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>

1 files changed, 3 insertions, 1 deletions

diff --git a/kernel/audit.c b/kernel/audit.c
index 27ffcf363f8d..d321e251d32b 100644
--- 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;