| Message ID | 20230601143109.v9.5.I65981105e1f62550b0316625dd1e599deaf9e1aa@changeid (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: Add debug IPI for backtraces / kgdb; try to use NMI for it | expand |
On Thu, Jun 01, 2023 at 02:31:49PM -0700, Douglas Anderson wrote: > From: Sumit Garg <sumit.garg@linaro.org> > > Enable arch_trigger_cpumask_backtrace() support on arm64 using the new > debug IPI. With this arm64 can now get backtraces in cases where > callers of the trigger_xyz_backtrace() class of functions don't check > the return code and implement a fallback. One example is > `kernel.softlockup_all_cpu_backtrace`. This also allows us to > backtrace hard locked up CPUs in cases where the debug IPI is backed > by an NMI (or pseudo NMI). > > Signed-off-by: Sumit Garg <sumit.garg@linaro.org> > Signed-off-by: Douglas Anderson <dianders@chromium.org> > --- > > Changes in v9: > - Added comments that we might not be using NMI always. > - Renamed "NMI IPI" to "debug IPI" since it might not be backed by NMI. > - arch_trigger_cpumask_backtrace() no longer returns bool > > Changes in v8: > - Removed "#ifdef CONFIG_SMP" since arm64 is always SMP > > arch/arm64/include/asm/irq.h | 3 +++ > arch/arm64/kernel/ipi_debug.c | 25 +++++++++++++++++++++++-- > 2 files changed, 26 insertions(+), 2 deletions(-) As with prior patches, I'd prefer if this lived in smp.c with the other IPI logic. > > diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h > index fac08e18bcd5..be2d103f316e 100644 > --- a/arch/arm64/include/asm/irq.h > +++ b/arch/arm64/include/asm/irq.h > @@ -6,6 +6,9 @@ > > #include <asm-generic/irq.h> > > +void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self); > +#define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace > + > struct pt_regs; > > int set_handle_irq(void (*handle_irq)(struct pt_regs *)); > diff --git a/arch/arm64/kernel/ipi_debug.c b/arch/arm64/kernel/ipi_debug.c > index b57833e31eaf..6984ed507e1f 100644 > --- a/arch/arm64/kernel/ipi_debug.c > +++ b/arch/arm64/kernel/ipi_debug.c > @@ -8,6 +8,7 @@ > > #include <linux/interrupt.h> > #include <linux/irq.h> > +#include <linux/nmi.h> > #include <linux/smp.h> > > #include "ipi_debug.h" > @@ -24,11 +25,31 @@ void arm64_debug_ipi(cpumask_t *mask) > __ipi_send_mask(ipi_debug_desc, mask); > } > > +void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self) > +{ > + /* > + * NOTE: though nmi_trigger_cpumask_backtrace has "nmi_" in the name, > + * nothing about it truly needs to be backed by an NMI, it's just that > + * it's _allowed_ to be called from an NMI. If set_smp_debug_ipi() > + * failed to get an NMI (or pseudo-NMI) this will just be backed by a > + * regular IPI. > + */ > + nmi_trigger_cpumask_backtrace(mask, exclude_self, arm64_debug_ipi); > +} > + > static irqreturn_t ipi_debug_handler(int irq, void *data) > { > - /* nop, NMI handlers for special features can be added here. */ > + irqreturn_t ret = IRQ_NONE; > + > + /* > + * NOTE: Just like in arch_trigger_cpumask_backtrace(), we're calling > + * a function with "nmi_" in the name but it works fine even if we > + * are using a regulaor IPI. > + */ > + if (nmi_cpu_backtrace(get_irq_regs())) > + ret = IRQ_HANDLED; > Does this need the printk_deferred_{enter,exit}() that 32-bit arm has? Thanks, Mark. > - return IRQ_NONE; > + return ret; > } > > void debug_ipi_setup(void) > -- > 2.41.0.rc2.161.g9c6817b8e7-goog >
