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SubjectRe: [PATCH v6 4/4] ARM: Add KGDB/KDB FIQ debugger generic code
On 24/06/14 17:22, Nicolas Pitre wrote:
> On Tue, 24 Jun 2014, Daniel Thompson wrote:
>
>> From: Anton Vorontsov <anton.vorontsov@linaro.org>
>>
>> The FIQ debugger may be used to debug situations when the kernel stuck
>> in uninterruptable sections, e.g. the kernel infinitely loops or
>> deadlocked in an interrupt or with interrupts disabled.
>>
>> By default KGDB FIQ is disabled in runtime, but can be enabled with
>> kgdb_fiq.enable=1 kernel command line option.
>>
>> Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
>> Signed-off-by: John Stultz <john.stultz@linaro.org>
>> Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
>> Cc: Russell King <linux@arm.linux.org.uk>
>> Cc: Ben Dooks <ben.dooks@codethink.co.uk>
>> Cc: Dave Martin <Dave.Martin@arm.com>
>> ---
>> arch/arm/Kconfig | 2 +
>> arch/arm/Kconfig.debug | 18 ++++++
>> arch/arm/include/asm/kgdb.h | 7 +++
>> arch/arm/kernel/Makefile | 1 +
>> arch/arm/kernel/kgdb_fiq.c | 124 +++++++++++++++++++++++++++++++++++++++
>> arch/arm/kernel/kgdb_fiq_entry.S | 87 +++++++++++++++++++++++++++
>> 6 files changed, 239 insertions(+)
>> create mode 100644 arch/arm/kernel/kgdb_fiq.c
>> create mode 100644 arch/arm/kernel/kgdb_fiq_entry.S
>
> [...]
>
>> +static long kgdb_fiq_setup_stack(void *info)
>> +{
>> + struct pt_regs regs;
>> +
>> + regs.ARM_sp = __get_free_pages(GFP_KERNEL, THREAD_SIZE_ORDER) +
>> + THREAD_START_SP;
>> + WARN_ON(!regs.ARM_sp);
>
> Isn't this rather fatal if you can't allocate any stack? Why not using
> BUG_ON(), or better yet propagate a proper error code back?

Thanks for raising this.

I think we can get rid of the allocation altogether. This stack is *way*
oversized (it only needs to be 12 bytes).


>> +
>> + set_fiq_regs(&regs);
>> + return 0;
>> +}
>> +
>> +/**
>> + * kgdb_fiq_enable_nmi - Manage NMI-triggered entry to KGDB
>> + * @on: Flag to either enable or disable an NMI
>> + *
>> + * This function manages NMIs that usually cause KGDB to enter. That is, not
>> + * all NMIs should be enabled or disabled, but only those that issue
>> + * kgdb_handle_exception().
>> + *
>> + * The call counts disable requests, and thus allows to nest disables. But
>> + * trying to enable already enabled NMI is an error.
>> + */
>> +static void kgdb_fiq_enable_nmi(bool on)
>> +{
>> + static atomic_t cnt;
>> + int ret;
>> +
>> + ret = atomic_add_return(on ? 1 : -1, &cnt);
>> + if (ret > 1 && on) {
>> + /*
>> + * There should be only one instance that calls this function
>> + * in "enable, disable" order. All other users must call
>> + * disable first, then enable. If not, something is wrong.
>> + */
>> + WARN_ON(1);
>> + return;
>> + }
>
> Minor style suggestion:
>
> /*
> * There should be only one instance that calls this function
> * in "enable, disable" order. All other users must call
> * disable first, then enable. If not, something is wrong.
> */
> if (WARN_ON(ret > 1 && on))
> return;

Will adopt this style.


> Other than that...
>
> Acked-by: Nicolas Pitre <nico@linaro.org>

Thanks for review.



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