fs/buffer: add some new buffer read helpers

Current ll_rw_block() helper is fragile because it assumes that locked
buffer means it's under IO which is submitted by some other who holds
the lock, it skip buffer if it failed to get the lock, so it's only
safe on the readahead path. Unfortunately, now that most filesystems
still use this helper mistakenly on the sync metadata read path. There
is no guarantee that the one who holds the buffer lock always submit IO
(e.g. buffer_migrate_folio_norefs() after commit 88dbcbb3a484 ("blkdev:
avoid migration stalls for blkdev pages"), it could lead to false
positive -EIO when submitting reading IO.

This patch add some friendly buffer read helpers to prepare replacing
ll_rw_block() and similar calls. We can only call bh_readahead_[]
helpers for the readahead paths.

Link: https://lkml.kernel.org/r/20220901133505.2510834-3-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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 38 insertions, 0 deletions

diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index c3863c417b00..6d09785bed9f 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -232,6 +232,9 @@ void write_boundary_block(struct block_device *bdev,
 			sector_t bblock, unsigned blocksize);
 int bh_uptodate_or_lock(struct buffer_head *bh);
 int bh_submit_read(struct buffer_head *bh);
+int __bh_read(struct buffer_head *bh, blk_opf_t op_flags, bool wait);
+void __bh_read_batch(int nr, struct buffer_head *bhs[],
+		     blk_opf_t op_flags, bool force_lock);
 
 extern int buffer_heads_over_limit;
 
@@ -399,6 +402,41 @@ static inline struct buffer_head *__getblk(struct block_device *bdev,
 	return __getblk_gfp(bdev, block, size, __GFP_MOVABLE);
 }
 
+static inline void bh_readahead(struct buffer_head *bh, blk_opf_t op_flags)
+{
+	if (!buffer_uptodate(bh) && trylock_buffer(bh)) {
+		if (!buffer_uptodate(bh))
+			__bh_read(bh, op_flags, false);
+		else
+			unlock_buffer(bh);
+	}
+}
+
+static inline void bh_read_nowait(struct buffer_head *bh, blk_opf_t op_flags)
+{
+	if (!bh_uptodate_or_lock(bh))
+		__bh_read(bh, op_flags, false);
+}
+
+/* Returns 1 if buffer uptodated, 0 on success, and -EIO on error. */
+static inline int bh_read(struct buffer_head *bh, blk_opf_t op_flags)
+{
+	if (bh_uptodate_or_lock(bh))
+		return 1;
+	return __bh_read(bh, op_flags, true);
+}
+
+static inline void bh_read_batch(int nr, struct buffer_head *bhs[])
+{
+	__bh_read_batch(nr, bhs, 0, true);
+}
+
+static inline void bh_readahead_batch(int nr, struct buffer_head *bhs[],
+				      blk_opf_t op_flags)
+{
+	__bh_read_batch(nr, bhs, op_flags, false);
+}
+
 /**
  *  __bread() - reads a specified block and returns the bh
  *  @bdev: the block_device to read from