[PATCHv13 0/5] *** Detect interrupt storm in softlockup ***

[PATCHv13 0/5] *** Detect interrupt storm in softlockup ***

[Bitao Hu]

Hi, guys.
I have implemented a low-overhead method for detecting interrupt
storm in softlockup. Please review it, all comments are welcome.

Changes from v12 to v13:

- Update patch #1 based on the latest kernel code.

- From Thomas, split patch #1 into two. The new patch #1 converts
kstat_irqs into a struct with just the count in it; the new
patch #2 introduces a snapshot mechanism for interrupt statistics.
Due to the code being split, I removed the Reviewed-by tags from
LiuSong and Douglas in patch #1 and patch #2.
Please review it again, and all comments are welcome.

- Revised the comment for using printk() instead of pr_crit() to make
the reasoning clearer.

Changes from v11 to v12:

- From Douglas and Thomas, add a new kconfig knob save memory when
the softlock detector code is not enabled.

- Adjust the order of the patches; patch #1 and patch #2 are related
to genirq, while patch #3 and patch #4 are related to watchdog/softlockup,
making the dependency relationships clearer.

- Add the 'Reviewed-by' tag of Douglas.

Changes from v10 to v11:

- Only patch #2 and patch #3 have been changed.

- Add comments to explain each field of 'struct irqstat' in patch #2.

- Split the inner summation logic out of kstat_irqs() and encapsulate
it into kstat_irqs_desc() in patch #3.

- Adopt Thomas's change log for patch #3.

- Add the 'Reviewed-by' tag of Liu Song.

Changes from v9 to v10:

- The two patches related to 'watchdog/softlockup' remain unchanged.

- The majority of the work related to 'genirq' is contributed by
Thomas, indicated by adding 'Originally-by' tag. And I'd like to
express my gratitude for Thomas's contributions and guidance here.

- Adopt Thomas's change log for the snapshot mechanism for interrupt
statistics.

- Split unrelated change in patch #2 into a separate patch #3.

Changes from v8 to v9:

- Patch #1 remains unchanged.

- From Thomas Gleixner, split patch #2 into two patches. Interrupt
infrastructure first and then the actual usage site in the
watchdog code.

Changes from v7 to v8:

- From Thomas Gleixner, implement statistics within the interrupt
core code and provide sensible interfaces for the watchdog code.

- Patch #1 remains unchanged. Patch #2 has significant changes
based on Thomas's suggestions, which is why I have removed
Liu Song and Douglas's Reviewed-by from patch #2. Please review
it again, and all comments are welcome.

Changes from v6 to v7:

- Remove "READ_ONCE" in "start_counting_irqs"

- Replace the hard-coded 5 with "NUM_SAMPLE_PERIODS" macro in
"set_sample_period".

- Add empty lines to help with reading the code.

- Remove the branch that processes IRQs where "counts_diff = 0".

- Add the Reviewed-by of Liu Song and Douglas.

Changes from v5 to v6:

- Use "./scripts/checkpatch.pl --strict" to get a few extra
style nits and fix them.

- Squash patch #3 into patch #1, and wrapp the help text to
80 columns.

- Sort existing headers alphabetically in watchdog.c

- Drop "softlockup_hardirq_cpus", just read "hardirq_counts"
and see if it's non-NULL.

- Store "nr_irqs" in a local variable.

- Simplify the calculation of "cpu_diff".

Changes from v4 to v5:

- Rearranging variable placement to make code look neater.

Changes from v3 to v4:

- Renaming some variable and function names to make the code logic
more readable.

- Change the code location to avoid predeclaring.

- Just swap rather than a double loop in tabulate_irq_count.

- Since nr_irqs has the potential to grow at runtime, bounds-check
logic has been implemented.

- Add SOFTLOCKUP_DETECTOR_INTR_STORM Kconfig knob.

Changes from v2 to v3:

- From Liu Song, using enum instead of macro for cpu_stats, shortening
the name 'idx_to_stat' to 'stats', adding 'get_16bit_precesion' instead
of using right shift operations, and using 'struct irq_counts'.

- From kernel robot test, using '__this_cpu_read' and '__this_cpu_write'
instead of accessing to an per-cpu array directly, in order to avoid
this warning.
'sparse: incorrect type in initializer (different modifiers)'

Changes from v1 to v2:

- From Douglas, optimize the memory of cpustats. With the maximum number
of CPUs, that's now this.
2 * 8192 * 4 + 1 * 8192 * 5 * 4 + 1 * 8192 = 237,568 bytes.

- From Liu Song, refactor the code format and add necessary comments.

- From Douglas, use interrupt counts instead of interrupt time to
determine the cause of softlockup.

- Remove the cmdline parameter added in PATCHv1.

