fs: dcache scale subdirs

Protect d_subdirs and d_child with d_lock, except in filesystems that aren't
using dcache_lock for these anyway (eg. using i_mutex).

Note: if we change the locking rule in future so that ->d_child protection is
provided only with ->d_parent->d_lock, it may allow us to reduce some locking.
But it would be an exception to an otherwise regular locking scheme, so we'd
have to see some good results. Probably not worthwhile.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

1 files changed, 10 insertions, 2 deletions

diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 073fd5b0a53a..017ec096446e 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -1146,22 +1146,30 @@ static void sel_remove_entries(struct dentry *de)
 	struct list_head *node;
 
 	spin_lock(&dcache_lock);
+	spin_lock(&de->d_lock);
 	node = de->d_subdirs.next;
 	while (node != &de->d_subdirs) {
 		struct dentry *d = list_entry(node, struct dentry, d_u.d_child);
+
+		spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED);
 		list_del_init(node);
 
 		if (d->d_inode) {
-			d = dget_locked(d);
+			dget_locked_dlock(d);
+			spin_unlock(&de->d_lock);
+			spin_unlock(&d->d_lock);
 			spin_unlock(&dcache_lock);
 			d_delete(d);
 			simple_unlink(de->d_inode, d);
 			dput(d);
 			spin_lock(&dcache_lock);
-		}
+			spin_lock(&de->d_lock);
+		} else
+			spin_unlock(&d->d_lock);
 		node = de->d_subdirs.next;
 	}
 
+	spin_unlock(&de->d_lock);
 	spin_unlock(&dcache_lock);
 }