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Date:   Mon, 28 Jan 2019 10:05:45 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Vincent Whitchurch <vincent.whitchurch@axis.com>
Cc:     mcgrof@kernel.org, keescook@chromium.org,
        linux-kernel@vger.kernel.org, Vincent Whitchurch <rabinv@axis.com>
Subject: Re: [PATCH v2] sysctl: Add panic-fatal-signals
Message-Id: <20190128100545.b62193aa8f49e1de8d6ea8b7@linux-foundation.org>
In-Reply-To: <20190128084959.13060-1-vincent.whitchurch@axis.com>
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On Mon, 28 Jan 2019 09:49:59 +0100 Vincent Whitchurch <vincent.whitchurch@axis.com> wrote:

> Add a sysctl which asks the kernel to panic when any userspace process
> receives a fatal signal which would trigger a core dump.  This has
> proven to be quite useful when debugging problems seen during testing of
> embedded systems:  When combined with kernel core dumps (saved due to
> the panic), it allows easier debugging of crashes which have their
> origin in system-wide problems such as buggy drivers or other kernel or
> hardware-related issues.
> 
> The crashing process's core dump can be extracted from the kernel core
> dump using tools such as the crash utility's gcore extension.
> 

I can't speak to the usefulness of this, but the feature is small and
simple.

Some documentation would be appreciated.  I assume in
Documentation/sysctl/kernel.txt.  Please also check that
print-fatal-signals is appropriately documented while we're in there -
it's documented in Documentation/admin-guide/kernel-parameters.rst but
not Documentation/sysctl/kernel.txt.

> v2: Put the sysctl behind a config option

I suppose so...  The option is root-only (surely?) so I'm not sure this
is really needed.

> ...
>
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1242,6 +1242,20 @@ config SYSCTL_SYSCALL
>  
>  	  If unsure say N here.
>  
> +config SYSCTL_PANIC_FATAL_SIGNALS
> +	bool "panic-fatal-signals sysctl" if EXPERT
> +	depends on PROC_SYSCTL
> +	help
> +	  If you say Y here, a kernel.panic-fatal-signals sysctl will be
> +	  offered.  If this sysctl is turned on, the kernel will panic if any
> +	  userspace process receives a fatal signal which would trigger a core
> +	  dump.
> +
> +	  When used together with kernel core dumps, this can be useful for
> +	  debugging some system-wide problems, primarily on embedded systems.
> +
> +	  If unsure, say N.

I suggest that the Kconfig help and the forthcoming documentation
should clearly explain the dangers of enabling this!