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>

2 files changed, 9 insertions, 3 deletions

diff --git a/drivers/staging/smbfs/cache.c b/drivers/staging/smbfs/cache.c
index 0beded260b00..920434b6c071 100644
--- a/drivers/staging/smbfs/cache.c
+++ b/drivers/staging/smbfs/cache.c
@@ -63,6 +63,7 @@ smb_invalidate_dircache_entries(struct dentry *parent)
 	struct dentry *dentry;
 
 	spin_lock(&dcache_lock);
+	spin_lock(&parent->d_lock);
 	next = parent->d_subdirs.next;
 	while (next != &parent->d_subdirs) {
 		dentry = list_entry(next, struct dentry, d_u.d_child);
@@ -70,6 +71,7 @@ smb_invalidate_dircache_entries(struct dentry *parent)
 		smb_age_dentry(server, dentry);
 		next = next->next;
 	}
+	spin_unlock(&parent->d_lock);
 	spin_unlock(&dcache_lock);
 }
 
@@ -97,6 +99,7 @@ smb_dget_fpos(struct dentry *dentry, struct dentry *parent, unsigned long fpos)
 
 	/* If a pointer is invalid, we search the dentry. */
 	spin_lock(&dcache_lock);
+	spin_lock(&parent->d_lock);
 	next = parent->d_subdirs.next;
 	while (next != &parent->d_subdirs) {
 		dent = list_entry(next, struct dentry, d_u.d_child);
@@ -111,6 +114,7 @@ smb_dget_fpos(struct dentry *dentry, struct dentry *parent, unsigned long fpos)
 	}
 	dent = NULL;
 out_unlock:
+	spin_unlock(&parent->d_lock);
 	spin_unlock(&dcache_lock);
 	return dent;
 }
diff --git a/drivers/usb/core/inode.c b/drivers/usb/core/inode.c
index e3ab4437ea96..89a0e8366585 100644
--- a/drivers/usb/core/inode.c
+++ b/drivers/usb/core/inode.c
@@ -344,18 +344,20 @@ static int usbfs_empty (struct dentry *dentry)
 	struct list_head *list;
 
 	spin_lock(&dcache_lock);
-
+	spin_lock(&dentry->d_lock);
 	list_for_each(list, &dentry->d_subdirs) {
 		struct dentry *de = list_entry(list, struct dentry, d_u.d_child);
-		spin_lock(&de->d_lock);
+
+		spin_lock_nested(&de->d_lock, DENTRY_D_LOCK_NESTED);
 		if (usbfs_positive(de)) {
 			spin_unlock(&de->d_lock);
+			spin_unlock(&dentry->d_lock);
 			spin_unlock(&dcache_lock);
 			return 0;
 		}
 		spin_unlock(&de->d_lock);
 	}
-
+	spin_unlock(&dentry->d_lock);
 	spin_unlock(&dcache_lock);
 	return 1;
 }