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-rw-r--r--mm/migrate.c25
1 files changed, 18 insertions, 7 deletions
diff --git a/mm/migrate.c b/mm/migrate.c
index 1ea27b343ccd..93d9a1e25aad 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2031,15 +2031,26 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
/*
- * Clear the old entry under pagetable lock and establish the new PTE.
- * Any parallel GUP will either observe the old page blocking on the
- * page lock, block on the page table lock or observe the new page.
- * The SetPageUptodate on the new page and page_add_new_anon_rmap
- * guarantee the copy is visible before the pagetable update.
+ * Overwrite the old entry under pagetable lock and establish
+ * the new PTE. Any parallel GUP will either observe the old
+ * page blocking on the page lock, block on the page table
+ * lock or observe the new page. The SetPageUptodate on the
+ * new page and page_add_new_anon_rmap guarantee the copy is
+ * visible before the pagetable update.
*/
flush_cache_range(vma, mmun_start, mmun_end);
page_add_anon_rmap(new_page, vma, mmun_start, true);
- pmdp_huge_clear_flush_notify(vma, mmun_start, pmd);
+ /*
+ * At this point the pmd is numa/protnone (i.e. non present) and the TLB
+ * has already been flushed globally. So no TLB can be currently
+ * caching this non present pmd mapping. There's no need to clear the
+ * pmd before doing set_pmd_at(), nor to flush the TLB after
+ * set_pmd_at(). Clearing the pmd here would introduce a race
+ * condition against MADV_DONTNEED, because MADV_DONTNEED only holds the
+ * mmap_sem for reading. If the pmd is set to NULL at any given time,
+ * MADV_DONTNEED won't wait on the pmd lock and it'll skip clearing this
+ * pmd.
+ */
set_pmd_at(mm, mmun_start, pmd, entry);
update_mmu_cache_pmd(vma, address, &entry);
@@ -2053,7 +2064,7 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
* No need to double call mmu_notifier->invalidate_range() callback as
* the above pmdp_huge_clear_flush_notify() did already call it.
*/
- mmu_notifier_invalidate_range_only_end(mm, mmun_start, mmun_end);
+ mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
/* Take an "isolate" reference and put new page on the LRU. */
get_page(new_page);