AUDIT: Reduce contention in audit_serial()

... by generating serial numbers only if an audit context is actually
_used_, rather than doing so at syscall entry even when the context
isn't necessarily marked auditable.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>

diff --git a/kernel/audit.c b/kernel/audit.c
index 27ffcf3..d321e25 100644 (file)
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -625,7 +625,9 @@ unsigned int audit_serial(void)
        unsigned int ret;
 
        spin_lock_irqsave(&serial_lock, flags);
-       ret = serial++;
+       do {
+               ret = ++serial;
+       } while (unlikely(!ret));
        spin_unlock_irqrestore(&serial_lock, flags);
 
        return ret;

diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 242d45e..46b45ab 100644 (file)
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -984,7 +984,7 @@ void audit_syscall_entry(struct task_struct *tsk, int arch, int major,
        if (likely(state == AUDIT_DISABLED))
                return;
 
-       context->serial     = audit_serial();
+       context->serial     = 0;
        context->ctime      = CURRENT_TIME;
        context->in_syscall = 1;
        context->auditable  = !!(state == AUDIT_RECORD_CONTEXT);
@@ -1138,6 +1138,8 @@ void audit_inode(const char *name, const struct inode *inode, unsigned flags)
 void auditsc_get_stamp(struct audit_context *ctx,
                       struct timespec *t, unsigned int *serial)
 {
+       if (!ctx->serial)
+               ctx->serial = audit_serial();
        t->tv_sec  = ctx->ctime.tv_sec;
        t->tv_nsec = ctx->ctime.tv_nsec;
        *serial    = ctx->serial;