mm/memfd: use folio_nr_pages() for shmem inode accounting

I found several modifiable points while reading the code.

This patch (of 6):

Patch series "Modify memfd_luo code", v3.

memfd_luo_retrieve_folios() called shmem_inode_acct_blocks() and
shmem_recalc_inode() with hardcoded 1 instead of the actual folio page
count.  memfd may use large folios (THP/hugepages), causing quota/limit
under-accounting and incorrect stat output.

Fix by using folio_nr_pages(folio) for both functions.

Issue found by AI review and suggested by Pratyush Yadav <pratyush@kernel.org>.
https://sashiko.dev/#/patchset/20260319012845.29570-1-duanchenghao%40kylinos.cn

Link: https://lore.kernel.org/20260326084727.118437-1-duanchenghao@kylinos.cn
Link: https://lore.kernel.org/20260326084727.118437-2-duanchenghao@kylinos.cn
Signed-off-by: Chenghao Duan <duanchenghao@kylinos.cn>
Suggested-by: Pratyush Yadav <pratyush@kernel.org>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Haoran Jiang <jianghaoran@kylinos.cn>
Cc: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c
index 9130e6ce396d8f65b5ee0f2a971256b2974fc545..ec4c3e1e2891cc5b46b7b5830c3319ff0bbd781a 100644 (file)
--- a/mm/memfd_luo.c
+++ b/mm/memfd_luo.c
@@ -410,6 +410,7 @@ static int memfd_luo_retrieve_folios(struct file *file,
        struct inode *inode = file_inode(file);
        struct address_space *mapping = inode->i_mapping;
        struct folio *folio;
+       long npages;
        int err = -EIO;
        long i;
 
@@ -456,14 +457,15 @@ static int memfd_luo_retrieve_folios(struct file *file,
                if (flags & MEMFD_LUO_FOLIO_DIRTY)
                        folio_mark_dirty(folio);
 
-               err = shmem_inode_acct_blocks(inode, 1);
+               npages = folio_nr_pages(folio);
+               err = shmem_inode_acct_blocks(inode, npages);
                if (err) {
-                       pr_err("shmem: failed to account folio index %ld: %d\n",
-                              i, err);
+                       pr_err("shmem: failed to account folio index %ld(%ld pages): %d\n",
+                              i, npages, err);
                        goto unlock_folio;
                }
 
-               shmem_recalc_inode(inode, 1, 0);
+               shmem_recalc_inode(inode, npages, 0);
                folio_add_lru(folio);
                folio_unlock(folio);
                folio_put(folio);