[PATCH v3 2/3] jffs2: jffs2_iget defer f->sem acquisition

[Helmut Grohne <helmut.grohne@xxxxxxxxxx>]

At the point where f->sem is taken, we know that we have a locked I_NEW
inode. Since jffs2_iget is the only function processing I_NEW inodes and
iget_locked blocks on I_NEW inodes, we know that we are the only user of
the inode until we unlock_new_inode it. Since 7aaea7605c0 ("jffs2: fix
unbalanced locking"), jffs2_do_read_inode no longer touches f->sem and
does not make the inode visible to others either. Thus we can call it
without f->sem acquired. Nextup, inode->i_mode is protected until
unlock_new_inode.

After deferring the locking, we can decide upon the proper lock class
depending on inode->i_mode.

Signed-off-by: Helmut Grohne <helmut.grohne@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Reviewed-by: Richard Weinberger <richard@xxxxxx>
---
 fs/jffs2/fs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/jffs2/fs.c b/fs/jffs2/fs.c
index eab04eca95a3..89a10b398d00 100644
--- a/fs/jffs2/fs.c
+++ b/fs/jffs2/fs.c
@@ -270,13 +270,15 @@ struct inode *jffs2_iget(struct super_block *sb, unsigned long ino)
 	c = JFFS2_SB_INFO(inode->i_sb);
 
 	jffs2_init_inode_info(f);
-	mutex_lock(&f->sem);
 
 	ret = jffs2_do_read_inode(c, f, inode->i_ino, &latest_node);
 	if (ret)
 		goto error;
 
 	inode->i_mode = jemode_to_cpu(latest_node.mode);
+
+	mutex_lock(&f->sem);
+
 	i_uid_write(inode, je16_to_cpu(latest_node.uid));
 	i_gid_write(inode, je16_to_cpu(latest_node.gid));
 	inode->i_size = je32_to_cpu(latest_node.isize);
-- 
2.11.0


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