dax: Finish fault completely when loading holes

The only case when we do not finish the page fault completely is when we
are loading hole pages into a radix tree. Avoid this special case and
finish the fault in that case as well inside the DAX fault handler. It
will allow us for easier iomap handling.

Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 18 insertions, 9 deletions

diff --git a/fs/dax.c b/fs/dax.c
index 08e15db28b79..bfec6f2ef613 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -539,15 +539,16 @@ int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
  * otherwise it will simply fall out of the page cache under memory
  * pressure without ever having been dirtied.
  */
-static int dax_load_hole(struct address_space *mapping, void *entry,
+static int dax_load_hole(struct address_space *mapping, void **entry,
                          struct vm_fault *vmf)
 {
         struct page *page;
+        int ret;
 
         /* Hole page already exists? Return it...  */
-        if (!radix_tree_exceptional_entry(entry)) {
-                vmf->page = entry;
-                return VM_FAULT_LOCKED;
+        if (!radix_tree_exceptional_entry(*entry)) {
+                page = *entry;
+                goto out;
         }
 
         /* This will replace locked radix tree entry with a hole page */
@@ -555,8 +556,17 @@ static int dax_load_hole(struct address_space *mapping, void *entry,
                                    vmf->gfp_mask | __GFP_ZERO);
         if (!page)
                 return VM_FAULT_OOM;
+ out:
         vmf->page = page;
-        return VM_FAULT_LOCKED;
+        ret = finish_fault(vmf);
+        vmf->page = NULL;
+        *entry = page;
+        if (!ret) {
+                /* Grab reference for PTE that is now referencing the page */
+                get_page(page);
+                return VM_FAULT_NOPAGE;
+        }
+        return ret;
 }
 
 static int copy_user_dax(struct block_device *bdev, sector_t sector, size_t size,
@@ -1163,8 +1173,8 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
         case IOMAP_UNWRITTEN:
         case IOMAP_HOLE:
                 if (!(vmf->flags & FAULT_FLAG_WRITE)) {
-                        vmf_ret = dax_load_hole(mapping, entry, vmf);
-                        break;
+                        vmf_ret = dax_load_hole(mapping, &entry, vmf);
+                        goto finish_iomap;
                 }
                 /*FALLTHRU*/
         default:
@@ -1185,8 +1195,7 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
                 }
         }
  unlock_entry:
-        if (vmf_ret != VM_FAULT_LOCKED || error)
-                put_locked_mapping_entry(mapping, vmf->pgoff, entry);
+        put_locked_mapping_entry(mapping, vmf->pgoff, entry);
  out:
         if (error == -ENOMEM)
                 return VM_FAULT_OOM | major;