Bitao Hu (5):
  genirq: Convert kstat_irqs to a struct
  genirq: Provide a snapshot mechanism for interrupt statistics
  genirq: Avoid summation loops for /proc/interrupts
  watchdog/softlockup: low-overhead detection of interrupt storm
  watchdog/softlockup: report the most frequent interrupts

 arch/mips/dec/setup.c                |   2 +-
 arch/parisc/kernel/smp.c             |   2 +-
 arch/powerpc/kvm/book3s_hv_rm_xics.c |   2 +-
 include/linux/irqdesc.h              |  16 +-
 include/linux/kernel_stat.h          |   8 +
 kernel/irq/Kconfig                   |   4 +
 kernel/irq/internals.h               |   4 +-
 kernel/irq/irqdesc.c                 |  50 +++++--
 kernel/irq/proc.c                    |   9 +-
 kernel/watchdog.c                    | 215 ++++++++++++++++++++++++++-
 lib/Kconfig.debug                    |  14 ++
 scripts/gdb/linux/interrupts.py      |   6 +-
 12 files changed, 302 insertions(+), 30 deletions(-)

-- 
2.37.1 (Apple Git-137.1)

[PATCHv13 1/5] genirq: Convert kstat_irqs to a struct

[Bitao Hu]

The irq_desc::kstat_irqs member is a per-CPU variable of type int, and
it is only capable of counting. The snapshot mechanism for interrupt
statistics will be added soon, which requires an additional variable to
store snapshot. To facilitate expansion, convert kstat_irqs here to
a struct containing only the count.

Originally-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Bitao Hu <yaoma@linux.alibaba.com>
---
 arch/mips/dec/setup.c                |  2 +-
 arch/parisc/kernel/smp.c             |  2 +-
 arch/powerpc/kvm/book3s_hv_rm_xics.c |  2 +-
 include/linux/irqdesc.h              | 12 ++++++++++--
 kernel/irq/internals.h               |  2 +-
 kernel/irq/irqdesc.c                 |  9 ++++-----
 kernel/irq/proc.c                    |  5 ++---
 scripts/gdb/linux/interrupts.py      |  6 +++---
 8 files changed, 23 insertions(+), 17 deletions(-)

diff --git a/arch/mips/dec/setup.c b/arch/mips/dec/setup.c
index 6c3704f51d0d..87f0a1436bf9 100644
--- a/arch/mips/dec/setup.c
+++ b/arch/mips/dec/setup.c
@@ -756,7 +756,7 @@ void __init arch_init_irq(void)
 				NULL))
 			pr_err("Failed to register fpu interrupt\n");
 		desc_fpu = irq_to_desc(irq_fpu);
-		fpu_kstat_irq = this_cpu_ptr(desc_fpu->kstat_irqs);
+		fpu_kstat_irq = this_cpu_ptr(&desc_fpu->kstat_irqs->cnt);
 	}
 	if (dec_interrupt[DEC_IRQ_CASCADE] >= 0) {
 		if (request_irq(dec_interrupt[DEC_IRQ_CASCADE], no_action,
diff --git a/arch/parisc/kernel/smp.c b/arch/parisc/kernel/smp.c
index 444154271f23..800eb64e91ad 100644
--- a/arch/parisc/kernel/smp.c
+++ b/arch/parisc/kernel/smp.c
@@ -344,7 +344,7 @@ static int smp_boot_one_cpu(int cpuid, struct task_struct *idle)
 		struct irq_desc *desc = irq_to_desc(i);
 
 		if (desc && desc->kstat_irqs)
-			*per_cpu_ptr(desc->kstat_irqs, cpuid) = 0;
+			*per_cpu_ptr(desc->kstat_irqs, cpuid) = (struct irqstat) { };
 	}
 #endif
 
diff --git a/arch/powerpc/kvm/book3s_hv_rm_xics.c b/arch/powerpc/kvm/book3s_hv_rm_xics.c
index e42984878503..f2636414d82a 100644
--- a/arch/powerpc/kvm/book3s_hv_rm_xics.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_xics.c
@@ -837,7 +837,7 @@ static inline void this_cpu_inc_rm(unsigned int __percpu *addr)
  */
 static void kvmppc_rm_handle_irq_desc(struct irq_desc *desc)
 {
-	this_cpu_inc_rm(desc->kstat_irqs);
+	this_cpu_inc_rm(&desc->kstat_irqs->cnt);
 	__this_cpu_inc(kstat.irqs_sum);
 }
 
diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
index d9451d456a73..c28612674acb 100644
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -17,6 +17,14 @@ struct irq_desc;
 struct irq_domain;
 struct pt_regs;
 
+/**
+ * struct irqstat - interrupt statistics
+ * @cnt:	real-time interrupt count
+ */
+struct irqstat {
+	unsigned int	cnt;
+};
+
 /**
  * struct irq_desc - interrupt descriptor
  * @irq_common_data:	per irq and chip data passed down to chip functions
@@ -55,7 +63,7 @@ struct pt_regs;
 struct irq_desc {
 	struct irq_common_data	irq_common_data;
 	struct irq_data		irq_data;
-	unsigned int __percpu	*kstat_irqs;
+	struct irqstat __percpu	*kstat_irqs;
 	irq_flow_handler_t	handle_irq;
 	struct irqaction	*action;	/* IRQ action list */
 	unsigned int		status_use_accessors;
@@ -119,7 +127,7 @@ extern struct irq_desc irq_desc[NR_IRQS];
 static inline unsigned int irq_desc_kstat_cpu(struct irq_desc *desc,
 					      unsigned int cpu)
 {
-	return desc->kstat_irqs ? *per_cpu_ptr(desc->kstat_irqs, cpu) : 0;
+	return desc->kstat_irqs ? per_cpu(desc->kstat_irqs->cnt, cpu) : 0;
 }
 
