From: Zi Yan <[email protected]> migrate_pages() requires at least down_read(mmap_sem) to protect related page tables and VMAs from changing. Let's do it in do_page_moves() for both do_move_pages_to_node() and add_page_for_migration().
Also add this lock requirement in the comment of migrate_pages(). Signed-off-by: Zi Yan <[email protected]> --- mm/migrate.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/mm/migrate.c b/mm/migrate.c index 5d0dc7b85f90..52d029953c32 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1354,6 +1354,9 @@ static int unmap_and_move_huge_page(new_page_t get_new_page, * or free list only if ret != 0. * * Returns the number of pages that were not migrated, or an error code. + * + * The caller must hold at least down_read(mmap_sem) for to-be-migrated pages + * to protect related page tables and VMAs from changing. */ int migrate_pages(struct list_head *from, new_page_t get_new_page, free_page_t put_new_page, unsigned long private, @@ -1457,6 +1460,12 @@ static int store_status(int __user *status, int start, int value, int nr) return 0; } +/* + * Migrates the pages from pagelist and put back those not migrated. + * + * The caller must at least hold down_read(mmap_sem), which is required + * for migrate_pages() + */ static int do_move_pages_to_node(struct mm_struct *mm, struct list_head *pagelist, int node) { @@ -1487,7 +1496,6 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr, unsigned int follflags; int err; - down_read(&mm->mmap_sem); err = -EFAULT; vma = find_vma(mm, addr); if (!vma || addr < vma->vm_start || !vma_migratable(vma)) @@ -1540,7 +1548,6 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr, */ put_page(page); out: - up_read(&mm->mmap_sem); return err; } @@ -1561,6 +1568,7 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes, migrate_prep(); + down_read(&mm->mmap_sem); for (i = start = 0; i < nr_pages; i++) { const void __user *p; unsigned long addr; @@ -1628,6 +1636,7 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes, if (!err) err = err1; out: + up_read(&mm->mmap_sem); return err; } -- 2.15.1
