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?

Al Viro committed 15 years ago

Commit dfef6dc1 parent 1858efd4 files · +31 −13Browse files

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include/linux/sysctl.h+10−4

@@ -25,6 +25,7 @@ · 24 unmodified lines
25	25	#include <linux/kernel.h>
26	26	#include <linux/types.h>
27	27	#include <linux/compiler.h>
	28	+#include <linux/rcupdate.h>
28	29
29	30	struct completion;
30	31
@@ -1037,10 +1038,15 @@ struct ctl_table_root { · 1006 unmodified lines
1037	1038	struct ctl_table trees. */
1038	1039	struct ctl_table_header
1039	1040	{
1040		− struct ctl_table *ctl_table;
1041		− struct list_head ctl_entry;
1042		− int used;
1043		− int count;
	1041	+ union {
	1042	+ struct {
	1043	+ struct ctl_table *ctl_table;
	1044	+ struct list_head ctl_entry;
	1045	+ int used;
	1046	+ int count;
	1047	+ };
	1048	+ struct rcu_head rcu;
	1049	+ };
1044	1050	struct completion *unregistering;
1045	1051	struct ctl_table *ctl_table_arg;
1046	1052	struct ctl_table_root *root;