fs: dcache reduce d_parent locking
Use RCU to simplify locking in dget_parent.
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
diff --git a/fs/dcache.c b/fs/dcache.c
index b4d2e28..a8f8976 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -446,24 +446,27 @@
struct dentry *ret;
repeat:
- spin_lock(&dentry->d_lock);
+ /*
+ * Don't need rcu_dereference because we re-check it was correct under
+ * the lock.
+ */
+ rcu_read_lock();
ret = dentry->d_parent;
- if (!ret)
- goto out;
- if (dentry == ret) {
- ret->d_count++;
+ if (!ret) {
+ rcu_read_unlock();
goto out;
}
- if (!spin_trylock(&ret->d_lock)) {
- spin_unlock(&dentry->d_lock);
- cpu_relax();
+ spin_lock(&ret->d_lock);
+ if (unlikely(ret != dentry->d_parent)) {
+ spin_unlock(&ret->d_lock);
+ rcu_read_unlock();
goto repeat;
}
+ rcu_read_unlock();
BUG_ON(!ret->d_count);
ret->d_count++;
spin_unlock(&ret->d_lock);
out:
- spin_unlock(&dentry->d_lock);
return ret;
}
EXPORT_SYMBOL(dget_parent);