nilfs2: localize highmem mapping for checkpoint creation within cpfile

In order to convert kmap() used in cpfile to kmap_local, first move the
checkpoint creation routine, which is one of the places where kmap is
used, to the cpfile side and make the page mapping local and temporary. 
And use kmap_local instead of kmap to access the checkpoint entry page
(and header block page) when generating a checkpoint.

Link: https://lkml.kernel.org/r/20240122140202.6950-12-konishi.ryusuke@gmail.comSigned-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/nilfs2/cpfile.c

@@ -272,6 +272,80 @@ int nilfs_cpfile_get_checkpoint(struct inode *cpfile,
 	return ret;
 }
 
+/**
+ * nilfs_cpfile_create_checkpoint - create a checkpoint entry on cpfile
+ * @cpfile: checkpoint file inode
+ * @cno:    number of checkpoint to set up
+ *
+ * This function creates a checkpoint with the number specified by @cno on
+ * cpfile.  If the specified checkpoint entry already exists due to a past
+ * failure, it will be reused without returning an error.
+ * In either case, the buffer of the block containing the checkpoint entry
+ * and the cpfile inode are made dirty for inclusion in the write log.
+ *
+ * Return: 0 on success, or the following negative error code on failure.
+ * * %-ENOMEM	- Insufficient memory available.
+ * * %-EIO	- I/O error (including metadata corruption).
+ * * %-EROFS	- Read only filesystem
+ */
+int nilfs_cpfile_create_checkpoint(struct inode *cpfile, __u64 cno)
+{
+	struct buffer_head *header_bh, *cp_bh;
+	struct nilfs_cpfile_header *header;
+	struct nilfs_checkpoint *cp;
+	void *kaddr;
+	int ret;
+
+	if (WARN_ON_ONCE(cno < 1))
+		return -EIO;
+
+	down_write(&NILFS_MDT(cpfile)->mi_sem);
+	ret = nilfs_cpfile_get_header_block(cpfile, &header_bh);
+	if (unlikely(ret < 0)) {
+		if (ret == -ENOENT) {
+			nilfs_error(cpfile->i_sb,
+				    "checkpoint creation failed due to metadata corruption.");
+			ret = -EIO;
+		}
+		goto out_sem;
+	}
+	ret = nilfs_cpfile_get_checkpoint_block(cpfile, cno, 1, &cp_bh);
+	if (unlikely(ret < 0))
+		goto out_header;
+
+	kaddr = kmap_local_page(cp_bh->b_page);
+	cp = nilfs_cpfile_block_get_checkpoint(cpfile, cno, cp_bh, kaddr);
+	if (nilfs_checkpoint_invalid(cp)) {
+		/* a newly-created checkpoint */
+		nilfs_checkpoint_clear_invalid(cp);
+		if (!nilfs_cpfile_is_in_first(cpfile, cno))
+			nilfs_cpfile_block_add_valid_checkpoints(cpfile, cp_bh,
+								 kaddr, 1);
+		kunmap_local(kaddr);
+
+		kaddr = kmap_local_page(header_bh->b_page);
+		header = nilfs_cpfile_block_get_header(cpfile, header_bh,
+						       kaddr);
+		le64_add_cpu(&header->ch_ncheckpoints, 1);
+		kunmap_local(kaddr);
+		mark_buffer_dirty(header_bh);
+	} else {
+		kunmap_local(kaddr);
+	}
+
+	/* Force the buffer and the inode to become dirty */
+	mark_buffer_dirty(cp_bh);
+	brelse(cp_bh);
+	nilfs_mdt_mark_dirty(cpfile);
+
+out_header:
+	brelse(header_bh);
+
+out_sem:
+	up_write(&NILFS_MDT(cpfile)->mi_sem);
+	return ret;
+}
+
 /**
  * nilfs_cpfile_put_checkpoint - put a checkpoint
  * @cpfile: inode of checkpoint file

fs/nilfs2/cpfile.h

@@ -19,6 +19,7 @@
 int nilfs_cpfile_get_checkpoint(struct inode *, __u64, int,
 				struct nilfs_checkpoint **,
 				struct buffer_head **);
+int nilfs_cpfile_create_checkpoint(struct inode *cpfile, __u64 cno);
 void nilfs_cpfile_put_checkpoint(struct inode *, __u64, struct buffer_head *);
 int nilfs_cpfile_delete_checkpoints(struct inode *, __u64, __u64);
 int nilfs_cpfile_delete_checkpoint(struct inode *, __u64);

fs/nilfs2/segment.c

@@ -880,34 +880,6 @@ static void nilfs_segctor_clear_metadata_dirty(struct nilfs_sc_info *sci)
 	nilfs_mdt_clear_dirty(nilfs->ns_dat);
 }
 
-static int nilfs_segctor_create_checkpoint(struct nilfs_sc_info *sci)
-{
-	struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
-	struct buffer_head *bh_cp;
-	struct nilfs_checkpoint *raw_cp;
-	int err;
-
-	/* XXX: this interface will be changed */
-	err = nilfs_cpfile_get_checkpoint(nilfs->ns_cpfile, nilfs->ns_cno, 1,
-					  &raw_cp, &bh_cp);
-	if (likely(!err)) {
-		/*
-		 * The following code is duplicated with cpfile.  But, it is
-		 * needed to collect the checkpoint even if it was not newly
-		 * created.
-		 */
-		mark_buffer_dirty(bh_cp);
-		nilfs_mdt_mark_dirty(nilfs->ns_cpfile);
-		nilfs_cpfile_put_checkpoint(
-			nilfs->ns_cpfile, nilfs->ns_cno, bh_cp);
-	} else if (err == -EINVAL || err == -ENOENT) {
-		nilfs_error(sci->sc_super,
-			    "checkpoint creation failed due to metadata corruption.");
-		err = -EIO;
-	}
-	return err;
-}
-
 static int nilfs_segctor_fill_in_checkpoint(struct nilfs_sc_info *sci)
 {
 	struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
@@ -1261,7 +1233,8 @@ static int nilfs_segctor_collect_blocks(struct nilfs_sc_info *sci, int mode)
 			break;
 		nilfs_sc_cstage_inc(sci);
 		/* Creating a checkpoint */
-		err = nilfs_segctor_create_checkpoint(sci);
+		err = nilfs_cpfile_create_checkpoint(nilfs->ns_cpfile,
+						     nilfs->ns_cno);
 		if (unlikely(err))
 			break;
 		fallthrough;