Re: [PATCH 2/8] staging: erofs: separate erofs_get_meta_page

Dan Carpenter
2018-08-13T11:04:34Z

On Sun, Aug 12, 2018 at 10:01:44PM +0800, Chao Yu wrote:
> --- a/drivers/staging/erofs/data.c
> +++ b/drivers/staging/erofs/data.c
> @@ -39,31 +39,44 @@ static inline void read_endio(struct bio *bio)
> }
>
> /* prio -- true is used for dir */
> -struct page *erofs_get_meta_page(struct super_block *sb,
> - erofs_blk_t blkaddr, bool prio)
> +struct page *__erofs_get_meta_page(struct super_block *sb,
> + erofs_blk_t blkaddr, bool prio, bool nofail)
> {
> - struct inode *bd_inode = sb->s_bdev->bd_inode;
> - struct address_space *mapping = bd_inode->i_mapping;
> + struct inode *const bd_inode = sb->s_bdev->bd_inode;
> + struct address_space *const mapping = bd_inode->i_mapping;
> + /* prefer retrying in the allocator to blindly looping below */
> + const gfp_t gfp = mapping_gfp_constraint(mapping, ~__GFP_FS) |
> + (nofail ? __GFP_NOFAIL : 0);
> + unsigned int io_retries = nofail ? EROFS_IO_MAX_RETRIES_NOFAIL : 0;
> struct page *page;
>
> repeat:
> - page = find_or_create_page(mapping, blkaddr,
> - /*
> - * Prefer looping in the allocator rather than here,
> - * at least that code knows what it's doing.
> - */
> - mapping_gfp_constraint(mapping, ~__GFP_FS) | __GFP_NOFAIL);
> -
> - BUG_ON(!page || !PageLocked(page));
> + page = find_or_create_page(mapping, blkaddr, gfp);
> + if (unlikely(page == NULL)) {
> + DBG_BUGON(nofail);
> + return ERR_PTR(-ENOMEM);
> + }
> + DBG_BUGON(!PageLocked(page));
>
> if (!PageUptodate(page)) {
> struct bio *bio;
> int err;
>
> - bio = erofs_grab_bio(sb, blkaddr, 1, read_endio, true);
> + bio = erofs_grab_bio(sb, blkaddr, 1, read_endio, nofail);
> + if (unlikely(bio == NULL)) {
> + DBG_BUGON(nofail);
> + err = -ENOMEM;
> +err_out:
> + unlock_page(page);
> + put_page(page);
> + return ERR_PTR(err);

Put this err_out stuff at the bottom of the function so that we don't
have to do backward hops to get to it.

> + }
>
> err = bio_add_page(bio, page, PAGE_SIZE, 0);
> - BUG_ON(err != PAGE_SIZE);
> + if (unlikely(err != PAGE_SIZE)) {
> + err = -EFAULT;
> + goto err_out;
^^^^^^^^^^^^
Like this. Generally avoid backwards hops if you can.

> + }
>
> __submit_bio(bio, REQ_OP_READ,
> REQ_META | (prio ? REQ_PRIO : 0));
> @@ -72,6 +85,7 @@ struct page *erofs_get_meta_page(struct super_block *sb,
>
> /* the page has been truncated by others? */
> if (unlikely(page->mapping != mapping)) {
> +unlock_repeat:

The question mark in the "truncated by others?" is a little concerning.
It's slightly weird that we don't check "io_retries" on this path.

> unlock_page(page);
> put_page(page);
> goto repeat;
> @@ -79,10 +93,12 @@ struct page *erofs_get_meta_page(struct super_block *sb,
>
> /* more likely a read error */
> if (unlikely(!PageUptodate(page))) {
> - unlock_page(page);
> - put_page(page);
> -
> - page = ERR_PTR(-EIO);
> + if (io_retries) {
> + --io_retries;
> + goto unlock_repeat;
> + }
> + err = -EIO;
> + goto err_out;

regards,
dan carpenter