[patch 21/28] fs: dcache reduce locking in d_alloc

[Nick Piggin <npiggin@kernel.dk>]

[-- Attachment #1: fs-dcache-d_alloc-less-d_lock.patch --]
[-- Type: text/plain, Size: 823 bytes --]

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

---
 fs/dcache.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Index: linux-2.6/fs/dcache.c
===================================================================
--- linux-2.6.orig/fs/dcache.c	2010-11-17 00:52:37.000000000 +1100
+++ linux-2.6/fs/dcache.c	2010-11-17 01:05:39.000000000 +1100
@@ -1220,11 +1220,13 @@ struct dentry *d_alloc(struct dentry * p
 
 	if (parent) {
 		spin_lock(&parent->d_lock);
-		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
+		/*
+		 * don't need child lock because it is not subject
+		 * to concurrency here
+		 */
 		dentry->d_parent = dget_dlock(parent);
 		dentry->d_sb = parent->d_sb;
 		list_add(&dentry->d_u.d_child, &parent->d_subdirs);
-		spin_unlock(&dentry->d_lock);
 		spin_unlock(&parent->d_lock);
 	}