linux-kernel - Re: [PATCH] ARM: mm: Facilitate debugging CONFIG_KUSER

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Message-ID: <CAFqt6zYxY+ocQPwNnV3CE7pTrUFniQETcxsq4Dsof41E91L6BQ@mail.gmail.com>
Date:   Fri, 26 Oct 2018 00:00:09 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org, Andrew Lunn <andrew@...n.ch>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        ebiederm@...ssion.com, Tony Lindgren <tony@...mide.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: mm: Facilitate debugging CONFIG_KUSER_HELPERS disabled

On Thu, Oct 25, 2018 at 11:40 PM Florian Fainelli <f.fainelli@...il.com> wrote:
>
> Some software such as perf makes unconditional use of the special
> [vectors] page which is only provided when CONFIG_KUSER_HELPERS is
> enabled in the kernel.
>
> Facilitate the debugging of such situations by printing a debug message
> to the kernel log showing the task name and the faulting address.
>
> Suggested-by: Russell King <rmk+kernel@...linux.org.uk>
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
>  arch/arm/mm/fault.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
> index f4ea4c62c613..f17471fbc1c4 100644
> --- a/arch/arm/mm/fault.c
> +++ b/arch/arm/mm/fault.c
> @@ -173,6 +173,11 @@ __do_user_fault(struct task_struct *tsk, unsigned long addr,
>                 show_regs(regs);
>         }
>  #endif
> +#ifndef CONFIG_KUSER_HELPERS

Just have one doubt, if the condition is "#ifdef CONFIG_KUSER_HELPER"
as commit message suggests the scenario is valid when CONFIG_KUSER_HELPER
is enabled ? No ?

> +       if ((sig == SIGSEGV) && ((addr & PAGE_MASK) == 0xffff0000))
> +               printk(KERN_DEBUG "%s: CONFIG_KUSER_HELPERS disabled at 0x%08lx\n",
> +                      tsk->comm, addr);
> +#endif
>
>         tsk->thread.address = addr;
>         tsk->thread.error_code = fsr;
> --
> 2.17.1
>