 static inline struct irq_desc *irq_data_to_desc(struct irq_data *data)
diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index bcc7f21db9ee..1d92532c2aae 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -258,7 +258,7 @@ static inline void irq_state_set_masked(struct irq_desc *desc)
 
 static inline void __kstat_incr_irqs_this_cpu(struct irq_desc *desc)
 {
-	__this_cpu_inc(*desc->kstat_irqs);
+	__this_cpu_inc(desc->kstat_irqs->cnt);
 	__this_cpu_inc(kstat.irqs_sum);
 }
 
diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index 4c6b32318ce3..b59b79200ad7 100644
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -134,7 +134,7 @@ static void desc_set_defaults(unsigned int irq, struct irq_desc *desc, int node,
 	desc->name = NULL;
 	desc->owner = owner;
 	for_each_possible_cpu(cpu)
-		*per_cpu_ptr(desc->kstat_irqs, cpu) = 0;
+		*per_cpu_ptr(desc->kstat_irqs, cpu) = (struct irqstat) { };
 	desc_smp_init(desc, node, affinity);
 }
 
@@ -186,7 +186,7 @@ static int init_desc(struct irq_desc *desc, int irq, int node,
 		     const struct cpumask *affinity,
 		     struct module *owner)
 {
-	desc->kstat_irqs = alloc_percpu(unsigned int);
+	desc->kstat_irqs = alloc_percpu(struct irqstat);
 	if (!desc->kstat_irqs)
 		return -ENOMEM;
 
@@ -968,8 +968,7 @@ unsigned int kstat_irqs_cpu(unsigned int irq, int cpu)
 {
 	struct irq_desc *desc = irq_to_desc(irq);
 
-	return desc && desc->kstat_irqs ?
-			*per_cpu_ptr(desc->kstat_irqs, cpu) : 0;
+	return desc && desc->kstat_irqs ? per_cpu(desc->kstat_irqs->cnt, cpu) : 0;
 }
 
 static bool irq_is_nmi(struct irq_desc *desc)
@@ -991,7 +990,7 @@ static unsigned int kstat_irqs(unsigned int irq)
 		return data_race(desc->tot_count);
 
 	for_each_possible_cpu(cpu)
-		sum += data_race(*per_cpu_ptr(desc->kstat_irqs, cpu));
+		sum += data_race(per_cpu(desc->kstat_irqs->cnt, cpu));
 	return sum;
 }
 
diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index 623b8136e9af..6954e0a02047 100644
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -490,7 +490,7 @@ int show_interrupts(struct seq_file *p, void *v)
 
 	if (desc->kstat_irqs) {
 		for_each_online_cpu(j)
-			any_count |= data_race(*per_cpu_ptr(desc->kstat_irqs, j));
+			any_count |= data_race(per_cpu(desc->kstat_irqs->cnt, j));
 	}
 
 	if ((!desc->action || irq_desc_is_chained(desc)) && !any_count)
@@ -498,8 +498,7 @@ int show_interrupts(struct seq_file *p, void *v)
 
 	seq_printf(p, "%*d: ", prec, i);
 	for_each_online_cpu(j)
-		seq_printf(p, "%10u ", desc->kstat_irqs ?
-					*per_cpu_ptr(desc->kstat_irqs, j) : 0);
+		seq_printf(p, "%10u ", desc->kstat_irqs ? per_cpu(desc->kstat_irqs->cnt, j) : 0);
 
 	raw_spin_lock_irqsave(&desc->lock, flags);
 	if (desc->irq_data.chip) {
diff --git a/scripts/gdb/linux/interrupts.py b/scripts/gdb/linux/interrupts.py
index 66ae5c7690cf..616a5f26377a 100644
--- a/scripts/gdb/linux/interrupts.py
+++ b/scripts/gdb/linux/interrupts.py
@@ -37,7 +37,7 @@ def show_irq_desc(prec, irq):
     any_count = 0
     if desc['kstat_irqs']:
         for cpu in cpus.each_online_cpu():
-            any_count += cpus.per_cpu(desc['kstat_irqs'], cpu)
+            any_count += cpus.per_cpu(desc['kstat_irqs'], cpu)['cnt']
 
     if (desc['action'] == 0 or irq_desc_is_chained(desc)) and any_count == 0:
         return text;
@@ -45,7 +45,7 @@ def show_irq_desc(prec, irq):
     text += "%*d: " % (prec, irq)
     for cpu in cpus.each_online_cpu():
         if desc['kstat_irqs']:
-            count = cpus.per_cpu(desc['kstat_irqs'], cpu)
+            count = cpus.per_cpu(desc['kstat_irqs'], cpu)['cnt']
         else:
             count = 0
         text += "%10u" % (count)
@@ -177,7 +177,7 @@ def arm_common_show_interrupts(prec):
         if desc == 0:
             continue
         for cpu in cpus.each_online_cpu():
-            text += "%10u" % (cpus.per_cpu(desc['kstat_irqs'], cpu))
+            text += "%10u" % (cpus.per_cpu(desc['kstat_irqs'], cpu)['cnt'])
         text += "      %s" % (ipi_types[ipi].string())
         text += "\n"
     return text
-- 
2.37.1 (Apple Git-137.1)