Hi, On Mon, Aug 7, 2023 at 3:23 AM Mark Rutland <mark.rutland@arm.com> wrote: > > On Thu, Jun 01, 2023 at 02:31:49PM -0700, Douglas Anderson wrote: > > From: Sumit Garg <sumit.garg@linaro.org> > > > > Enable arch_trigger_cpumask_backtrace() support on arm64 using the new > > debug IPI. With this arm64 can now get backtraces in cases where > > callers of the trigger_xyz_backtrace() class of functions don't check > > the return code and implement a fallback. One example is > > `kernel.softlockup_all_cpu_backtrace`. This also allows us to > > backtrace hard locked up CPUs in cases where the debug IPI is backed > > by an NMI (or pseudo NMI). > > > > Signed-off-by: Sumit Garg <sumit.garg@linaro.org> > > Signed-off-by: Douglas Anderson <dianders@chromium.org> > > --- > > > > Changes in v9: > > - Added comments that we might not be using NMI always. > > - Renamed "NMI IPI" to "debug IPI" since it might not be backed by NMI. > > - arch_trigger_cpumask_backtrace() no longer returns bool > > > > Changes in v8: > > - Removed "#ifdef CONFIG_SMP" since arm64 is always SMP > > > > arch/arm64/include/asm/irq.h | 3 +++ > > arch/arm64/kernel/ipi_debug.c | 25 +++++++++++++++++++++++-- > > 2 files changed, 26 insertions(+), 2 deletions(-) > > As with prior patches, I'd prefer if this lived in smp.c with the other IPI > logic. > > > > > diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h > > index fac08e18bcd5..be2d103f316e 100644 > > --- a/arch/arm64/include/asm/irq.h > > +++ b/arch/arm64/include/asm/irq.h > > @@ -6,6 +6,9 @@ > > > > #include <asm-generic/irq.h> > > > > +void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self); > > +#define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace > > + > > struct pt_regs; > > > > int set_handle_irq(void (*handle_irq)(struct pt_regs *)); > > diff --git a/arch/arm64/kernel/ipi_debug.c b/arch/arm64/kernel/ipi_debug.c > > index b57833e31eaf..6984ed507e1f 100644 > > --- a/arch/arm64/kernel/ipi_debug.c > > +++ b/arch/arm64/kernel/ipi_debug.c > > @@ -8,6 +8,7 @@ > > > > #include <linux/interrupt.h> > > #include <linux/irq.h> > > +#include <linux/nmi.h> > > #include <linux/smp.h> > > > > #include "ipi_debug.h" > > @@ -24,11 +25,31 @@ void arm64_debug_ipi(cpumask_t *mask) > > __ipi_send_mask(ipi_debug_desc, mask); > > } > > > > +void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self) > > +{ > > + /* > > + * NOTE: though nmi_trigger_cpumask_backtrace has "nmi_" in the name, > > + * nothing about it truly needs to be backed by an NMI, it's just that > > + * it's _allowed_ to be called from an NMI. If set_smp_debug_ipi() > > + * failed to get an NMI (or pseudo-NMI) this will just be backed by a > > + * regular IPI. > > + */ > > + nmi_trigger_cpumask_backtrace(mask, exclude_self, arm64_debug_ipi); > > +} > > + > > static irqreturn_t ipi_debug_handler(int irq, void *data) > > { > > - /* nop, NMI handlers for special features can be added here. */ > > + irqreturn_t ret = IRQ_NONE; > > + > > + /* > > + * NOTE: Just like in arch_trigger_cpumask_backtrace(), we're calling > > + * a function with "nmi_" in the name but it works fine even if we > > + * are using a regulaor IPI. > > + */ > > + if (nmi_cpu_backtrace(get_irq_regs())) > > + ret = IRQ_HANDLED; > > > > Does this need the printk_deferred_{enter,exit}() that 32-bit arm has? I don't _think_ so, but I also don't _think_ it's needed for arm32. ;-) Let me explain my logic and you can tell me if it sounds right to you. If we're doing the backtrace in pseudo-NMI context then we definitely don't need it. Specifically, the printk_deferred_{enter,exit}() just manages the per-cpu "printk_context" value. That value doesn't matter if "in_nmi()" returns true. If we're _not_ doing the backtrace in pseudo-NMI context then I think we also don't need it. After all, if we're not in pseudo-NMI context then it's perfectly fine to print, right? While it's hard to know 100% for sure, my best guess is that in arm this might have helped prevent stack traces from getting interspersed among one another. I guess this is no longer needed as of commit 55d6af1d6688 ("lib/nmi_backtrace: explicitly serialize banner and regs")? In any case, when I tested this earlier things seemed to printout fine without it... That being said, it wouldn't hurt to include it here and I'll do it if you want. -Doug
