is_subdir-fix
PATCH 1/1 is_subdir-fix
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(+)
fs/dcache.c renamed from fs/dcache.c~is_subdir-fix +9 -0
@@ -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_dentrybreak ; } }while (read_seqretry (&rename_lock, seq)); +rcu_read_unlock ();return result; }
_
Signature · 6 lines
Maneesh Soni Linux Technology Center, IBM Software Lab, Bangalore, India email: [email protected] Phone: 91-80-5044999 Fax: 91-80-5268553 T/L : 9243696