[PATCHv13 2/5] genirq: Provide a snapshot mechanism for interrupt statistics

[Bitao Hu]

The soft lockup detector lacks a mechanism to identify interrupt storms
as root cause of a lockup. To enable this the detector needs a
mechanism to snapshot the interrupt count statistics on a CPU when the
detector observes a potential lockup scenario and compare that against
the interrupt count when it warns about the lockup later on. The number
of interrupts in that period give a hint whether the lockup might be
caused by an interrupt storm.

Instead of having extra storage in the lockup detector and accessing
the internals of the interrupt descriptor directly, add a snapshot
member to the per CPU irq_desc::kstat_irq structure and provide
interfaces to take a snapshot of all interrupts on the current CPU
and to retrieve the delta of a specific interrupt later on.

Originally-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Bitao Hu <yaoma@linux.alibaba.com>
---
 include/linux/irqdesc.h     |  4 ++++
 include/linux/kernel_stat.h |  8 ++++++++
 kernel/irq/Kconfig          |  4 ++++
 kernel/irq/irqdesc.c        | 25 +++++++++++++++++++++++++
 4 files changed, 41 insertions(+)

diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
index c28612674acb..fd091c35d572 100644
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -20,9 +20,13 @@ struct pt_regs;
 /**
  * struct irqstat - interrupt statistics
  * @cnt:	real-time interrupt count
+ * @ref:	snapshot of interrupt count
  */
 struct irqstat {
 	unsigned int	cnt;
+#ifdef CONFIG_GENERIC_IRQ_STAT_SNAPSHOT
+	unsigned int	ref;
+#endif
 };
 
 /**
diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h
index 9935f7ecbfb9..9c042c6384bb 100644
--- a/include/linux/kernel_stat.h
+++ b/include/linux/kernel_stat.h
@@ -79,6 +79,14 @@ static inline unsigned int kstat_cpu_softirqs_sum(int cpu)
 	return sum;
 }
 
+#ifdef CONFIG_GENERIC_IRQ_STAT_SNAPSHOT
+extern void kstat_snapshot_irqs(void);
+extern unsigned int kstat_get_irq_since_snapshot(unsigned int irq);
+#else
+static inline void kstat_snapshot_irqs(void) { }
+static inline unsigned int kstat_get_irq_since_snapshot(unsigned int irq) { return 0; }
+#endif
+
 /*
  * Number of interrupts per specific IRQ source, since bootup
  */
diff --git a/kernel/irq/Kconfig b/kernel/irq/Kconfig
index 2531f3496ab6..529adb1f5859 100644
--- a/kernel/irq/Kconfig
+++ b/kernel/irq/Kconfig
@@ -108,6 +108,10 @@ config GENERIC_IRQ_MATRIX_ALLOCATOR
 config GENERIC_IRQ_RESERVATION_MODE
 	bool
 
+# Snapshot for interrupt statistics
+config GENERIC_IRQ_STAT_SNAPSHOT
+	bool
+
 # Support forced irq threading
 config IRQ_FORCED_THREADING
        bool
diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index b59b79200ad7..f348faffa7b4 100644
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -994,6 +994,31 @@ static unsigned int kstat_irqs(unsigned int irq)
 	return sum;
 }
 
+#ifdef CONFIG_GENERIC_IRQ_STAT_SNAPSHOT
+
+void kstat_snapshot_irqs(void)
+{
+	struct irq_desc *desc;
+	unsigned int irq;
+
+	for_each_irq_desc(irq, desc) {
+		if (!desc->kstat_irqs)
+			continue;
+		this_cpu_write(desc->kstat_irqs->ref, this_cpu_read(desc->kstat_irqs->cnt));
+	}
+}
+
+unsigned int kstat_get_irq_since_snapshot(unsigned int irq)
+{
+	struct irq_desc *desc = irq_to_desc(irq);
+
+	if (!desc || !desc->kstat_irqs)
+		return 0;
+	return this_cpu_read(desc->kstat_irqs->cnt) - this_cpu_read(desc->kstat_irqs->ref);
+}
+
+#endif
+
 /**
  * kstat_irqs_usr - Get the statistics for an interrupt from thread context
  * @irq:	The interrupt number
-- 
2.37.1 (Apple Git-137.1)

[PATCHv13 3/5] genirq: Avoid summation loops for /proc/interrupts

[Bitao Hu]

show_interrupts() unconditionally accumulates the per CPU interrupt
statistics to determine whether an interrupt was ever raised.

This can be avoided for all interrupts which are not strictly per CPU
and not of type NMI because those interrupts provide already an
accumulated counter. The required logic is already implemented in
kstat_irqs().

