linux-kernel - Re: Linux 4.12-rc6

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Date:   Tue, 20 Jun 2017 10:11:36 +0100
From:   Andy Whitcroft <apw@...onical.com>
To:     Dave Jones <davej@...emonkey.org.uk>,
        Hugh Dickins <hughd@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>, Michal Hocko <mhocko@...e.com>
Subject: Re: Linux 4.12-rc6

On Tue, Jun 20, 2017 at 4:42 AM, Dave Jones <davej@...emonkey.org.uk> wrote:

> Almost shutdown, but not quite.  Coincidentally, coverity just finished
> the rc6 run, and barfed this up..  related ?
>
> *** CID 1412907:  Control flow issues  (DEADCODE)
> /include/linux/mm.h: 2243 in vm_end_gap()
> 2237
> 2238     static inline unsigned long vm_end_gap(struct vm_area_struct *vma)
> 2239     {
> 2240            unsigned long vm_end = vma->vm_end;
> 2241
> 2242            if (vma->vm_flags & VM_GROWSUP) {
>>>>     CID 1412907:  Control flow issues  (DEADCODE)
>>>>     Execution cannot reach this statement: "vm_end += stack_guard_gap;".
> 2243                    vm_end += stack_guard_gap;
> 2244                    if (vm_end < vma->vm_end)
> 2245                            vm_end = -PAGE_SIZE;
> 2246            }
> 2247            return vm_end;
> 2248     }

I suspect this is because coverity can tell we do not use VM_GROWSUP
in x86.  I assume it would say the corresponding thing about the
VM_GROWSDOWN code in vm_start_gap() on those architectures with upward
growing stacks.

-apw