Re: [PATCH 7/7] kgdb: Remove irq flags and local_irq_enable/disable from roundup

Daniel Thompson
2018-10-30T11:46:03Z

On Mon, Oct 29, 2018 at 11:07:07AM -0700, Douglas Anderson wrote:
> The function kgdb_roundup_cpus() was passed a parameter that was
> documented as:
>
> > the flags that will be used when restoring the interrupts. There is
> > local_irq_save() call before kgdb_roundup_cpus().
>
> Nobody used those flags. Anyone who wanted to temporarily turn on
> interrupts just did local_irq_enable() and local_irq_disable() without
> looking at them. So we can definitely remove the flags.

On the whole I'd rather that this change...

> Speaking of calling local_irq_enable(), it seems like a bad idea and
> it caused a nice splat on my system with lockdep turned on.
> Specifically it hit:
> DEBUG_LOCKS_WARN_ON(current->hardirq_context)

... and fixes for this this were in separate patches. They don't appear
especially related.

Daniel.

> See the previous patch in this series ("smp: Don't yell about IRQs
> disabled in kgdb_roundup_cpus()") for more details, but the last few
> things on the stack were this on my arm64 board:
> lockdep_hardirqs_on+0xf0/0x160
> trace_hardirqs_on+0x188/0x1ac
> kgdb_roundup_cpus+0x14/0x3c
>
> As agrued in the the commit text of ("smp: Don't yell about IRQs
> disabled in kgdb_roundup_cpus()"), it seems better to make
> smp_call_function() lenient about kgdb than to locally turn on IRQs
> here. Thus let's totally remove all the local_irq_enable() and
> local_irq_disable() calls from all of the kgdb_roundup_cpus() calls.
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
>
> arch/arc/kernel/kgdb.c | 4 +---
> arch/arm/kernel/kgdb.c | 4 +---
> arch/arm64/kernel/kgdb.c | 4 +---
> arch/hexagon/kernel/kgdb.c | 11 ++---------
> arch/mips/kernel/kgdb.c | 4 +---
> arch/powerpc/kernel/kgdb.c | 2 +-
> arch/sh/kernel/kgdb.c | 4 +---
> arch/sparc/kernel/smp_64.c | 2 +-
> arch/x86/kernel/kgdb.c | 9 ++-------
> include/linux/kgdb.h | 9 ++-------
> kernel/debug/debug_core.c | 2 +-
> 11 files changed, 14 insertions(+), 41 deletions(-)
>
> diff --git a/arch/arc/kernel/kgdb.c b/arch/arc/kernel/kgdb.c
> index 9a3c34af2ae8..d94d3cb7f9e8 100644
> --- a/arch/arc/kernel/kgdb.c
> +++ b/arch/arc/kernel/kgdb.c
> @@ -197,11 +197,9 @@ static void kgdb_call_nmi_hook(void *ignored)
> kgdb_nmicallback(raw_smp_processor_id(), NULL);
> }
>
> -void kgdb_roundup_cpus(unsigned long flags)
> +void kgdb_roundup_cpus(void)
> {
> - local_irq_enable();
> smp_call_function(kgdb_call_nmi_hook, NULL, 0);
> - local_irq_disable();
> }
>
> struct kgdb_arch arch_kgdb_ops = {
> diff --git a/arch/arm/kernel/kgdb.c b/arch/arm/kernel/kgdb.c
> index caa0dbe3dc61..a80e9259f7e9 100644
> --- a/arch/arm/kernel/kgdb.c
> +++ b/arch/arm/kernel/kgdb.c
> @@ -175,11 +175,9 @@ static void kgdb_call_nmi_hook(void *ignored)
> kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
> }
>
> -void kgdb_roundup_cpus(unsigned long flags)
> +void kgdb_roundup_cpus(void)
> {
> - local_irq_enable();
> smp_call_function(kgdb_call_nmi_hook, NULL, 0);
> - local_irq_disable();
> }
>
> static int __kgdb_notify(struct die_args *args, unsigned long cmd)
> diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c
> index a20de58061a8..5d171c26788f 100644
> --- a/arch/arm64/kernel/kgdb.c
> +++ b/arch/arm64/kernel/kgdb.c
