From: Yang Shi yang.shi@linux.alibaba.com Subject: mm: move_pages: return valid node id in status if the page is already on the target node

Felix Abecassis reports move_pages() would return random status if the pages are already on the target node by the below test program:

---8<---

int main(void) { const long node_id = 1; const long page_size = sysconf(_SC_PAGESIZE); const int64_t num_pages = 8;

unsigned long nodemask = 1 << node_id; long ret = set_mempolicy(MPOL_BIND, &nodemask, sizeof(nodemask)); if (ret < 0) return (EXIT_FAILURE);

void **pages = malloc(sizeof(void*) * num_pages); for (int i = 0; i < num_pages; ++i) { pages[i] = mmap(NULL, page_size, PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_POPULATE | MAP_ANONYMOUS, -1, 0); if (pages[i] == MAP_FAILED) return (EXIT_FAILURE); }

ret = set_mempolicy(MPOL_DEFAULT, NULL, 0); if (ret < 0) return (EXIT_FAILURE);

int *nodes = malloc(sizeof(int) * num_pages); int *status = malloc(sizeof(int) * num_pages); for (int i = 0; i < num_pages; ++i) { nodes[i] = node_id; status[i] = 0xd0; /* simulate garbage values */ }

ret = move_pages(0, num_pages, pages, nodes, status, MPOL_MF_MOVE); printf("move_pages: %ld ", ret); for (int i = 0; i < num_pages; ++i) printf("status[%d] = %d ", i, status[i]); } ---8<---

Then running the program would return nonsense status values: $ ./move_pages_bug move_pages: 0 status[0] = 208 status[1] = 208 status[2] = 208 status[3] = 208 status[4] = 208 status[5] = 208 status[6] = 208 status[7] = 208

This is because the status is not set if the page is already on the target node, but move_pages() should return valid status as long as it succeeds. The valid status may be errno or node id.

We can't simply initialize status array to zero since the pages may be not on node 0. Fix it by updating status with node id which the page is already on.

Link: http://lkml.kernel.org/r/1575584353-125392-1-git-send-email-yang.shi@linux.a... Fixes: a49bd4d71637 ("mm, numa: rework do_pages_move") Signed-off-by: Yang Shi yang.shi@linux.alibaba.com Reported-by: Felix Abecassis fabecassis@nvidia.com Tested-by: Felix Abecassis fabecassis@nvidia.com Suggested-by: Michal Hocko mhocko@suse.com Reviewed-by: John Hubbard jhubbard@nvidia.com Acked-by: Christoph Lameter cl@linux.com Acked-by: Michal Hocko mhocko@suse.com Reviewed-by: Vlastimil Babka vbabka@suse.cz Cc: Mel Gorman mgorman@techsingularity.net Cc: stable@vger.kernel.org [4.17+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/migrate.c | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-)

--- a/mm/migrate.c~mm-move_pages-return-valid-node-id-in-status-if-the-page-is-already-on-the-target-node +++ a/mm/migrate.c @@ -1512,9 +1512,11 @@ static int do_move_pages_to_node(struct /* * Resolves the given address to a struct page, isolates it from the LRU and * puts it to the given pagelist. - * Returns -errno if the page cannot be found/isolated or 0 when it has been - * queued or the page doesn't need to be migrated because it is already on - * the target node + * Returns: + * errno - if the page cannot be found/isolated + * 0 - when it doesn't have to be migrated because it is already on the + * target node + * 1 - when it has been queued */ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr, int node, struct list_head *pagelist, bool migrate_all) @@ -1553,7 +1555,7 @@ static int add_page_for_migration(struct if (PageHuge(page)) { if (PageHead(page)) { isolate_huge_page(page, pagelist); - err = 0; + err = 1; } } else { struct page *head; @@ -1563,7 +1565,7 @@ static int add_page_for_migration(struct if (err) goto out_putpage;

- err = 0; + err = 1; list_add_tail(&head->lru, pagelist); mod_node_page_state(page_pgdat(head), NR_ISOLATED_ANON + page_is_file_cache(head), @@ -1640,8 +1642,17 @@ static int do_pages_move(struct mm_struc */ err = add_page_for_migration(mm, addr, current_node, &pagelist, flags & MPOL_MF_MOVE_ALL); - if (!err) + + if (!err) { + /* The page is already on the target node */ + err = store_status(status, i, current_node, 1); + if (err) + goto out_flush; continue; + } else if (err > 0) { + /* The page is successfully queued for migration */ + continue; + }

err = store_status(status, i, err, 1); if (err) _