On Mon, Aug 21, 2023 at 05:06:50PM -0700, Doug Anderson wrote: > On Mon, Aug 7, 2023 at 3:23 AM Mark Rutland <mark.rutland@arm.com> wrote: > > On Thu, Jun 01, 2023 at 02:31:49PM -0700, Douglas Anderson wrote: > > > From: Sumit Garg <sumit.garg@linaro.org> > > > static irqreturn_t ipi_debug_handler(int irq, void *data) > > > { > > > - /* nop, NMI handlers for special features can be added here. */ > > > + irqreturn_t ret = IRQ_NONE; > > > + > > > + /* > > > + * NOTE: Just like in arch_trigger_cpumask_backtrace(), we're calling > > > + * a function with "nmi_" in the name but it works fine even if we > > > + * are using a regulaor IPI. > > > + */ > > > + if (nmi_cpu_backtrace(get_irq_regs())) > > > + ret = IRQ_HANDLED; > > > > > > > Does this need the printk_deferred_{enter,exit}() that 32-bit arm has? > > I don't _think_ so, but I also don't _think_ it's needed for arm32. > ;-) Let me explain my logic and you can tell me if it sounds right to > you. > > If we're doing the backtrace in pseudo-NMI context then we definitely > don't need it. Specifically, the printk_deferred_{enter,exit}() just > manages the per-cpu "printk_context" value. That value doesn't matter > if "in_nmi()" returns true. > > If we're _not_ doing the backtrace in pseudo-NMI context then I think > we also don't need it. After all, if we're not in pseudo-NMI context > then it's perfectly fine to print, right? > > While it's hard to know 100% for sure, my best guess is that in arm > this might have helped prevent stack traces from getting interspersed > among one another. I guess this is no longer needed as of commit > 55d6af1d6688 ("lib/nmi_backtrace: explicitly serialize banner and > regs")? In any case, when I tested this earlier things seemed to > printout fine without it... Thanks for that explanation; that makes sense to me! Looking around a bit I see that x86 doesn't bother either. > That being said, it wouldn't hurt to include it here and I'll do it if you > want. No need -- I'm happy without it. Thanks, Mark.
diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h index fac08e18bcd5..be2d103f316e 100644 --- a/arch/arm64/include/asm/irq.h +++ b/arch/arm64/include/asm/irq.h @@ -6,6 +6,9 @@ #include <asm-generic/irq.h> +void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self); +#define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace + struct pt_regs; int set_handle_irq(void (*handle_irq)(struct pt_regs *)); diff --git a/arch/arm64/kernel/ipi_debug.c b/arch/arm64/kernel/ipi_debug.c index b57833e31eaf..6984ed507e1f 100644 --- a/arch/arm64/kernel/ipi_debug.c +++ b/arch/arm64/kernel/ipi_debug.c @@ -8,6 +8,7 @@ #include <linux/interrupt.h> #include <linux/irq.h> +#include <linux/nmi.h> #include <linux/smp.h> #include "ipi_debug.h" @@ -24,11 +25,31 @@ void arm64_debug_ipi(cpumask_t *mask) __ipi_send_mask(ipi_debug_desc, mask); } +void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self) +{ + /* + * NOTE: though nmi_trigger_cpumask_backtrace has "nmi_" in the name, + * nothing about it truly needs to be backed by an NMI, it's just that + * it's _allowed_ to be called from an NMI. If set_smp_debug_ipi() + * failed to get an NMI (or pseudo-NMI) this will just be backed by a + * regular IPI. + */ + nmi_trigger_cpumask_backtrace(mask, exclude_self, arm64_debug_ipi); +} + static irqreturn_t ipi_debug_handler(int irq, void *data) { - /* nop, NMI handlers for special features can be added here. */ + irqreturn_t ret = IRQ_NONE; + + /* + * NOTE: Just like in arch_trigger_cpumask_backtrace(), we're calling + * a function with "nmi_" in the name but it works fine even if we + * are using a regulaor IPI. + */ + if (nmi_cpu_backtrace(get_irq_regs())) + ret = IRQ_HANDLED; - return IRQ_NONE; + return ret; } void debug_ipi_setup(void)