> @@ -289,11 +289,9 @@ static void kgdb_call_nmi_hook(void *ignored)
> kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
> }
>
> -void kgdb_roundup_cpus(unsigned long flags)
> +void kgdb_roundup_cpus(void)
> {
> - local_irq_enable();
> smp_call_function(kgdb_call_nmi_hook, NULL, 0);
> - local_irq_disable();
> }
>
> static int __kgdb_notify(struct die_args *args, unsigned long cmd)
> diff --git a/arch/hexagon/kernel/kgdb.c b/arch/hexagon/kernel/kgdb.c
> index 16c24b22d0b2..30fbc491cf45 100644
> --- a/arch/hexagon/kernel/kgdb.c
> +++ b/arch/hexagon/kernel/kgdb.c
> @@ -119,17 +119,12 @@ void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long pc)
>
> /**
> * kgdb_roundup_cpus - Get other CPUs into a holding pattern
> - * @flags: Current IRQ state
> *
> * On SMP systems, we need to get the attention of the other CPUs
> * and get them be in a known state. This should do what is needed
> * to get the other CPUs to call kgdb_wait(). Note that on some arches,
> * the NMI approach is not used for rounding up all the CPUs. For example,
> - * in case of MIPS, smp_call_function() is used to roundup CPUs. In
> - * this case, we have to make sure that interrupts are enabled before
> - * calling smp_call_function(). The argument to this function is
> - * the flags that will be used when restoring the interrupts. There is
> - * local_irq_save() call before kgdb_roundup_cpus().
> + * in case of MIPS, smp_call_function() is used to roundup CPUs.
> *
> * On non-SMP systems, this is not called.
> */
> @@ -139,11 +134,9 @@ static void hexagon_kgdb_nmi_hook(void *ignored)
> kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
> }
>
> -void kgdb_roundup_cpus(unsigned long flags)
> +void kgdb_roundup_cpus(void)
> {
> - local_irq_enable();
> smp_call_function(hexagon_kgdb_nmi_hook, NULL, 0);
> - local_irq_disable();
> }
> #endif
>
> diff --git a/arch/mips/kernel/kgdb.c b/arch/mips/kernel/kgdb.c
> index eb6c0d582626..6671a279966f 100644
> --- a/arch/mips/kernel/kgdb.c
> +++ b/arch/mips/kernel/kgdb.c
> @@ -219,11 +219,9 @@ static void kgdb_call_nmi_hook(void *ignored)
> set_fs(old_fs);
> }
>
> -void kgdb_roundup_cpus(unsigned long flags)
> +void kgdb_roundup_cpus(void)
> {
> - local_irq_enable();
> smp_call_function(kgdb_call_nmi_hook, NULL, 0);
> - local_irq_disable();
> }
>
> static int compute_signal(int tt)
> diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
> index 59c578f865aa..b0e804844be0 100644
> --- a/arch/powerpc/kernel/kgdb.c
> +++ b/arch/powerpc/kernel/kgdb.c
> @@ -124,7 +124,7 @@ static int kgdb_call_nmi_hook(struct pt_regs *regs)
> }
>
> #ifdef CONFIG_SMP
> -void kgdb_roundup_cpus(unsigned long flags)
> +void kgdb_roundup_cpus(void)
> {
> smp_send_debugger_break();
> }
> diff --git a/arch/sh/kernel/kgdb.c b/arch/sh/kernel/kgdb.c
> index 4f04c6638a4d..86b3ea927e42 100644
> --- a/arch/sh/kernel/kgdb.c
> +++ b/arch/sh/kernel/kgdb.c
> @@ -319,11 +319,9 @@ static void kgdb_call_nmi_hook(void *ignored)
> kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
> }
>
> -void kgdb_roundup_cpus(unsigned long flags)
> +void kgdb_roundup_cpus(void)
> {
> - local_irq_enable();
> smp_call_function(kgdb_call_nmi_hook, NULL, 0);
> - local_irq_disable();
> }
>
> static int __kgdb_notify(struct die_args *args, unsigned long cmd)
> diff --git a/arch/sparc/kernel/smp_64.c b/arch/sparc/kernel/smp_64.c
