[Cluster-devel] [GFS2 PATCH 10/15] gfs2: replace sd_aspace with sd_inode

[Bob Peterson <rpeterso@redhat.com>]

Before this patch, gfs2 kept its own address space for rgrps, but this
caused a lockdep problem because vfs assumes a 1:1 relationship between
address spaces and their inode. One problematic area is this:

gfs2_unpin
   mark_buffer_dirty(bh);
      mapping = page_mapping(page);
         __set_page_dirty(page, mapping, memcg, 0);
            xa_lock_irqsave(&mapping->i_pages, flags);
                 ^---locks page->mapping->i_pages
            account_page_dirtied(page, mapping)
	       struct inode *inode = mapping->host;
                 ^---assumes the mapping points to an inode
               inode_to_wb(inode)
                  WARN_ON_ONCE !lockdep_is_held(&inode->i_mapping->
                                                i_pages.xa_lock)

It manifests as a lockdep warning you see in the last line.

This patch removes sd_aspace in favor of an entire inode, sd_inode.
Functions that need to access the address space may use a new function
that follows the inode to its address space. This creates the 1:1 relation
between the inode and its address space, so lockdep doesn't complain.
This is how some other file systems manage their metadata, such as btrfs.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
---
 fs/gfs2/glops.c      |  4 ++--
 fs/gfs2/incore.h     |  7 ++++++-
 fs/gfs2/meta_io.c    |  2 +-
 fs/gfs2/meta_io.h    |  2 --
 fs/gfs2/ops_fstype.c | 27 ++++++++++++++++-----------
 fs/gfs2/super.c      |  2 +-
 6 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/fs/gfs2/glops.c b/fs/gfs2/glops.c
index 744cacd27213..5d755d30d91c 100644
--- a/fs/gfs2/glops.c
+++ b/fs/gfs2/glops.c
@@ -162,7 +162,7 @@ void gfs2_ail_flush(struct gfs2_glock *gl, bool fsync)
 static int gfs2_rgrp_metasync(struct gfs2_glock *gl)
 {
 	struct gfs2_sbd *sdp = gl->gl_name.ln_sbd;
-	struct address_space *metamapping = &sdp->sd_aspace;
+	struct address_space *metamapping = gfs2_aspace(sdp);
 	struct gfs2_rgrpd *rgd = gfs2_glock2rgrp(gl);
 	const unsigned bsize = sdp->sd_sb.sb_bsize;
 	loff_t start = (rgd->rd_addr * bsize) & PAGE_MASK;
@@ -219,7 +219,7 @@ static int rgrp_go_sync(struct gfs2_glock *gl)
 static void rgrp_go_inval(struct gfs2_glock *gl, int flags)
 {
 	struct gfs2_sbd *sdp = gl->gl_name.ln_sbd;
-	struct address_space *mapping = &sdp->sd_aspace;
+	struct address_space *mapping = gfs2_aspace(sdp);
 	struct gfs2_rgrpd *rgd = gfs2_glock2rgrp(gl);
 	const unsigned bsize = sdp->sd_sb.sb_bsize;
 	loff_t start = (rgd->rd_addr * bsize) & PAGE_MASK;
diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 6f31a067a5f2..4a03c3031347 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -795,7 +795,7 @@ struct gfs2_sbd {
 
 	/* Log stuff */
 
-	struct address_space sd_aspace;
+	struct inode *sd_inode;
 
 	spinlock_t sd_log_lock;
 
@@ -851,6 +851,11 @@ struct gfs2_sbd {
 	unsigned long sd_glock_dqs_held;
 };
 
+static inline struct address_space *gfs2_aspace(struct gfs2_sbd *sdp)
+{
+	return sdp->sd_inode->i_mapping;
+}
+
 static inline void gfs2_glstats_inc(struct gfs2_glock *gl, int which)
 {
 	gl->gl_stats.stats[which]++;
diff --git a/fs/gfs2/meta_io.c b/fs/gfs2/meta_io.c
index 7c9619997355..0123437d9c12 100644
--- a/fs/gfs2/meta_io.c
+++ b/fs/gfs2/meta_io.c
@@ -120,7 +120,7 @@ struct buffer_head *gfs2_getbuf(struct gfs2_glock *gl, u64 blkno, int create)
 	unsigned int bufnum;
 
 	if (mapping == NULL)
-		mapping = &sdp->sd_aspace;
+		mapping = gfs2_aspace(sdp);
 