Split the inner access logic out of kstat_irqs() and use it for
kstat_irqs() and show_interrupts() to avoid the accumulation loop
when possible.

Originally-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Bitao Hu <yaoma@linux.alibaba.com>
Reviewed-by: Liu Song <liusong@linux.alibaba.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
---
 kernel/irq/internals.h |  2 ++
 kernel/irq/irqdesc.c   | 16 +++++++++++-----
 kernel/irq/proc.c      |  6 ++----
 3 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index 1d92532c2aae..6c43ef3e7308 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -98,6 +98,8 @@ extern void mask_irq(struct irq_desc *desc);
 extern void unmask_irq(struct irq_desc *desc);
 extern void unmask_threaded_irq(struct irq_desc *desc);
 
+extern unsigned int kstat_irqs_desc(struct irq_desc *desc, const struct cpumask *cpumask);
+
 #ifdef CONFIG_SPARSE_IRQ
 static inline void irq_mark_irq(unsigned int irq) { }
 #else
diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index f348faffa7b4..382093196210 100644
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -976,24 +976,30 @@ static bool irq_is_nmi(struct irq_desc *desc)
 	return desc->istate & IRQS_NMI;
 }
 
-static unsigned int kstat_irqs(unsigned int irq)
+unsigned int kstat_irqs_desc(struct irq_desc *desc, const struct cpumask *cpumask)
 {
-	struct irq_desc *desc = irq_to_desc(irq);
 	unsigned int sum = 0;
 	int cpu;
 
-	if (!desc || !desc->kstat_irqs)
-		return 0;
 	if (!irq_settings_is_per_cpu_devid(desc) &&
 	    !irq_settings_is_per_cpu(desc) &&
 	    !irq_is_nmi(desc))
 		return data_race(desc->tot_count);
 
-	for_each_possible_cpu(cpu)
+	for_each_cpu(cpu, cpumask)
 		sum += data_race(per_cpu(desc->kstat_irqs->cnt, cpu));
 	return sum;
 }
 
+static unsigned int kstat_irqs(unsigned int irq)
+{
+	struct irq_desc *desc = irq_to_desc(irq);
+
+	if (!desc || !desc->kstat_irqs)
+		return 0;
+	return kstat_irqs_desc(desc, cpu_possible_mask);
+}
+
 #ifdef CONFIG_GENERIC_IRQ_STAT_SNAPSHOT
 
 void kstat_snapshot_irqs(void)
diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index 6954e0a02047..5c320c3f10a7 100644
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -488,10 +488,8 @@ int show_interrupts(struct seq_file *p, void *v)
 	if (!desc || irq_settings_is_hidden(desc))
 		goto outsparse;
 
-	if (desc->kstat_irqs) {
-		for_each_online_cpu(j)
-			any_count |= data_race(per_cpu(desc->kstat_irqs->cnt, j));
-	}
+	if (desc->kstat_irqs)
+		any_count = kstat_irqs_desc(desc, cpu_online_mask);
 
 	if ((!desc->action || irq_desc_is_chained(desc)) && !any_count)
 		goto outsparse;
-- 
2.37.1 (Apple Git-137.1)

[PATCHv13 4/5] watchdog/softlockup: low-overhead detection of interrupt storm

[Bitao Hu]

The following softlockup is caused by interrupt storm, but it cannot be
identified from the call tree. Because the call tree is just a snapshot
and doesn't fully capture the behavior of the CPU during the soft lockup.
  watchdog: BUG: soft lockup - CPU#28 stuck for 23s! [fio:83921]
  ...
  Call trace:
    __do_softirq+0xa0/0x37c
    __irq_exit_rcu+0x108/0x140
    irq_exit+0x14/0x20
    __handle_domain_irq+0x84/0xe0
    gic_handle_irq+0x80/0x108
    el0_irq_naked+0x50/0x58

Therefore, I think it is necessary to report CPU utilization during the
softlockup_thresh period (report once every sample_period, for a total
of 5 reportings), like this:
  watchdog: BUG: soft lockup - CPU#28 stuck for 23s! [fio:83921]
  CPU#28 Utilization every 4s during lockup:
    #1: 0% system, 0% softirq, 100% hardirq, 0% idle
    #2: 0% system, 0% softirq, 100% hardirq, 0% idle
    #3: 0% system, 0% softirq, 100% hardirq, 0% idle
    #4: 0% system, 0% softirq, 100% hardirq, 0% idle
    #5: 0% system, 0% softirq, 100% hardirq, 0% idle
  ...

This would be helpful in determining whether an interrupt storm has
occurred or in identifying the cause of the softlockup. The criteria for
determination are as follows:
  a. If the hardirq utilization is high, then interrupt storm should be
  considered and the root cause cannot be determined from the call tree.
  b. If the softirq utilization is high, then we could analyze the call
  tree but it may cannot reflect the root cause.
  c. If the system utilization is high, then we could analyze the root
  cause from the call tree.

The mechanism requires a considerable amount of global storage space
when configured for the maximum number of CPUs. Therefore, adding a
SOFTLOCKUP_DETECTOR_INTR_STORM Kconfig knob that defaults to "yes"
if the max number of CPUs is <= 128.

