On Wed, 2011-06-08 at 18:36 +0200, Oleg Nesterov wrote: > On 06/07, Eric Paris wrote: > > > > On Tue, 2011-06-07 at 19:19 +0200, Oleg Nesterov wrote: > > > > > > With or without this patch, can't we call audit_syscall_exit() twice > > > if there is something else in _TIF_WORK_SYSCALL_EXIT mask apart from > > > SYSCALL_AUDIT ? First time it is called from asm, then from > > > syscall_trace_leave(), no? > > > > > > For example. The task has TIF_SYSCALL_AUDIT and nothing else, it does > > > system_call->auditsys->system_call_fastpath. What if it gets, say, > > > TIF_SYSCALL_TRACE before ret_from_sys_call? > > > > No harm is done calling twice. The first call will do the real work and > > cleanup. It will set a flag in the audit data that the work has been > > done (in_syscall == 0) thus the second call will then not do any real > > work and won't have anything to clean up. > > Hmm... and I assume context->previous != NULL is not possible on x86_64. > OK, thanks. > > And I guess, all CONFIG_AUDITSYSCALL code in entry.S is only needed to > microoptimize the case when TIF_SYSCALL_AUDIT is the only reason for the > slow path. I wonder if it really makes the measureble difference... All I know is what Roland put in the changelog: Avoiding the iret return path when syscall audit is enabled helps performance a lot. I believe this was a result of Fedora starting auditd by default and then Linus bitching about how slow a null syscall in a tight loop was. It was an optimization for a microbenchmark. How much it affects things on a real syscall that does real work is probably going to be determined by how much work is done in the syscall. (or just disable auditd in userspace) -Eric
