From: Stephen Smalley <sds@epoch.ncsc.mil>

This patch fixes a bug in the SELinux access vector cache code, which was
incorrectly using spin_lock_irq rather than spin_lock_irqsave for the
avc_log_lock.  As this code can be called from hardirq (e.g.  from the
file_send_sigiotask hook), we need irqsave/restore here.