mm/filemap: convert filemap_update_page to return an errno

Use AOP_TRUNCATED_PAGE to indicate that no error occurred, but the page we
looked up is no longer valid.  In this case, the reference to the page
will have been removed; if we hit any other error, the caller will release
the reference.

Link: https://lkml.kernel.org/r/20210122160140.223228-12-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Kent Overstreet <kent.overstreet@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/filemap.c b/mm/filemap.c
index c0e5aff..67c4df8 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2233,24 +2233,21 @@ static int filemap_read_page(struct file *file, struct address_space *mapping,
        return error;
 }
 
-static struct page *filemap_update_page(struct kiocb *iocb, struct file *filp,
-               struct iov_iter *iter, struct page *page, loff_t pos,
-               loff_t count)
+static int filemap_update_page(struct kiocb *iocb,
+               struct address_space *mapping, struct iov_iter *iter,
+               struct page *page, loff_t pos, loff_t count)
 {
-       struct address_space *mapping = filp->f_mapping;
        struct inode *inode = mapping->host;
        int error;
 
        if (iocb->ki_flags & IOCB_WAITQ) {
                error = lock_page_async(page, iocb->ki_waitq);
-               if (error) {
-                       put_page(page);
-                       return ERR_PTR(error);
-               }
+               if (error)
+                       return error;
        } else {
                if (!trylock_page(page)) {
                        put_and_wait_on_page_locked(page, TASK_KILLABLE);
-                       return NULL;
+                       return AOP_TRUNCATED_PAGE;
                }
        }
 
@@ -2269,25 +2266,21 @@ static struct page *filemap_update_page(struct kiocb *iocb, struct file *filp,
                goto readpage;
 uptodate:
        unlock_page(page);
-       return page;
+       return 0;
 
 readpage:
        if (iocb->ki_flags & (IOCB_NOIO | IOCB_NOWAIT | IOCB_WAITQ)) {
                unlock_page(page);
-               put_page(page);
-               return ERR_PTR(-EAGAIN);
+               return -EAGAIN;
        }
        error = filemap_read_page(iocb->ki_filp, mapping, page);
-       if (!error)
-               return page;
-       put_page(page);
        if (error == AOP_TRUNCATED_PAGE)
-               return NULL;
-       return ERR_PTR(error);
+               put_page(page);
+       return error;
 truncated:
        unlock_page(page);
        put_page(page);
-       return NULL;
+       return AOP_TRUNCATED_PAGE;
 }
 
 static int filemap_create_page(struct file *file,
@@ -2381,11 +2374,12 @@ got_pages:
                                goto err;
                        }
 
-                       page = filemap_update_page(iocb, filp, iter, page,
+                       err = filemap_update_page(iocb, mapping, iter, page,
                                        pg_pos, pg_count);
-                       if (IS_ERR_OR_NULL(page)) {
+                       if (err) {
+                               if (err < 0)
+                                       put_page(page);
                                pvec->nr--;
-                               err = PTR_ERR_OR_ZERO(page);
                        }
                }
        }
@@ -2393,6 +2387,8 @@ got_pages:
 err:
        if (likely(pvec->nr))
                return 0;
+       if (err == AOP_TRUNCATED_PAGE)
+               goto find_page;
        if (err)
                return err;
        /*