Signed-off-by: Bitao Hu <yaoma@linux.alibaba.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Liu Song <liusong@linux.alibaba.com>
---
 kernel/watchdog.c | 99 ++++++++++++++++++++++++++++++++++++++++++++++-
 lib/Kconfig.debug | 14 +++++++
 2 files changed, 112 insertions(+), 1 deletion(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index d7b2125503af..ef8ebd31fdab 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -16,6 +16,8 @@
 #include <linux/cpu.h>
 #include <linux/nmi.h>
 #include <linux/init.h>
+#include <linux/kernel_stat.h>
+#include <linux/math64.h>
 #include <linux/module.h>
 #include <linux/sysctl.h>
 #include <linux/tick.h>
@@ -35,6 +37,8 @@ static DEFINE_MUTEX(watchdog_mutex);
 # define WATCHDOG_HARDLOCKUP_DEFAULT	0
 #endif
 
+#define NUM_SAMPLE_PERIODS	5
+
 unsigned long __read_mostly watchdog_enabled;
 int __read_mostly watchdog_user_enabled = 1;
 static int __read_mostly watchdog_hardlockup_user_enabled = WATCHDOG_HARDLOCKUP_DEFAULT;
@@ -333,6 +337,96 @@ __setup("watchdog_thresh=", watchdog_thresh_setup);
 
 static void __lockup_detector_cleanup(void);
 
+#ifdef CONFIG_SOFTLOCKUP_DETECTOR_INTR_STORM
+enum stats_per_group {
+	STATS_SYSTEM,
+	STATS_SOFTIRQ,
+	STATS_HARDIRQ,
+	STATS_IDLE,
+	NUM_STATS_PER_GROUP,
+};
+
+static const enum cpu_usage_stat tracked_stats[NUM_STATS_PER_GROUP] = {
+	CPUTIME_SYSTEM,
+	CPUTIME_SOFTIRQ,
+	CPUTIME_IRQ,
+	CPUTIME_IDLE,
+};
+
+static DEFINE_PER_CPU(u16, cpustat_old[NUM_STATS_PER_GROUP]);
+static DEFINE_PER_CPU(u8, cpustat_util[NUM_SAMPLE_PERIODS][NUM_STATS_PER_GROUP]);
+static DEFINE_PER_CPU(u8, cpustat_tail);
+
+/*
+ * We don't need nanosecond resolution. A granularity of 16ms is
+ * sufficient for our precision, allowing us to use u16 to store
+ * cpustats, which will roll over roughly every ~1000 seconds.
+ * 2^24 ~= 16 * 10^6
+ */
+static u16 get_16bit_precision(u64 data_ns)
+{
+	return data_ns >> 24LL; /* 2^24ns ~= 16.8ms */
+}
+
+static void update_cpustat(void)
+{
+	int i;
+	u8 util;
+	u16 old_stat, new_stat;
+	struct kernel_cpustat kcpustat;
+	u64 *cpustat = kcpustat.cpustat;
+	u8 tail = __this_cpu_read(cpustat_tail);
+	u16 sample_period_16 = get_16bit_precision(sample_period);
+
+	kcpustat_cpu_fetch(&kcpustat, smp_processor_id());
+
+	for (i = 0; i < NUM_STATS_PER_GROUP; i++) {
+		old_stat = __this_cpu_read(cpustat_old[i]);
+		new_stat = get_16bit_precision(cpustat[tracked_stats[i]]);
+		util = DIV_ROUND_UP(100 * (new_stat - old_stat), sample_period_16);
+		__this_cpu_write(cpustat_util[tail][i], util);
+		__this_cpu_write(cpustat_old[i], new_stat);
+	}
+
+	__this_cpu_write(cpustat_tail, (tail + 1) % NUM_SAMPLE_PERIODS);
+}
+
+static void print_cpustat(void)
+{
+	int i, group;
+	u8 tail = __this_cpu_read(cpustat_tail);
+	u64 sample_period_second = sample_period;
+
+	do_div(sample_period_second, NSEC_PER_SEC);
+
+	/*
+	 * Outputting the "watchdog" prefix on every line is redundant and not
+	 * concise, and the original alarm information is sufficient for
+	 * positioning in logs, hence here printk() is used instead of pr_crit().
+	 */
+	printk(KERN_CRIT "CPU#%d Utilization every %llus during lockup:\n",
+	       smp_processor_id(), sample_period_second);
+
+	for (i = 0; i < NUM_SAMPLE_PERIODS; i++) {
+		group = (tail + i) % NUM_SAMPLE_PERIODS;
+		printk(KERN_CRIT "\t#%d: %3u%% system,\t%3u%% softirq,\t"
+			"%3u%% hardirq,\t%3u%% idle\n", i + 1,
+			__this_cpu_read(cpustat_util[group][STATS_SYSTEM]),
+			__this_cpu_read(cpustat_util[group][STATS_SOFTIRQ]),
+			__this_cpu_read(cpustat_util[group][STATS_HARDIRQ]),
+			__this_cpu_read(cpustat_util[group][STATS_IDLE]));
+	}
+}
+
+static void report_cpu_status(void)
+{
+	print_cpustat();
+}
+#else
+static inline void update_cpustat(void) { }
+static inline void report_cpu_status(void) { }
+#endif
+
 /*
  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
  * lockups can have false positives under extreme conditions. So we generally
@@ -364,7 +458,7 @@ static void set_sample_period(void)
 	 * and hard thresholds) to increment before the
 	 * hardlockup detector generates a warning
 	 */
-	sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
+	sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / NUM_SAMPLE_PERIODS);
 	watchdog_update_hrtimer_threshold(sample_period);
 }
 
