From: Maneesh Soni <maneesh@in.ibm.com>
o The following patch fixes is_subdir() races with d_move. Due to concurrent
d_move, in is_subdir() we can end up accessing freed d_parent pointer in
case of pre-emptible kernel. To avoid this we can use rcu_read_lock() and
rcu_read_unlock().
o This also fixes the seqlock uses in is_subdir() as we need to restart the
the inner loop with the origianl new_dentry passed to the routine in case
of any rename occured while we are traversing d_parent links.
---
fs/dcache.c | 9 +++++++++
1 files changed, 9 insertions(+)
diff -puN fs/dcache.c~is_subdir-locking-fix fs/dcache.c
--- 25/fs/dcache.c~is_subdir-locking-fix 2004-01-27 23:45:49.000000000 -0800
+++ 25-akpm/fs/dcache.c 2004-01-27 23:45:49.000000000 -0800
@@ -1434,15 +1434,23 @@ out:
*
* Returns 1 if new_dentry is a subdirectory of the parent (at any depth).
* Returns 0 otherwise.
+ * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
*/
int is_subdir(struct dentry * new_dentry, struct dentry * old_dentry)
{
int result;
+ struct dentry * saved = new_dentry;
unsigned long seq;
result = 0;
+ /* need rcu_readlock to protect against the d_parent trashing due to
+ * d_move
+ */
+ rcu_read_lock();
do {
+ /* for restarting inner loop in case of seq retry */
+ new_dentry = saved;
seq = read_seqbegin(&rename_lock);
for (;;) {
if (new_dentry != old_dentry) {
@@ -1456,6 +1464,7 @@ int is_subdir(struct dentry * new_dentry
break;
}
} while (read_seqretry(&rename_lock, seq));
+ rcu_read_unlock();
return result;
}
_