Skip to contentSkip to conversation

FAILED: patch "[PATCH] mm/thp: fix __split_huge_pmd_locked() for migration PMD" failed to apply to 4.19-stable tree

PATCH [email protected] 1 participant 1 message Sep 21, 2020

Subsystems (3)
Stable branch Memory management THP
lore
Share & tools
lore

[email protected]

author maintainer
#0 lore raw

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From ec0abae6dcdf7ef88607c869bf35a4b63ce1b370 Mon Sep 17 00:00:00 2001
From: Ralph Campbell <[email protected]>
Date: Fri, 18 Sep 2020 21:20:24 -0700
Subject: [PATCH] mm/thp: fix __split_huge_pmd_locked() for migration PMD

A migrating transparent huge page has to already be unmapped. Otherwise, the page could be modified while it is being copied to a new page and data could be lost. The function __split_huge_pmd() checks for a PMD migration entry before calling __split_huge_pmd_locked() leading one to think that __split_huge_pmd_locked() can handle splitting a migrating PMD.

However, the code always increments the page->_mapcount and adjusts the memory control group accounting assuming the page is mapped.

Also, if the PMD entry is a migration PMD entry, the call to is_huge_zero_pmd(*pmd) is incorrect because it calls pmd_pfn(pmd) instead of migration_entry_to_pfn(pmd_to_swp_entry(pmd)). Fix these problems by checking for a PMD migration entry.

Fixes 84c3fc4e9c56 ("mm: thp: check pmd migration entry in common path")
Signed-off-by Ralph Campbell <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
Reviewed-by Yang Shi <[email protected]>
Reviewed-by Zi Yan <[email protected]>
Cc Jerome Glisse <[email protected]>
Cc John Hubbard <[email protected]>
Cc Alistair Popple <[email protected]>
Cc Christoph Hellwig <[email protected]>
Cc Jason Gunthorpe <[email protected]>
Cc Bharata B Rao <[email protected]>
Cc Ben Skeggs <[email protected]>
Cc Shuah Khan <[email protected]>
Cc <[email protected]> [4.14+]
Link https://lkml.kernel.org/r/[email protected] open here
Signed-off-by Linus Torvalds <[email protected]>
mm/huge_memory.c +23 -19
index 7ff29cc3d55c..faadc449cca5 100644
@@ -2022,7 +2022,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 		put_page(page);
 		add_mm_counter(mm, mm_counter_file(page), -HPAGE_PMD_NR);
 		return;
-	} else if (is_huge_zero_pmd(*pmd)) {
+	} else if (pmd_trans_huge(*pmd) && is_huge_zero_pmd(*pmd)) {
 		/*
 		 * FIXME: Do we want to invalidate secondary mmu by calling
 		 * mmu_notifier_invalidate_range() see comments below inside

@@ -2116,30 +2116,34 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 		pte = pte_offset_map(&_pmd, addr);
 		BUG_ON(!pte_none(*pte));
 		set_pte_at(mm, addr, pte, entry);
-		atomic_inc(&page[i]._mapcount);
-		pte_unmap(pte);
-	}
-
-	/*
-	 * Set PG_double_map before dropping compound_mapcount to avoid
-	 * false-negative page_mapped().
-	 */
-	if (compound_mapcount(page) > 1 && !TestSetPageDoubleMap(page)) {
-		for (i = 0; i < HPAGE_PMD_NR; i++)
+		if (!pmd_migration)
 			atomic_inc(&page[i]._mapcount);
+		pte_unmap(pte);
 	}
 
-	lock_page_memcg(page);
-	if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
-		/* Last compound_mapcount is gone. */
-		__dec_lruvec_page_state(page, NR_ANON_THPS);
-		if (TestClearPageDoubleMap(page)) {
-			/* No need in mapcount reference anymore */
+	if (!pmd_migration) {
+		/*
+		 * Set PG_double_map before dropping compound_mapcount to avoid
+		 * false-negative page_mapped().
+		 */
+		if (compound_mapcount(page) > 1 &&
+		    !TestSetPageDoubleMap(page)) {
 			for (i = 0; i < HPAGE_PMD_NR; i++)
-				atomic_dec(&page[i]._mapcount);
+				atomic_inc(&page[i]._mapcount);
+		}
+
+		lock_page_memcg(page);
+		if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
+			/* Last compound_mapcount is gone. */
+			__dec_lruvec_page_state(page, NR_ANON_THPS);
+			if (TestClearPageDoubleMap(page)) {
+				/* No need in mapcount reference anymore */
+				for (i = 0; i < HPAGE_PMD_NR; i++)
+					atomic_dec(&page[i]._mapcount);
+			}
 		}
+		unlock_page_memcg(page);
 	}
-	unlock_page_memcg(page);
 
 	smp_wmb(); /* make pte visible before pmd */
 	pmd_populate(mm, pmd, pgtable);