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Date: Wed, 29 Mar 2017 09:45:12 -0700 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Oleg Nesterov <oleg@...hat.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Andy Lutomirski <luto@...nel.org>, Denys Vlasenko <dvlasenk@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, Jan Kratochvil <jan.kratochvil@...hat.com>, Pedro Alves <palves@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, "the arch/x86 maintainers" <x86@...nel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: syscall_get_error() && TS_ checks On Wed, Mar 29, 2017 at 9:33 AM, Oleg Nesterov <oleg@...hat.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
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