[PATCH v3 08/11] nfs: Don't hold i_lock while walking ->d_children list

[NeilBrown]

From: NeilBrown <neil@xxxxxxxxxx>

Instead of taking i_lock in nfs_clear_verifier_delegated(), take it only
when it is actually needed.
This means i_lock isn't held while testing the type S_IFMT of the inode,
but that cannot change so it doesn't matter.

In nfs_clear_verifier_file(), simply take i_lock for the whole function
while enumerating the aliases.

In nfs_clear_verifier_directory(), use d_find_alias() (which takes
i_lock) to find and get the one alias, then dput() it when we are done.

The import result here is that we don't hold any other spinlock when
walking the d_children list.

Signed-off-by: NeilBrown <neil@xxxxxxxxxx>
---
 fs/nfs/dir.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 748c8388c4f0..a5f6fa57fa39 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1469,6 +1469,7 @@ static void nfs_clear_verifier_file(struct inode *inode)
 	struct dentry *alias;
 	struct inode *dir;
 
+	guard(spinlock)(&inode->i_lock);
 	for_each_alias(alias, inode) {
 		spin_lock(&alias->d_lock);
 		dir = d_inode_rcu(alias->d_parent);
@@ -1485,10 +1486,9 @@ static void nfs_clear_verifier_directory(struct inode *dir)
 	struct dentry *dentry;
 	struct inode *inode;
 
-	if (hlist_empty(&dir->i_dentry))
+	this_parent = d_find_alias(dir);
+	if (!this_parent)
 		return;
-	this_parent =
-		hlist_entry(dir->i_dentry.first, struct dentry, d_alias);
 
 	spin_lock(&this_parent->d_lock);
 	nfs_unset_verifier_delegated(&this_parent->d_time);
@@ -1503,6 +1503,7 @@ static void nfs_clear_verifier_directory(struct inode *dir)
 		nfs_unset_verifier_delegated(&dentry->d_time);
 		spin_unlock(&dentry->d_lock);
 	}
+	dput(this_parent);
 }
 
 /**
@@ -1519,12 +1520,10 @@ void nfs_clear_verifier_delegated(struct inode *inode)
 {
 	if (!inode)
 		return;
-	spin_lock(&inode->i_lock);
 	if (S_ISREG(inode->i_mode))
 		nfs_clear_verifier_file(inode);
 	else if (S_ISDIR(inode->i_mode))
 		nfs_clear_verifier_directory(inode);
-	spin_unlock(&inode->i_lock);
 }
 EXPORT_SYMBOL_GPL(nfs_clear_verifier_delegated);
 #endif /* IS_ENABLED(CONFIG_NFS_V4) */
-- 
2.50.0.107.gf914562f5916.dirty