[PATCH] Keys: Use RCU to manage session keyring pointer

The attached patch uses RCU to manage the session keyring pointer in struct
signal_struct.  This means that searching need not disable interrupts and get
a the sighand spinlock to access this pointer.  Furthermore, by judicious use
of rcu_read_(un)lock(), this patch also avoids the need to take and put
refcounts on the session keyring itself, thus saving on even more atomic ops.

Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 4 deletions

diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 1919540f047d..54aa7b70e63b 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -175,13 +175,12 @@ static struct key *__request_key_construction(struct key_type *type,
         key->expiry = now.tv_sec + key_negative_timeout;
 
         if (current->signal->session_keyring) {
-                unsigned long flags;
                 struct key *keyring;
 
-                spin_lock_irqsave(&current->sighand->siglock, flags);
-                keyring = current->signal->session_keyring;
+                rcu_read_lock();
+                keyring = rcu_dereference(current->signal->session_keyring);
                 atomic_inc(&keyring->usage);
-                spin_unlock_irqrestore(&current->sighand->siglock, flags);
+                rcu_read_unlock();
 
                 key_link(keyring, key);
                 key_put(keyring);