> index 4792e08ad36b..f45d876983f1 100644
> --- a/arch/sparc/kernel/smp_64.c
> +++ b/arch/sparc/kernel/smp_64.c
> @@ -1014,7 +1014,7 @@ void flush_dcache_page_all(struct mm_struct *mm, struct page *page)
> }
>
> #ifdef CONFIG_KGDB
> -void kgdb_roundup_cpus(unsigned long flags)
> +void kgdb_roundup_cpus(void)
> {
> smp_cross_call(&xcall_kgdb_capture, 0, 0, 0);
> }
> diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
> index 8e36f249646e..ac6291a4178d 100644
> --- a/arch/x86/kernel/kgdb.c
> +++ b/arch/x86/kernel/kgdb.c
> @@ -422,21 +422,16 @@ static void kgdb_disable_hw_debug(struct pt_regs *regs)
> #ifdef CONFIG_SMP
> /**
> * kgdb_roundup_cpus - Get other CPUs into a holding pattern
> - * @flags: Current IRQ state
> *
> * On SMP systems, we need to get the attention of the other CPUs
> * and get them be in a known state. This should do what is needed
> * to get the other CPUs to call kgdb_wait(). Note that on some arches,
> * the NMI approach is not used for rounding up all the CPUs. For example,
> - * in case of MIPS, smp_call_function() is used to roundup CPUs. In
> - * this case, we have to make sure that interrupts are enabled before
> - * calling smp_call_function(). The argument to this function is
> - * the flags that will be used when restoring the interrupts. There is
> - * local_irq_save() call before kgdb_roundup_cpus().
> + * in case of MIPS, smp_call_function() is used to roundup CPUs.
> *
> * On non-SMP systems, this is not called.
> */
> -void kgdb_roundup_cpus(unsigned long flags)
> +void kgdb_roundup_cpus(void)
> {
> apic->send_IPI_allbutself(APIC_DM_NMI);
> }
> diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
> index e465bb15912d..05e5b2eb0d32 100644
> --- a/include/linux/kgdb.h
> +++ b/include/linux/kgdb.h
> @@ -178,21 +178,16 @@ kgdb_arch_handle_exception(int vector, int signo, int err_code,
>
> /**
> * kgdb_roundup_cpus - Get other CPUs into a holding pattern
> - * @flags: Current IRQ state
> *
> * On SMP systems, we need to get the attention of the other CPUs
> * and get them into a known state. This should do what is needed
> * to get the other CPUs to call kgdb_wait(). Note that on some arches,
> * the NMI approach is not used for rounding up all the CPUs. For example,
> - * in case of MIPS, smp_call_function() is used to roundup CPUs. In
> - * this case, we have to make sure that interrupts are enabled before
> - * calling smp_call_function(). The argument to this function is
> - * the flags that will be used when restoring the interrupts. There is
> - * local_irq_save() call before kgdb_roundup_cpus().
> + * in case of MIPS, smp_call_function() is used to roundup CPUs.
> *
> * On non-SMP systems, this is not called.
> */
> -extern void kgdb_roundup_cpus(unsigned long flags);
> +extern void kgdb_roundup_cpus(void);
>
> /**
> * kgdb_arch_set_pc - Generic call back to the program counter
> diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
> index 65c0f1363788..f3cadda45f07 100644
> --- a/kernel/debug/debug_core.c
> +++ b/kernel/debug/debug_core.c
> @@ -593,7 +593,7 @@ static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
>
> /* Signal the other CPUs to enter kgdb_wait() */
> else if ((!kgdb_single_step) && kgdb_do_roundup)
> - kgdb_roundup_cpus(flags);
> + kgdb_roundup_cpus();
> #endif
>
> /*
> --
> 2.19.1.568.g152ad8e336-goog
>