linux-kernel - Re: [RFC v5] debug: prevent entering debug mode on panic/exception.

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Date:	Mon, 19 Jan 2015 17:14:55 +0530
From:	Kiran Raparthy <kiran.kumar@...aro.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Colin Cross <ccross@...roid.com>,
	Jason Wessel <jason.wessel@...driver.com>,
	kgdb-bugreport@...ts.sourceforge.net,
	Android Kernel Team <kernel-team@...roid.com>,
	John Stultz <john.stultz@...aro.org>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Kiran Raparthy <kiran.kumar@...aro.org>
Subject: Re: [RFC v5] debug: prevent entering debug mode on panic/exception.

On 13 January 2015 at 15:55, Kiran Raparthy <kiran.kumar@...aro.org> wrote:
> From: Colin Cross <ccross@...roid.com>
>
> debug: prevent entering debug mode on panic/exception.
>
> On non-developer devices, kgdb prevents the device from rebooting
> after a panic.
>
> Incase of panics and exceptions, to allow the device to reboot, prevent entering
> debug mode to avoid getting stuck waiting for the user to interact with debugger.
>
> To avoid entering the debugger on panic/exception without any extra configuration,
> panic_timeout is being used which can be set via /proc/sys/kernel/panic at run time
> and CONFIG_PANIC_TIMEOUT sets the default value.
>
> Setting panic_timeout indicates that the user requested machine to perform
> unattended reboot after panic. We dont want to get stuck waiting for the user
> input incase of panic.
>
> Cc: Jason Wessel <jason.wessel@...driver.com>
> Cc: kgdb-bugreport@...ts.sourceforge.net
> Cc: linux-kernel@...r.kernel.org
> Cc: Android Kernel Team <kernel-team@...roid.com>
> Cc: John Stultz <john.stultz@...aro.org>
> Cc: Sumit Semwal <sumit.semwal@...aro.org>
> Signed-off-by: Colin Cross <ccross@...roid.com>
> [Kiran: Added context to commit message.
> panic_timeout is used instead of break_on_panic and
> break_on_exception to honor CONFIG_PANIC_TIMEOUT
> Modified the commit as per community feedback]
> Signed-off-by: Kiran Raparthy <kiran.kumar@...aro.org>
> Reviewed-by: Daniel Thompson <daniel.thompson@...aro.org>
> ---
>  kernel/debug/debug_core.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
> index 1adf62b..0012a1f 100644
> --- a/kernel/debug/debug_core.c
> +++ b/kernel/debug/debug_core.c
> @@ -689,6 +689,14 @@ kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
>
>         if (arch_kgdb_ops.enable_nmi)
>                 arch_kgdb_ops.enable_nmi(0);
> +       /*
> +        * Avoid entering the debugger if we were triggered due to an oops
> +        * but panic_timeout indicates the system should automatically
> +        * reboot on panic. We don't want to get stuck waiting for input
> +        * on such systems, especially if its "just" an oops.
> +        */
> +       if (signo != SIGTRAP && panic_timeout)
> +               return 1;
>
>         memset(ks, 0, sizeof(struct kgdb_state));
>         ks->cpu                 = raw_smp_processor_id();
> @@ -821,6 +829,15 @@ static int kgdb_panic_event(struct notifier_block *self,
>                             unsigned long val,
>                             void *data)
>  {
> +       /*
> +        * Avoid entering the debugger if we were triggered due to a panic
> +        * We don't want to get stuck waiting for input from user in such case.
> +        * panic_timeout indicates the system should automatically
> +        * reboot on panic.
> +        */
> +       if (panic_timeout)
> +               return NOTIFY_DONE;
> +
>         if (dbg_kdb_mode)
>                 kdb_printf("PANIC: %s\n", (char *)data);
>         kgdb_breakpoint();
> --
> 1.8.2.1
>
Gentle reminder.
Regards,
Kiran
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