Re: [PATCH] audit: speedup for syscalls when auditing is disabled

[Anton Blanchard <anton@samba.org>]

Hi Eric,

Here's another approach Mikey and I were discussing. We allocate the
tsk->audit_context as before, but we avoid setting the TIF_SYSCALL_AUDIT until
the first rule gets added.

We could look at clearing the flag when the rules go back to zero, but this
simple patch covers the most common case I think.

Anton
---

Index: powerpc.git/kernel/auditfilter.c
===================================================================
--- powerpc.git.orig/kernel/auditfilter.c	2010-08-26 08:04:19.998892577 +1000
+++ powerpc.git/kernel/auditfilter.c	2010-08-26 08:04:30.290374256 +1000
@@ -859,6 +859,21 @@ out:
 static u64 prio_low = ~0ULL/2;
 static u64 prio_high = ~0ULL/2 - 1;
 
+#ifdef CONFIG_AUDITSYSCALL
+static void enable_syscall_auditing(void)
+{
+	unsigned long flags;
+	struct task_struct *g, *t;
+
+	read_lock_irqsave(&tasklist_lock, flags);
+	do_each_thread(g, t) {
+		if (t->audit_context)
+			set_tsk_thread_flag(t, TIF_SYSCALL_AUDIT);
+	} while_each_thread(g, t);
+	read_unlock_irqrestore(&tasklist_lock, flags);
+}
+#endif
+
 /* Add rule to given filterlist if not a duplicate. */
 static inline int audit_add_rule(struct audit_entry *entry)
 {
@@ -922,9 +937,14 @@ static inline int audit_add_rule(struct
 		list_add_tail_rcu(&entry->list, list);
 	}
 #ifdef CONFIG_AUDITSYSCALL
-	if (!dont_count)
+	if (!dont_count) {
 		audit_n_rules++;
 
+		/* Did we add our first rule? */
+		if (audit_n_rules == 1)
+			enable_syscall_auditing();
+	}
+
 	if (!audit_match_signal(entry))
 		audit_signals++;
 #endif
Index: powerpc.git/kernel/auditsc.c
===================================================================
--- powerpc.git.orig/kernel/auditsc.c	2010-08-26 08:04:19.998892577 +1000
+++ powerpc.git/kernel/auditsc.c	2010-08-26 08:04:30.390388654 +1000
@@ -886,7 +886,10 @@ int audit_alloc(struct task_struct *tsk)
 	context->filterkey = key;
 
 	tsk->audit_context  = context;
-	set_tsk_thread_flag(tsk, TIF_SYSCALL_AUDIT);
+
+	/* We postpone setting the thread flag until we add the first rule */
+	if (audit_n_rules != 0)
+		set_tsk_thread_flag(tsk, TIF_SYSCALL_AUDIT);
 	return 0;
 }