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authorAl Viro <viro@zeniv.linux.org.uk>2011-03-08 01:25:28 -0500
committerAl Viro <viro@zeniv.linux.org.uk>2011-03-08 02:22:27 -0500
commitdfef6dcd35cb4a251f6322ca9b2c06f0bb1aa1f4 (patch)
tree65e8a25d4ed913658db35c4b97ab0a021c2124eb
parent1858efd471624ecb37e6b5462cab8076f47d1cee (diff)
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>
-rw-r--r--fs/proc/inode.c8
-rw-r--r--fs/proc/proc_sysctl.c7
-rw-r--r--include/linux/sysctl.h14
-rw-r--r--kernel/sysctl.c15
4 files changed, 31 insertions, 13 deletions
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 176ce4cda68a..d6a7ca1fdac5 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -27,6 +27,7 @@
static void proc_evict_inode(struct inode *inode)
{
struct proc_dir_entry *de;
+ struct ctl_table_header *head;
truncate_inode_pages(&inode->i_data, 0);
end_writeback(inode);
@@ -38,8 +39,11 @@ static void proc_evict_inode(struct inode *inode)
de = PROC_I(inode)->pde;
if (de)
pde_put(de);
- if (PROC_I(inode)->sysctl)
- sysctl_head_put(PROC_I(inode)->sysctl);
+ head = PROC_I(inode)->sysctl;
+ if (head) {
+ rcu_assign_pointer(PROC_I(inode)->sysctl, NULL);
+ sysctl_head_put(head);
+ }
}
struct vfsmount *proc_mnt;
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 09a1f92a34ef..8eb2522111c5 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -408,15 +408,18 @@ static int proc_sys_compare(const struct dentry *parent,
const struct dentry *dentry, const struct inode *inode,
unsigned int len, const char *str, const struct qstr *name)
{
+ struct ctl_table_header *head;
/* Although proc doesn't have negative dentries, rcu-walk means
* that inode here can be NULL */
+ /* AV: can it, indeed? */
if (!inode)
- return 0;
+ return 1;
if (name->len != len)
return 1;
if (memcmp(name->name, str, len))
return 1;
- return !sysctl_is_seen(PROC_I(inode)->sysctl);
+ head = rcu_dereference(PROC_I(inode)->sysctl);
+ return !head || !sysctl_is_seen(head);
}
static const struct dentry_operations proc_sys_dentry_operations = {
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 7bb5cb64f3b8..bb7c2b086fa4 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_root {
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;
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 0f1bd83db985..4eed0af5d144 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -194,9 +194,9 @@ static int sysrq_sysctl_handler(ctl_table *table, int write,
static struct ctl_table root_table[];
static struct ctl_table_root sysctl_table_root;
static struct ctl_table_header root_table_header = {
- .count = 1,
+ {{.count = 1,
.ctl_table = root_table,
- .ctl_entry = LIST_HEAD_INIT(sysctl_table_root.default_set.list),
+ .ctl_entry = LIST_HEAD_INIT(sysctl_table_root.default_set.list),}},
.root = &sysctl_table_root,
.set = &sysctl_table_root.default_set,
};
@@ -1567,11 +1567,16 @@ void sysctl_head_get(struct ctl_table_header *head)
spin_unlock(&sysctl_lock);
}
+static void free_head(struct rcu_head *rcu)
+{
+ kfree(container_of(rcu, struct ctl_table_header, rcu));
+}
+
void sysctl_head_put(struct ctl_table_header *head)
{
spin_lock(&sysctl_lock);
if (!--head->count)
- kfree(head);
+ call_rcu(&head->rcu, free_head);
spin_unlock(&sysctl_lock);
}
@@ -1948,10 +1953,10 @@ void unregister_sysctl_table(struct ctl_table_header * header)
start_unregistering(header);
if (!--header->parent->count) {
WARN_ON(1);
- kfree(header->parent);
+ call_rcu(&header->parent->rcu, free_head);
}
if (!--header->count)
- kfree(header);
+ call_rcu(&header->rcu, free_head);
spin_unlock(&sysctl_lock);
}