[PATCH] audit: use pid.is_auditd to make auditd_test_task() faster

[Eiichi Tsukata]

auditd_test_task() is a hot path of system call auditing. This patch
introduces a new bit field "is_auditd" in pid struct which can be used
for faster check of registered audit daemon.

Benchmark
=========

Run the following command:

  dd if=/dev/zero of=/dev/null bs=1 count=5M

With rule:

  -a never,exit -F arch=b64 -S uname

Result:

  Base line    : 2.572 sec
  /w this patch: 2.412 sec (6.6% faster)

Signed-off-by: Eiichi Tsukata <eiichi.tsukata@xxxxxxxxxxx>
---
 include/linux/pid.h |  4 ++++
 kernel/audit.c      | 22 ++--------------------
 kernel/audit.h      |  3 ++-
 kernel/pid.c        |  3 +++
 4 files changed, 11 insertions(+), 21 deletions(-)

diff --git a/include/linux/pid.h b/include/linux/pid.h
index 343abf22092e..5fe38e254c9a 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -68,6 +68,10 @@ struct pid
 	wait_queue_head_t wait_pidfd;
 	struct rcu_head rcu;
 	struct upid numbers[1];
+#ifdef CONFIG_AUDIT
+	/* registered audit daemon tgid */
+	unsigned is_auditd:1;
+#endif
 };
 
 extern struct pid init_struct_pid;
diff --git a/kernel/audit.c b/kernel/audit.c
index 9bc0b0301198..964d1a20c32d 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -208,26 +208,6 @@ struct audit_reply {
 	struct sk_buff *skb;
 };
 
-/**
- * auditd_test_task - Check to see if a given task is an audit daemon
- * @task: the task to check
- *
- * Description:
- * Return 1 if the task is a registered audit daemon, 0 otherwise.
- */
-int auditd_test_task(struct task_struct *task)
-{
-	int rc;
-	struct auditd_connection *ac;
-
-	rcu_read_lock();
-	ac = rcu_dereference(auditd_conn);
-	rc = (ac && ac->pid == task_tgid(task) ? 1 : 0);
-	rcu_read_unlock();
-
-	return rc;
-}
-
 /**
  * audit_ctl_lock - Take the audit control lock
  */
@@ -478,6 +458,7 @@ static void auditd_conn_free(struct rcu_head *rcu)
 	struct auditd_connection *ac;
 
 	ac = container_of(rcu, struct auditd_connection, rcu);
+	ac->pid->is_auditd = 0;
 	put_pid(ac->pid);
 	put_net(ac->net);
 	kfree(ac);
@@ -505,6 +486,7 @@ static int auditd_set(struct pid *pid, u32 portid, struct net *net)
 	if (!ac_new)
 		return -ENOMEM;
 	ac_new->pid = get_pid(pid);
+	ac_new->pid->is_auditd = 1;
 	ac_new->portid = portid;
 	ac_new->net = get_net(net);
 
diff --git a/kernel/audit.h b/kernel/audit.h
index c57b008b9914..aecf334a699f 100644
--- a/kernel/audit.h
+++ b/kernel/audit.h
@@ -214,7 +214,8 @@ extern bool audit_ever_enabled;
 
 extern void audit_log_session_info(struct audit_buffer *ab);
 
-extern int auditd_test_task(struct task_struct *task);
+/* Check to see if a given task is an audit daemon */
+#define auditd_test_task(tsk) task_tgid(tsk)->is_auditd
 
 #define AUDIT_INODE_BUCKETS	32
 extern struct list_head audit_inode_hash[AUDIT_INODE_BUCKETS];
diff --git a/kernel/pid.c b/kernel/pid.c
index 3fbc5e46b721..c0efaeee99a0 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -183,6 +183,9 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
 
 	tmp = ns;
 	pid->level = ns->level;
+#ifdef CONFIG_AUDIT
+	pid->is_auditd = 0;
+#endif
 
 	for (i = ns->level; i >= 0; i--) {
 		int tid = 0;
-- 
2.39.2