@@ -504,6 +598,8 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 	 */
 	period_ts = READ_ONCE(*this_cpu_ptr(&watchdog_report_ts));
 
+	update_cpustat();
+
 	/* Reset the interval when touched by known problematic code. */
 	if (period_ts == SOFTLOCKUP_DELAY_REPORT) {
 		if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
@@ -539,6 +635,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 		pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 			smp_processor_id(), duration,
 			current->comm, task_pid_nr(current));
+		report_cpu_status();
 		print_modules();
 		print_irqtrace_events(current);
 		if (regs)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index c63a5fbf1f1c..1f0ce712a671 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1029,6 +1029,20 @@ config SOFTLOCKUP_DETECTOR
 	  chance to run.  The current stack trace is displayed upon
 	  detection and the system will stay locked up.
 
+config SOFTLOCKUP_DETECTOR_INTR_STORM
+	bool "Detect Interrupt Storm in Soft Lockups"
+	depends on SOFTLOCKUP_DETECTOR && IRQ_TIME_ACCOUNTING
+	select GENERIC_IRQ_STAT_SNAPSHOT
+	default y if NR_CPUS <= 128
+	help
+	  Say Y here to enable the kernel to detect interrupt storm
+	  during "soft lockups".
+
+	  "soft lockups" can be caused by a variety of reasons. If one is
+	  caused by an interrupt storm, then the storming interrupts will not
+	  be on the callstack. To detect this case, it is necessary to report
+	  the CPU stats and the interrupt counts during the "soft lockups".
+
 config BOOTPARAM_SOFTLOCKUP_PANIC
 	bool "Panic (Reboot) On Soft Lockups"
 	depends on SOFTLOCKUP_DETECTOR
-- 
2.37.1 (Apple Git-137.1)

[PATCHv13 5/5] watchdog/softlockup: report the most frequent interrupts

[Bitao Hu]

When the watchdog determines that the current soft lockup is due
to an interrupt storm based on CPU utilization, reporting the
most frequent interrupts could be good enough for further
troubleshooting.

Below is an example of interrupt storm. The call tree does not
provide useful information, but we can analyze which interrupt
caused the soft lockup by comparing the counts of interrupts.

[  638.870231] watchdog: BUG: soft lockup - CPU#9 stuck for 26s! [swapper/9:0]
[  638.870825] CPU#9 Utilization every 4s during lockup:
[  638.871194]  #1:   0% system,          0% softirq,   100% hardirq,     0% idle
[  638.871652]  #2:   0% system,          0% softirq,   100% hardirq,     0% idle
[  638.872107]  #3:   0% system,          0% softirq,   100% hardirq,     0% idle
[  638.872563]  #4:   0% system,          0% softirq,   100% hardirq,     0% idle
[  638.873018]  #5:   0% system,          0% softirq,   100% hardirq,     0% idle
[  638.873494] CPU#9 Detect HardIRQ Time exceeds 50%. Most frequent HardIRQs:
[  638.873994]  #1: 330945      irq#7
[  638.874236]  #2: 31          irq#82
[  638.874493]  #3: 10          irq#10
[  638.874744]  #4: 2           irq#89
[  638.874992]  #5: 1           irq#102
...
[  638.875313] Call trace:
[  638.875315]  __do_softirq+0xa8/0x364

Signed-off-by: Bitao Hu <yaoma@linux.alibaba.com>
Reviewed-by: Liu Song <liusong@linux.alibaba.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
---
 kernel/watchdog.c | 116 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 112 insertions(+), 4 deletions(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index ef8ebd31fdab..d12ff74889ed 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -12,22 +12,25 @@
 
 #define pr_fmt(fmt) "watchdog: " fmt
 
-#include <linux/mm.h>
 #include <linux/cpu.h>
-#include <linux/nmi.h>
 #include <linux/init.h>
+#include <linux/irq.h>
+#include <linux/irqdesc.h>
 #include <linux/kernel_stat.h>
+#include <linux/kvm_para.h>
 #include <linux/math64.h>
+#include <linux/mm.h>
 #include <linux/module.h>
+#include <linux/nmi.h>
+#include <linux/stop_machine.h>
 #include <linux/sysctl.h>
 #include <linux/tick.h>
+
 #include <linux/sched/clock.h>
 #include <linux/sched/debug.h>
 #include <linux/sched/isolation.h>
-#include <linux/stop_machine.h>
 
 #include <asm/irq_regs.h>
-#include <linux/kvm_para.h>
 
 static DEFINE_MUTEX(watchdog_mutex);
 
