fs/buffer: remove __breadahead_gfp()

Patch series "fs/buffer: remove ll_rw_block()", v2.

ll_rw_block() will skip locked buffer before submitting IO, it assumes
that locked buffer means it is under IO.  This assumption is not always
true because we cannot guarantee every buffer lock path would submit IO. 
After commit 88dbcbb3 ("blkdev: avoid migration stalls for blkdev
pages"), buffer_migrate_folio_norefs() becomes one exceptional case, and
there may be others.  So ll_rw_block() is not safe on the sync read path,
we could get false positive EIO return value when filesystem reading
metadata.  It seems that it could be only used on the readahead path.

Unfortunately, many filesystem misuse the ll_rw_block() on the sync read
path.  This patch set just remove ll_rw_block() and add new friendly
helpers, which could prevent false positive EIO on the read metadata path.
Thanks for the suggestion from Jan, the original discussion is at [1].

 patch 1: remove unused helpers in fs/buffer.c
 patch 2: add new bh_read_[*] helpers
 patch 3-11: remove all ll_rw_block() calls in filesystems
 patch 12-14: do some leftover cleanups.

[1]. https://lore.kernel.org/linux-mm/20220825080146.2021641-1-chengzhihao1@huawei.com/


This patch (of 14):

No one use __breadahead_gfp() and sb_breadahead_unmovable() any more,
remove them.

Link: https://lkml.kernel.org/r/20220901133505.2510834-1-yi.zhang@huawei.com
Link: https://lkml.kernel.org/r/20220901133505.2510834-2-yi.zhang@huawei.comSigned-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Bob Peterson <rpeterso@redhat.com>
Cc: Evgeniy Dushistov <dushistov@mail.ru>
Cc: Heming Zhao <ocfs2-devel@oss.oracle.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Yu Kuai <yukuai3@huawei.com>
Cc: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/buffer.c

@@ -1348,17 +1348,6 @@ void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
 }
 EXPORT_SYMBOL(__breadahead);
 
-void __breadahead_gfp(struct block_device *bdev, sector_t block, unsigned size,
-		      gfp_t gfp)
-{
-	struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
-	if (likely(bh)) {
-		ll_rw_block(REQ_OP_READ | REQ_RAHEAD, 1, &bh);
-		brelse(bh);
-	}
-}
-EXPORT_SYMBOL(__breadahead_gfp);
-
 /**
  *  __bread_gfp() - reads a specified block and returns the bh
  *  @bdev: the block_device to read from

include/linux/buffer_head.h

@@ -214,8 +214,6 @@ struct buffer_head *__getblk_gfp(struct block_device *bdev, sector_t block,
 void __brelse(struct buffer_head *);
 void __bforget(struct buffer_head *);
 void __breadahead(struct block_device *, sector_t block, unsigned int size);
-void __breadahead_gfp(struct block_device *, sector_t block, unsigned int size,
-		  gfp_t gfp);
 struct buffer_head *__bread_gfp(struct block_device *,
 				sector_t block, unsigned size, gfp_t gfp);
 void invalidate_bh_lrus(void);
@@ -340,12 +338,6 @@ sb_breadahead(struct super_block *sb, sector_t block)
 	__breadahead(sb->s_bdev, block, sb->s_blocksize);
 }
 
-static inline void
-sb_breadahead_unmovable(struct super_block *sb, sector_t block)
-{
-	__breadahead_gfp(sb->s_bdev, block, sb->s_blocksize, 0);
-}
-
 static inline struct buffer_head *
 sb_getblk(struct super_block *sb, sector_t block)
 {