@@ -56,10 +56,19 @@ static void configfs_d_iput(struct dentry * dentry,
struct configfs_dirent *sd = dentry->d_fsdata;
if (sd) {
- BUG_ON(sd->s_dentry != dentry);
/* Coordinate with configfs_readdir */
spin_lock(&configfs_dirent_lock);
- sd->s_dentry = NULL;
+ /* Coordinate with configfs_attach_attr where will increase
+ * sd->s_count and update sd->s_dentry to new allocated one.
+ * Only set sd->dentry to null when this dentry is the only
+ * sd owner.
+ * If not do so, configfs_d_iput may run just after
+ * configfs_attach_attr and set sd->s_dentry to null
+ * even it's still in use.
+ */
+ if (atomic_read(&sd->s_count) <= 2)
+ sd->s_dentry = NULL;
+
spin_unlock(&configfs_dirent_lock);
configfs_put(sd);
}
@@ -426,8 +435,11 @@ static int configfs_attach_attr(struct configfs_dirent * sd, struct dentry * den
struct configfs_attribute * attr = sd->s_element;
int error;
+ spin_lock(&configfs_dirent_lock);
dentry->d_fsdata = configfs_get(sd);
sd->s_dentry = dentry;
+ spin_unlock(&configfs_dirent_lock);
+
error = configfs_create(dentry, (attr->ca_mode & S_IALLUGO) | S_IFREG,
configfs_init_file);
if (error) {
A race window in configfs, it starts from one dentry is UNHASHED and end before configfs_d_iput is called. In this window, if a lookup happen, since the original dentry was UNHASHED, so a new dentry will be allocated, and then in configfs_attach_attr(), sd->s_dentry will be updated to the new dentry. Then in configfs_d_iput(), BUG_ON(sd->s_dentry != dentry) will be triggered and system panic. sys_open: sys_close: ... fput dput dentry_kill __d_drop <--- dentry unhashed here, but sd->dentry still point to this dentry. lookup_real configfs_lookup configfs_attach_attr---> update sd->s_dentry to new allocated dentry here. d_kill configfs_d_iput <--- BUG_ON(sd->s_dentry != dentry) triggered here. For fix it, change configfs_d_iput to not update sd->s_dentry if sd->s_count > 2, that means there are another dentry is using the sd beside the one that is going to be put. Use configfs_dirent_lock in configfs_attach_attr to sync with configfs_d_iput. With the following steps, you can reproduce the bug. 1. enable ocfs2, this will mount configfs at /sys/kernel/config and fill configure in it. 2. run the following script. while [ 1 ]; do cat /sys/kernel/config/cluster/$your_cluster_name/idle_timeout_ms > /dev/null; done & while [ 1 ]; do cat /sys/kernel/config/cluster/$your_cluster_name/idle_timeout_ms > /dev/null; done & Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com> Cc: stable@vger.kernel.org Cc: Joel Becker <jlbec@evilplan.org> Cc: Andrew Morton <akpm@linux-foundation.org> --- fs/configfs/dir.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-)