Use RCU to simplify locking in dget_parent.
Signed-off-by: Nick Piggin <npiggin@xxxxxxxxx>
---
fs/dcache.c | 25 ++++++++++++++-----------
1 file changed, 14 insertions(+), 11 deletions(-)
Index: linux-2.6/fs/dcache.c
===================================================================
--- linux-2.6.orig/fs/dcache.c 2010-11-17 00:52:38.000000000 +1100
+++ linux-2.6/fs/dcache.c 2010-11-17 01:05:38.000000000 +1100
@@ -406,24 +406,27 @@ struct dentry *dget_parent(struct dentry
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++;
- goto out;
- }
- if (!spin_trylock(&ret->d_lock)) {
- spin_unlock(&dentry->d_lock);
- cpu_relax();
+ if (!ret) {
+ rcu_read_unlock();
+ goto out;
+ }
+ 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);
--
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