unfuck proc_sysctl ->d_compare()
a) struct inode is not going to be freed under ->d_compare();
however, the thing PROC_I(inode)->sysctl points to just might.
Fortunately, it's enough to make freeing that sucker delayed,
provided that we don't step on its ->unregistering, clear
the pointer to it in PROC_I(inode) before dropping the reference
and check if it's NULL in ->d_compare().
b) I'm not sure that we *can* walk into NULL inode here (we recheck
dentry->seq between verifying that it's still hashed / fetching
dentry->d_inode and passing it to ->d_compare() and there's no
negative hashed dentries in /proc/sys/*), but if we can walk into
that, we really should not have ->d_compare() return 0 on it!
Said that, I really suspect that this check can be simply killed.
Nick?
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 7bb5cb6..bb7c2b0 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -25,6 +25,7 @@
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/compiler.h>
+#include <linux/rcupdate.h>
struct completion;
@@ -1037,10 +1038,15 @@
struct ctl_table trees. */
struct ctl_table_header
{
- struct ctl_table *ctl_table;
- struct list_head ctl_entry;
- int used;
- int count;
+ union {
+ struct {
+ struct ctl_table *ctl_table;
+ struct list_head ctl_entry;
+ int used;
+ int count;
+ };
+ struct rcu_head rcu;
+ };
struct completion *unregistering;
struct ctl_table *ctl_table_arg;
struct ctl_table_root *root;