Four folio-related fixes for 5.19:

- Don't release a folio while it's still locked
 
  - Fix a use-after-free after dropping the mmap_lock
 
  - Fix a memory leak when splitting a page
 
  - Fix a kernel-doc warning for struct folio
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Merge tag 'folio-5.19a' of git://git.infradead.org/users/willy/pagecache

Pull folio fixes from Matthew Wilcox:
 "Four folio-related fixes:

   - Don't release a folio while it's still locked

   - Fix a use-after-free after dropping the mmap_lock

   - Fix a memory leak when splitting a page

   - Fix a kernel-doc warning for struct folio"

* tag 'folio-5.19a' of git://git.infradead.org/users/willy/pagecache:
  mm: Add kernel-doc for folio->mlock_count
  mm/huge_memory: Fix xarray node memory leak
  filemap: Cache the value of vm_flags
  filemap: Don't release a locked folio

include/linux/mm_types.h

@@ -227,6 +227,7 @@ struct page {
  * struct folio - Represents a contiguous set of bytes.
  * @flags: Identical to the page flags.
  * @lru: Least Recently Used list; tracks how recently this folio was used.
+ * @mlock_count: Number of times this folio has been pinned by mlock().
  * @mapping: The file this page belongs to, or refers to the anon_vma for
  *    anonymous memory.
  * @index: Offset within the file, in units of pages.  For anonymous memory,
@@ -255,10 +256,14 @@ struct folio {
 			unsigned long flags;
 			union {
 				struct list_head lru;
+	/* private: avoid cluttering the output */
 				struct {
 					void *__filler;
+	/* public: */
 					unsigned int mlock_count;
+	/* private: */
 				};
+	/* public: */
 			};
 			struct address_space *mapping;
 			pgoff_t index;

include/linux/xarray.h

@@ -1508,6 +1508,7 @@ void *xas_find_marked(struct xa_state *, unsigned long max, xa_mark_t);
 void xas_init_marks(const struct xa_state *);
 
 bool xas_nomem(struct xa_state *, gfp_t);
+void xas_destroy(struct xa_state *);
 void xas_pause(struct xa_state *);
 
 void xas_create_range(struct xa_state *);

lib/xarray.c

@@ -264,9 +264,10 @@ static void xa_node_free(struct xa_node *node)
  * xas_destroy() - Free any resources allocated during the XArray operation.
  * @xas: XArray operation state.
  *
- * This function is now internal-only.
+ * Most users will not need to call this function; it is called for you
+ * by xas_nomem().
  */
-static void xas_destroy(struct xa_state *xas)
+void xas_destroy(struct xa_state *xas)
 {
 	struct xa_node *next, *node = xas->xa_alloc;
 

mm/filemap.c

@@ -2991,11 +2991,12 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
 	struct address_space *mapping = file->f_mapping;
 	DEFINE_READAHEAD(ractl, file, ra, mapping, vmf->pgoff);
 	struct file *fpin = NULL;
+	unsigned long vm_flags = vmf->vma->vm_flags;
 	unsigned int mmap_miss;
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	/* Use the readahead code, even if readahead is disabled */
-	if (vmf->vma->vm_flags & VM_HUGEPAGE) {
+	if (vm_flags & VM_HUGEPAGE) {
 		fpin = maybe_unlock_mmap_for_io(vmf, fpin);
 		ractl._index &= ~((unsigned long)HPAGE_PMD_NR - 1);
 		ra->size = HPAGE_PMD_NR;
@@ -3003,7 +3004,7 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
 		 * Fetch two PMD folios, so we get the chance to actually
 		 * readahead, unless we've been told not to.
 		 */
-		if (!(vmf->vma->vm_flags & VM_RAND_READ))
+		if (!(vm_flags & VM_RAND_READ))
 			ra->size *= 2;
 		ra->async_size = HPAGE_PMD_NR;
 		page_cache_ra_order(&ractl, ra, HPAGE_PMD_ORDER);
@@ -3012,12 +3013,12 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
 #endif
 
 	/* If we don't want any read-ahead, don't bother */
-	if (vmf->vma->vm_flags & VM_RAND_READ)
+	if (vm_flags & VM_RAND_READ)
 		return fpin;
 	if (!ra->ra_pages)
 		return fpin;
 
-	if (vmf->vma->vm_flags & VM_SEQ_READ) {
+	if (vm_flags & VM_SEQ_READ) {
 		fpin = maybe_unlock_mmap_for_io(vmf, fpin);
 		page_cache_sync_ra(&ractl, ra->ra_pages);
 		return fpin;

mm/huge_memory.c

@@ -2672,8 +2672,7 @@ out_unlock:
 	if (mapping)
 		i_mmap_unlock_read(mapping);
 out:
-	/* Free any memory we didn't use */
-	xas_nomem(&xas, 0);
+	xas_destroy(&xas);
 	count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
 	return ret;
 }

mm/readahead.c

@@ -164,12 +164,14 @@ static void read_pages(struct readahead_control *rac)
 		while ((folio = readahead_folio(rac)) != NULL) {
 			unsigned long nr = folio_nr_pages(folio);
 
+			folio_get(folio);
 			rac->ra->size -= nr;
 			if (rac->ra->async_size >= nr) {
 				rac->ra->async_size -= nr;
 				filemap_remove_folio(folio);
 			}
 			folio_unlock(folio);
+			folio_put(folio);
 		}
 	} else {
 		while ((folio = readahead_folio(rac)) != NULL)