 	shift = PAGE_SHIFT - sdp->sd_sb.sb_bsize_shift;
 	index = blkno >> shift;             /* convert block to page */
diff --git a/fs/gfs2/meta_io.h b/fs/gfs2/meta_io.h
index 21880d72081a..70b9c41ecb46 100644
--- a/fs/gfs2/meta_io.h
+++ b/fs/gfs2/meta_io.h
@@ -42,8 +42,6 @@ static inline struct gfs2_sbd *gfs2_mapping2sbd(struct address_space *mapping)
 	struct inode *inode = mapping->host;
 	if (mapping->a_ops == &gfs2_meta_aops)
 		return (((struct gfs2_glock *)mapping) - 1)->gl_name.ln_sbd;
-	else if (mapping->a_ops == &gfs2_rgrp_aops)
-		return container_of(mapping, struct gfs2_sbd, sd_aspace);
 	else
 		return inode->i_sb->s_fs_info;
 }
diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 5b90d2b7db47..8051f130cf53 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -72,7 +72,6 @@ void free_sbd(struct gfs2_sbd *sdp)
 static struct gfs2_sbd *init_sbd(struct super_block *sb)
 {
 	struct gfs2_sbd *sdp;
-	struct address_space *mapping;
 
 	sdp = kzalloc(sizeof(struct gfs2_sbd), GFP_KERNEL);
 	if (!sdp)
@@ -112,16 +111,6 @@ static struct gfs2_sbd *init_sbd(struct super_block *sb)
 
 	INIT_LIST_HEAD(&sdp->sd_sc_inodes_list);
 
-	mapping = &sdp->sd_aspace;
-
-	address_space_init_once(mapping);
-	mapping->a_ops = &gfs2_rgrp_aops;
-	mapping->host = sb->s_bdev->bd_inode;
-	mapping->flags = 0;
-	mapping_set_gfp_mask(mapping, GFP_NOFS);
-	mapping->private_data = NULL;
-	mapping->writeback_index = 0;
-
 	spin_lock_init(&sdp->sd_log_lock);
 	atomic_set(&sdp->sd_log_pinned, 0);
 	INIT_LIST_HEAD(&sdp->sd_log_revokes);
@@ -1140,6 +1129,7 @@ static int gfs2_fill_super(struct super_block *sb, struct fs_context *fc)
 	struct gfs2_sbd *sdp;
 	struct gfs2_holder mount_gh;
 	struct gfs2_holder freeze_gh;
+	struct address_space *mapping;
 	int error;
 
 	sdp = init_sbd(sb);
@@ -1161,6 +1151,21 @@ static int gfs2_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_flags |= SB_NOSEC;
 	sb->s_magic = GFS2_MAGIC;
 	sb->s_op = &gfs2_super_ops;
+
+	/* Set up an address space for metadata writes */
+	sdp->sd_inode = new_inode(sb);
+	if (!sdp->sd_inode)
+		goto fail_free;
+	sdp->sd_inode->i_ino = GFS2_MAGIC;
+	set_nlink(sdp->sd_inode, 1);
+	sdp->sd_inode->i_size = i_size_read(sb->s_bdev->bd_inode);
+	insert_inode_hash(sdp->sd_inode);
+
+	mapping = gfs2_aspace(sdp);
+	mapping->a_ops = &gfs2_rgrp_aops;
+	mapping_set_gfp_mask(mapping, GFP_NOFS);
+	mapping->writeback_index = 0;
+
 	sb->s_d_op = &gfs2_dops;
 	sb->s_export_op = &gfs2_export_ops;
 	sb->s_qcop = &gfs2_quotactl_ops;
diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 0a5b7dfa7a45..9857d8725b2d 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -617,13 +617,13 @@ static void gfs2_put_super(struct super_block *sb)
 	gfs2_jindex_free(sdp);
 	/*  Take apart glock structures and buffer lists  */
 	gfs2_gl_hash_clear(sdp);
-	truncate_inode_pages_final(&sdp->sd_aspace);
 	gfs2_delete_debugfs_file(sdp);
 	/*  Unmount the locking protocol  */
 	gfs2_lm_unmount(sdp);
 
 	/*  At this point, we're through participating in the lockspace  */
 	gfs2_sys_fs_del(sdp);
+	iput(sdp->sd_inode);
 	free_sbd(sdp);
 }
 
-- 
2.31.1