On Tue, Jul 29, 2014 at 09:32:32PM +0200, Oleg Nesterov wrote:
> On 07/28, Andy Lutomirski wrote:
> >
> > @@ -1449,7 +1449,12 @@ long syscall_trace_enter(struct pt_regs *regs)
> > {
> > long ret = 0;
> >
> > - user_exit();
> > + /*
> > + * If TIF_NOHZ is set, we are required to call user_exit() before
> > + * doing anything that could touch RCU.
> > + */
> > + if (test_thread_flag(TIF_NOHZ))
> > + user_exit();
>
> Personally I still think this change just adds more confusion, but I leave
> this to you and Frederic.
>
> It is not that "If TIF_NOHZ is set, we are required to call user_exit()", we
> need to call user_exit() just because we enter the kernel. TIF_NOHZ is just
> the implementation detail which triggers this slow path.
>
> At least it should be correct, unless I am confused even more than I think.
Agreed, Perhaps the confusion is on the syscall_trace_enter() name which suggests
this is only about tracing? syscall_slowpath_enter() could be an alternative.
But that's still tracing in a general sense so...
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