[PATCH 15/19] VFS: Change lookup_and_lock() to use shared lock when possible.

[NeilBrown <neilb@xxxxxxx>]

lookup_and_lock() and done_lookup_and_lock() are now told, via LOOKUP_
intent flags what operation is being performed, including a new
LOOKUP_REMOVE.

They use this to determine whether shared or exclusive locking is
needed.

If all filesystems eventually support all async interface, this locking
can be discarded.

Signed-off-by: NeilBrown <neilb@xxxxxxx>
---
 fs/namei.c | 40 ++++++++++++++++++++++++++++++++--------
 1 file changed, 32 insertions(+), 8 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index e8a85c9f431c..c7b7445c770e 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1898,13 +1898,26 @@ static struct dentry *lookup_and_lock_nested(const struct qstr *last,
 					     unsigned int subclass)
 {
 	struct dentry *dentry;
+	unsigned int shared = 0;
 
-	if (!(lookup_flags & LOOKUP_PARENT_LOCKED))
-		inode_lock_nested(base->d_inode, subclass);
+	if (!(lookup_flags & LOOKUP_PARENT_LOCKED)) {
+		if (lookup_flags & LOOKUP_CREATE)
+			shared = S_ASYNC_CREATE;
+		if (lookup_flags & LOOKUP_REMOVE)
+			shared = S_ASYNC_REMOVE;
+
+		if (base->d_inode->i_flags & shared)
+			inode_lock_shared_nested(base->d_inode, subclass);
+		else
+			inode_lock_nested(base->d_inode, subclass);
+	}
 	do {
 		dentry = lookup_one_qstr(last, base, lookup_flags);
 	} while (!IS_ERR(dentry) && !d_update_lock(dentry, base, last, subclass));
 	if (IS_ERR(dentry) && !(lookup_flags & LOOKUP_PARENT_LOCKED)) {
+		if (base->d_inode->i_flags & shared)
+			inode_unlock_shared(base->d_inode);
+		else
 			inode_unlock(base->d_inode);
 	}
 	return dentry;
@@ -1921,11 +1934,22 @@ static struct dentry *lookup_and_lock(const struct qstr *last,
 void done_lookup_and_lock(struct dentry *base, struct dentry *dentry,
 			  unsigned int lookup_flags)
 {
+	unsigned int shared = 0;
+
+	if (lookup_flags & LOOKUP_CREATE)
+		shared = S_ASYNC_CREATE;
+	if (lookup_flags & LOOKUP_REMOVE)
+		shared = S_ASYNC_REMOVE;
+
 	d_lookup_done(dentry);
 	d_update_unlock(dentry);
 	dput(dentry);
-	if (!(lookup_flags & LOOKUP_PARENT_LOCKED))
-		inode_unlock(base->d_inode);
+	if (!(lookup_flags & LOOKUP_PARENT_LOCKED)) {
+		if (base->d_inode->i_flags & shared)
+			inode_unlock_shared(base->d_inode);
+		else
+			inode_unlock(base->d_inode);
+	}
 }
 EXPORT_SYMBOL(done_lookup_and_lock);
 
@@ -4004,7 +4028,7 @@ static const char *open_last_lookups(struct nameidata *nd,
 		 * dropping this one anyway.
 		 */
 	}
-	if (open_flag & O_CREAT)
+	if ((open_flag & O_CREAT) && !(dir->d_inode->i_flags & S_ASYNC_OPEN))
 		inode_lock(dir->d_inode);
 	else
 		inode_lock_shared(dir->d_inode);
@@ -4015,7 +4039,7 @@ static const char *open_last_lookups(struct nameidata *nd,
 		if (file->f_mode & FMODE_OPENED)
 			fsnotify_open(file);
 	}
-	if (open_flag & O_CREAT)
+	if ((open_flag & O_CREAT) && !(dir->d_inode->i_flags & S_ASYNC_OPEN))
 		inode_unlock(dir->d_inode);
 	else
 		inode_unlock_shared(dir->d_inode);
@@ -4775,7 +4799,7 @@ int do_rmdir(int dfd, struct filename *name)
 	struct path path;
 	struct qstr last;
 	int type;
-	unsigned int lookup_flags = 0;
+	unsigned int lookup_flags = LOOKUP_REMOVE;
 retry:
 	error = filename_parentat(dfd, name, lookup_flags, &path, &last, &type);
 	if (error)
@@ -4914,7 +4938,7 @@ int do_unlinkat(int dfd, struct filename *name)
 	int type;
 	struct inode *inode = NULL;
 	struct inode *delegated_inode = NULL;
-	unsigned int lookup_flags = 0;
+	unsigned int lookup_flags = LOOKUP_REMOVE;
 retry:
 	error = filename_parentat(dfd, name, lookup_flags, &path, &last, &type);
 	if (error)
-- 
2.47.1