Boo, v4 and nobody suggested CCing linux-api yet? Doing that and not trimming the reply, for reference.

On 12/5/19 11:19 PM, Yang Shi wrote:

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\n", ret); for (int i = 0; i < num_pages; ++i) printf("status[%d] = %d\n", 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.

Fixes: a49bd4d71637 ("mm, numa: rework do_pages_move") 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 Cc: Vlastimil Babka vbabka@suse.cz Cc: Mel Gorman mgorman@techsingularity.net Cc: stable@vger.kernel.org 4.17+ Signed-off-by: Yang Shi yang.shi@linux.alibaba.com

Reviewed-by: Vlastimil Babka vbabka@suse.cz

---

v4: * Fixed the comments from Christopher and John and added their Acked-by and Reviewed-by. v3: * Adopted the suggestion from Michal. v2: * Correted the return value when add_page_for_migration() returns 1.

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

diff --git a/mm/migrate.c b/mm/migrate.c index a8f87cb..6b44818f 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1512,9 +1512,11 @@ static int do_move_pages_to_node(struct mm_struct *mm, /*

• 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 mm_struct *mm, unsigned long addr, 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 mm_struct *mm, unsigned long addr, 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_struct *mm, nodemask_t task_nodes, */ 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)