return 0;

		spin_lock(&hugetlb_lock);
		if (PageHuge(page) && !page_count(page)) {
		if (!PageHuge(page)) {
		rc = 0;
		goto out;
		}

		if (!page_count(page)) {
		struct page *head = compound_head(page);
		struct hstate *h = page_hstate(head);
		int nid = page_to_nid(head);
		@@ -1564,12 +1577,10 @@ int dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)

		for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << minimum_order) {
		page = pfn_to_page(pfn);
		if (PageHuge(page) && !page_count(page)) {
		rc = dissolve_free_huge_page(page);
		if (rc)
		break;
		}
		}

		return rc;
		}

mm/memory-failure.c

+1 −4

Original line number	Diff line number	Diff line
		@@ -1856,11 +1856,8 @@ static int soft_offline_in_use_page(struct page *page, int flags)

		static int soft_offline_free_page(struct page *page)
		{
		int rc = 0;
		struct page *head = compound_head(page);
		int rc = dissolve_free_huge_page(page);

		if (PageHuge(head))
		rc = dissolve_free_huge_page(page);
		if (!rc) {
		if (set_hwpoison_free_buddy_page(page))
		num_poisoned_pages_inc();

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