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-fix fs/dcache.c
--- linux-2.6.2-rc2/fs/dcache.c~is_subdir-fix 2004-01-27 22:38:17.000000000 +0530
+++ linux-2.6.2-rc2-maneesh/fs/dcache.c 2004-01-27 23:43:17.000000000 +0530
@@ -1429,15 +1429,23 @@ 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) {
@@ -1451,6 +1459,7 @@ int is_subdir(struct dentry * new_dentry
break;
}
} while (read_seqretry(&rename_lock, seq));
+ rcu_read_unlock();
return result;
}
_
--
Maneesh Soni
Linux Technology Center,
IBM Software Lab, Bangalore, India
email: maneesh _at_ in.ibm.com
Phone: 91-80-5044999 Fax: 91-80-5268553
T/L : 9243696
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