On Wed, Mar 29, 2017 at 9:33 AM, Oleg Nesterov <o...@redhat.com> 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