linux-kernel - Re: [PATCH] mm: Always print RLIMIT

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Message-ID: <CALYGNiOUZXiOeWSYMgeF3792NNWAgpcxnAOMQ_Wb-d1-Xo_k0Q@mail.gmail.com>
Date:   Tue, 6 Feb 2018 20:48:46 +0300
From:   Konstantin Khlebnikov <koct9i@...il.com>
To:     David Woodhouse <dwmw@...zon.co.uk>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Vladimir Davydov <vdavydov@...tuozzo.com>,
        Andy Lutomirski <luto@...capital.net>,
        Quentin Casasnovas <quentin.casasnovas@...cle.com>,
        Kees Cook <keescook@...gle.com>, Willy Tarreau <w@....eu>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Laura Abbott <labbott@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org
Subject: Re: [PATCH] mm: Always print RLIMIT_DATA warning

On Tue, Feb 6, 2018 at 7:45 PM, David Woodhouse <dwmw@...zon.co.uk> wrote:
> The documentation for ignore_rlimit_data says that it will print a warning
> at first misuse. Yet it doesn't seem to do that. Fix the code to print
> the warning even when we allow the process to continue.

Ack. But I think this was a misprint in docs.
Anyway, this knob is a kludge so we might warn once even if it is set.

So, somebody still have problems with this change?
I remember concerns about that "warn_once" isn't enough to detect
what's going wrong.
And probably we should invent  "warn_sometimes".

>
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> ---
> We should probably also do what Linus suggested in
> https://lkml.org/lkml/2016/9/16/585
>
>  mm/mmap.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 9efdc021..dd76ea3 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -3184,13 +3184,15 @@ bool may_expand_vm(struct mm_struct *mm, vm_flags_t flags, unsigned long npages)
>                 if (rlimit(RLIMIT_DATA) == 0 &&
>                     mm->data_vm + npages <= rlimit_max(RLIMIT_DATA) >> PAGE_SHIFT)
>                         return true;
> -               if (!ignore_rlimit_data) {
> -                       pr_warn_once("%s (%d): VmData %lu exceed data ulimit %lu. Update limits or use boot option ignore_rlimit_data.\n",
> -                                    current->comm, current->pid,
> -                                    (mm->data_vm + npages) << PAGE_SHIFT,
> -                                    rlimit(RLIMIT_DATA));
> +
> +               pr_warn_once("%s (%d): VmData %lu exceed data ulimit %lu. Update limits%s.\n",
> +                            current->comm, current->pid,
> +                            (mm->data_vm + npages) << PAGE_SHIFT,
> +                            rlimit(RLIMIT_DATA),
> +                            ignore_rlimit_data ? "" : " or use boot option ignore_rlimit_data");
> +
> +               if (!ignore_rlimit_data)
>                         return false;
> -               }
>         }
>
>         return true;
> --
> 2.7.4
>