fs/buffer: remove __breadahead_gfp()

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 88dbcbb3a484 ("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.com
Signed-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>