On Wed, 2011-06-08 at 18:36 +0200, Oleg Nesterov wrote:
On 06/07, Eric Paris wrote:
quoted
On Tue, 2011-06-07 at 19:19 +0200, Oleg Nesterov wrote:
quoted
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
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