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Subject[PATCHv4 18/24] thp, mm: split_huge_page(): caller need to lock page
Date
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 3741f81e423e..f1d88b9059e2 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1846,6 +1846,7 @@ 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 d487f8dc6d39..74c5aaddae85 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
@@ -1694,10 +1697,13 @@ 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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