Re: [PATCH RFC v3 for-6.8/block 09/17] btrfs: use bdev apis

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Thu, Dec 21, 2023 at 04:57:04PM +0800, Yu Kuai wrote:
> @@ -3674,16 +3670,17 @@ struct btrfs_super_block 
> *btrfs_read_dev_one_super(struct block_device *bdev,
>                * Drop the page of the primary superblock, so later read will
>                * always read from the device.
>                */
> -             invalidate_inode_pages2_range(mapping,
> -                             bytenr >> PAGE_SHIFT,
> +             invalidate_bdev_range(bdev, bytenr >> PAGE_SHIFT,
>                               (bytenr + BTRFS_SUPER_INFO_SIZE) >> PAGE_SHIFT);
>       }
>  
> -     page = read_cache_page_gfp(mapping, bytenr >> PAGE_SHIFT, GFP_NOFS);
> -     if (IS_ERR(page))
> -             return ERR_CAST(page);
> +     nofs_flag = memalloc_nofs_save();
> +     folio = bdev_read_folio(bdev, bytenr);
> +     memalloc_nofs_restore(nofs_flag);

This is the wrong way to use memalloc_nofs_save/restore.  They should be
used at the point that the filesystem takes/releases whatever lock is
also used during reclaim.  I don't know btrfs well enough to suggest
what lock is missing these annotations.