Messages in this thread | | | Subject | Re: syscall_regfunc() && TIF_SYSCALL_TRACEPOINT | From | Steven Rostedt <> | Date | Sat, 31 Mar 2012 17:37:39 -0400 |
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On Sat, 2012-03-31 at 22:45 +0200, Oleg Nesterov wrote: > On 03/30, Steven Rostedt wrote: > > > > On Fri, 2012-03-30 at 22:15 +0200, Oleg Nesterov wrote: > > > > > But I don't really understand why do you think that "clear" is more > > > important. > > > > They are both important. But as I tend to consider performance when > > tracing is off as critical, I'm more concerned about that. But both must > > be fixed, because not reporting traces can confuse a developer. > > Ah, got it, thanks. > > I was going to send the simple patch we discussed, but suddenly I > realized that I have another question. > > Why do we want to filter out the kernel threads in syscall_regfunc? > > >From cc3b13c1 "tracing: Don't trace kernel thread syscalls" > > then it has no effect to trace the kernel thread calls > to syscalls in that path. > Setting the TIF_SYSCALL_TRACEPOINT flag is then useless for these. > > OK, but then it doesn't hurt? Or is there another reason why > TIF_SYSCALL_TRACEPOINT is not desirable on kthread?
Right, it doesn't hurt. I was about to say that in a previous email.
> > The problem is ____call_usermodehelper() which execs the user-space > task. This clears PF_KTHREAD (sets ->mm), but obviously if > sys_tracepoint_refcount != 0 this is too late. > > So what do you think we should do, > > - keep this check > > - remove it > > - remove it in a separate patch
I say this one (remove it in a separate patch). That way if something breaks we know exactly what did it ;-)
> > - add the "sync with sys_tracepoint_refcount" hook > before kernel_execve() > > ?
-- Steve
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