Re: syscall_get_error() && TS_ checks

[Linus Torvalds]

On Wed, Mar 29, 2017 at 9:33 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>
> Firstly, why do we need the IS_ERR_VALUE() check? This is only used by
> do_signal/handle_signal, we do not care if it returns non-zero as long
> as the value can't be confused with -ERESTART.* codes.

There are system calls that can return "negative" values that aren't errors.

Notably mmap() can return a valid pointer with the high bit set.

So syscall_get_error() should return 0 for not just positive return
values, but for those kinds of negative non-error values.

> And why do we need the TS_ checks?

Those may be bogus.

> So why we can't simply change putreg32() to always sign-extend regs->ax
> regs->orig_ax and just do
>
>         static inline long syscall_get_error(struct task_struct *task,
>                                              struct pt_regs *regs)
>         {
>                 return regs-ax;
>         }

That would be *complete* garbage. Lots of system calls return positive
values that sure as hell aren't errors.

                    Linus