+ mmhwpoison-try-to-narrow-window-race-for-free-pages.patch added to -mm tree

+ mmhwpoison-try-to-narrow-window-race-for-free-pages.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm,hwpoison: try to narrow window race for free pages
has been added to the -mm tree.  Its filename is
     mmhwpoison-try-to-narrow-window-race-for-free-pages.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mmhwpoison-try-to-narrow-window-race-for-free-pages.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mmhwpoison-try-to-narrow-window-race-for-free-pages.patch

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------------------------------------------------------
From: Oscar Salvador <osalvador@suse.de>
Subject: mm,hwpoison: try to narrow window race for free pages

Aristeu Rozanski reported that a customer test case started to report
-EBUSY after the hwpoison rework patchset.

There is a race window between spotting a free page and taking it off its
buddy freelist, so it might be that by the time we try to take it off, the
page has been already allocated.

This patch tries to handle such race window by trying to handle the new
type of page again if the page was allocated under us.

Link: https://lkml.kernel.org/r/20200922135650.1634-15-osalvador@suse.de
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Reported-by: Aristeu Rozanski <aris@ruivo.org>
Tested-by: Aristeu Rozanski <aris@ruivo.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dmitry Yakunin <zeil@yandex-team.ru>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Oscar Salvador <osalvador@suse.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memory-failure.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/mm/memory-failure.c~mmhwpoison-try-to-narrow-window-race-for-free-pages
+++ a/mm/memory-failure.c
@@ -1903,6 +1903,7 @@ int soft_offline_page(unsigned long pfn,
 {
 	int ret;
 	struct page *page;
+	bool try_again = true;
 
 	if (!pfn_valid(pfn))
 		return -ENXIO;
@@ -1918,6 +1919,7 @@ int soft_offline_page(unsigned long pfn,
 		return 0;
 	}
 
+retry:
 	get_online_mems();
 	ret = get_any_page(page, pfn, flags);
 	put_online_mems();
@@ -1925,7 +1927,10 @@ int soft_offline_page(unsigned long pfn,
 	if (ret > 0)
 		ret = soft_offline_in_use_page(page);
 	else if (ret == 0)
-		ret = soft_offline_free_page(page);
+		if (soft_offline_free_page(page) && try_again) {
+			try_again = false;
+			goto retry;
+		}
 
 	return ret;
 }
_

Patches currently in -mm which might be from osalvador@suse.de are

mmhwpoison-unexport-get_hwpoison_page-and-make-it-static.patch
mmhwpoison-refactor-madvise_inject_error.patch
mmhwpoison-kill-put_hwpoison_page.patch
mmhwpoison-unify-thp-handling-for-hard-and-soft-offline.patch
mmhwpoison-rework-soft-offline-for-free-pages.patch
mmhwpoison-rework-soft-offline-for-in-use-pages.patch
mmhwpoison-refactor-soft_offline_huge_page-and-__soft_offline_page.patch
mmhwpoison-return-0-if-the-page-is-already-poisoned-in-soft-offline.patch
mmhwpoison-try-to-narrow-window-race-for-free-pages.patch
mmhwpoison-take-free-pages-off-the-buddy-freelists.patch
mmhwpoison-drain-pcplists-before-bailing-out-for-non-buddy-zero-refcount-page.patch
mmhwpoison-drop-unneeded-pcplist-draining.patch
mmhwpoison-remove-stale-code.patch