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

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Date:	Wed, 28 Jan 2015 16:45:04 +0530
From:	Kiran Raparthy <kiran.kumar@...aro.org>
To:	Daniel Thompson <daniel.thompson@...aro.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	kgdb-bugreport@...ts.sourceforge.net,
	Colin Cross <ccross@...roid.com>,
	John Stultz <john.stultz@...aro.org>,
	Jason Wessel <jason.wessel@...driver.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Sumit Semwal <sumit.semwal@...aro.org>
Subject: Re: [Kgdb-bugreport] [RFC v5 - RESEND] debug: prevent entering debug
 mode on panic/exception.

On 28 January 2015 at 16:25, Daniel Thompson <daniel.thompson@...aro.org> wrote:
> On 28/01/15 10:39, Kiran Raparthy 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.
>
> Some kind of changelog between the versions would have been nice. I
> *think* the difference between v4 and v5 was just the addition paragraph
> above but I had to put in extra work to check that and I'm still not
> 100% sure that's the only change.
Since the change was related to only commit message on all the earlier
patches,i didn't update the history.
Anyways i'll ensure to include the history going forward.
>
> Also you could start billing this as a PATCH rather than an RFC.
Since i didn't get any acknowledgement,i didn't upgrade it to PATCH.
Anyways,i'll update and resend the patch,Thanks for the inputs.

>
>
> Daniel.
>
>
>> Cc: Jason Wessel <jason.wessel@...driver.com>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> 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();
>>
>

Regards,
Kiran
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