On Sat 23-12-23 17:31:55, Matthew Wilcox wrote: > 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. In principle I agree with you but in this particular case I agree the ask is just too big. I suspect it is one of btrfs btree locks or maybe chunk_mutex but I doubt even btrfs developers know and maybe it is just a cargo cult. And it is not like this would be the first occurence of this anti-pattern in btrfs - see e.g. device_list_add(), add_missing_dev(), btrfs_destroy_delalloc_inodes() (here the wrapping around invalidate_inode_pages2() looks really weird), and many others... Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