@@ -418,13 +421,105 @@ static void print_cpustat(void)
 	}
 }
 
+#define HARDIRQ_PERCENT_THRESH          50
+#define NUM_HARDIRQ_REPORT              5
+struct irq_counts {
+	int irq;
+	u32 counts;
+};
+
+static DEFINE_PER_CPU(bool, snapshot_taken);
+
+/* Tabulate the most frequent interrupts. */
+static void tabulate_irq_count(struct irq_counts *irq_counts, int irq, u32 counts, int rank)
+{
+	int i;
+	struct irq_counts new_count = {irq, counts};
+
+	for (i = 0; i < rank; i++) {
+		if (counts > irq_counts[i].counts)
+			swap(new_count, irq_counts[i]);
+	}
+}
+
+/*
+ * If the hardirq time exceeds HARDIRQ_PERCENT_THRESH% of the sample_period,
+ * then the cause of softlockup might be interrupt storm. In this case, it
+ * would be useful to start interrupt counting.
+ */
+static bool need_counting_irqs(void)
+{
+	u8 util;
+	int tail = __this_cpu_read(cpustat_tail);
+
+	tail = (tail + NUM_HARDIRQ_REPORT - 1) % NUM_HARDIRQ_REPORT;
+	util = __this_cpu_read(cpustat_util[tail][STATS_HARDIRQ]);
+	return util > HARDIRQ_PERCENT_THRESH;
+}
+
+static void start_counting_irqs(void)
+{
+	if (!__this_cpu_read(snapshot_taken)) {
+		kstat_snapshot_irqs();
+		__this_cpu_write(snapshot_taken, true);
+	}
+}
+
+static void stop_counting_irqs(void)
+{
+	__this_cpu_write(snapshot_taken, false);
+}
+
+static void print_irq_counts(void)
+{
+	unsigned int i, count;
+	struct irq_counts irq_counts_sorted[NUM_HARDIRQ_REPORT] = {
+		{-1, 0}, {-1, 0}, {-1, 0}, {-1, 0}, {-1, 0}
+	};
+
+	if (__this_cpu_read(snapshot_taken)) {
+		for_each_active_irq(i) {
+			count = kstat_get_irq_since_snapshot(i);
+			tabulate_irq_count(irq_counts_sorted, i, count, NUM_HARDIRQ_REPORT);
+		}
+
+		/*
+		 * Outputting the "watchdog" prefix on every line is redundant and not
+		 * concise, and the original alarm information is sufficient for
+		 * positioning in logs, hence here printk() is used instead of pr_crit().
+		 */
+		printk(KERN_CRIT "CPU#%d Detect HardIRQ Time exceeds %d%%. Most frequent HardIRQs:\n",
+		       smp_processor_id(), HARDIRQ_PERCENT_THRESH);
+
+		for (i = 0; i < NUM_HARDIRQ_REPORT; i++) {
+			if (irq_counts_sorted[i].irq == -1)
+				break;
+
+			printk(KERN_CRIT "\t#%u: %-10u\tirq#%d\n",
+			       i + 1, irq_counts_sorted[i].counts,
+			       irq_counts_sorted[i].irq);
+		}
+
+		/*
+		 * If the hardirq time is less than HARDIRQ_PERCENT_THRESH% in the last
+		 * sample_period, then we suspect the interrupt storm might be subsiding.
+		 */
+		if (!need_counting_irqs())
+			stop_counting_irqs();
+	}
+}
+
 static void report_cpu_status(void)
 {
 	print_cpustat();
+	print_irq_counts();
 }
 #else
 static inline void update_cpustat(void) { }
 static inline void report_cpu_status(void) { }
+static inline bool need_counting_irqs(void) { return false; }
+static inline void start_counting_irqs(void) { }
+static inline void stop_counting_irqs(void) { }
 #endif
 
 /*
@@ -528,6 +623,18 @@ static int is_softlockup(unsigned long touch_ts,
 			 unsigned long now)
 {
 	if ((watchdog_enabled & WATCHDOG_SOFTOCKUP_ENABLED) && watchdog_thresh) {
+		/*
+		 * If period_ts has not been updated during a sample_period, then
+		 * in the subsequent few sample_periods, period_ts might also not
+		 * be updated, which could indicate a potential softlockup. In
+		 * this case, if we suspect the cause of the potential softlockup
+		 * might be interrupt storm, then we need to count the interrupts
+		 * to find which interrupt is storming.
+		 */
+		if (time_after_eq(now, period_ts + get_softlockup_thresh() / NUM_SAMPLE_PERIODS) &&
+		    need_counting_irqs())
+			start_counting_irqs();
+
 		/* Warn about unreasonable delays. */
 		if (time_after(now, period_ts + get_softlockup_thresh()))
 			return now - touch_ts;
@@ -550,6 +657,7 @@ static DEFINE_PER_CPU(struct cpu_stop_work, softlockup_stop_work);
 static int softlockup_fn(void *data)
 {
 	update_touch_ts();
+	stop_counting_irqs();
 	complete(this_cpu_ptr(&softlockup_completion));
 
 	return 0;
-- 
2.37.1 (Apple Git-137.1)