[PATCHv3 18/24] thp, mm: split_huge_page(): caller need to lock page

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

We're going to use migration entries instead of compound_lock() to
stabilize page refcounts. Setup and remove migration entries require
page to be locked.

Some of split_huge_page() callers already have the page locked. Let's
require everybody to lock the page before calling split_huge_page().

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 mm/huge_memory.c    |  1 +
 mm/ksm.c            |  6 ++++--
 mm/memory-failure.c | 12 +++++++++---
 mm/migrate.c        |  8 ++++++--
 4 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index fa79d3b89825..bb9be39de242 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1841,6 +1841,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 
 	BUG_ON(is_huge_zero_page(page));
 	BUG_ON(!PageAnon(page));
+	BUG_ON(!PageLocked(page));
 
 	/*
 	 * The caller does not necessarily hold an mmap_sem that would prevent
diff --git a/mm/ksm.c b/mm/ksm.c
index 92182eeba87d..a8a88b0f6f62 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -987,9 +987,11 @@ static int page_trans_compound_anon_split(struct page *page)
 			 * Recheck we got the reference while the head
 			 * was still anonymous.
 			 */
-			if (PageAnon(transhuge_head))
+			if (PageAnon(transhuge_head)) {
+				lock_page(transhuge_head);
 				ret = split_huge_page(transhuge_head);
-			else
+				unlock_page(transhuge_head);
+			} else
 				/*
 				 * Retry later if split_huge_page run
 				 * from under us.
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 1a735fad2a13..006a891c9222 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -950,7 +950,10 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
 		 * enough * to be safe.
 		 */
 		if (!PageHuge(hpage) && PageAnon(hpage)) {
-			if (unlikely(split_huge_page(hpage))) {
+			lock_page(hpage);
+			ret = split_huge_page(hpage);
+			unlock_page(hpage);
+			if (unlikely(ret)) {
 				/*
 				 * FIXME: if splitting THP is failed, it is
 				 * better to stop the following operation rather
@@ -1696,10 +1699,13 @@ int soft_offline_page(struct page *page, int flags)
 		return -EBUSY;
 	}
 	if (!PageHuge(page) && PageTransHuge(hpage)) {
-		if (PageAnon(hpage) && unlikely(split_huge_page(hpage))) {
+		lock_page(page);
+		ret = split_huge_page(hpage);
+		unlock_page(page);
+		if (unlikely(ret)) {
 			pr_info("soft offline: %#lx: failed to split THP\n",
 				pfn);
-			return -EBUSY;
+			return ret;
 		}
 	}
 
diff --git a/mm/migrate.c b/mm/migrate.c
index 01449826b914..91a67029bb18 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -920,9 +920,13 @@ static int unmap_and_move(new_page_t get_new_page, free_page_t put_new_page,
 		goto out;
 	}
 
-	if (unlikely(PageTransHuge(page)))
-		if (unlikely(split_huge_page(page)))
+	if (unlikely(PageTransHuge(page))) {
+		lock_page(page);
+		rc = split_huge_page(page);
+		unlock_page(page);
+		if (rc)
 			goto out;
+	}
 
 	rc = __unmap_and_move(page, newpage, force, mode);
 
-- 
2.1.4

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