[PATCH rcu 0/6] RCU CPU stall-warning updates for v6.3

[PATCH rcu 0/6] RCU CPU stall-warning updates for v6.3

[Paul E. McKenney]

Hello!

This series contains RCU CPU stall-warning updates:

1.	Fix the return type of kstat_cpu_irqs_sum(), courtesy of Zhen Lei.

2.	Add helper kstat_cpu_softirqs_sum(), courtesy of Zhen Lei.

3.	Add helper nr_context_switches_cpu(), courtesy of Zhen Lei.

4.	Add RCU stall diagnosis information, courtesy of Zhen Lei.

5.	Align the output of RCU CPU stall warning messages, courtesy of
	Zhen Lei.

6.	Allow up to five minutes expedited RCU CPU stall-warning timeouts.

						Thanx, Paul

------------------------------------------------------------------------

 b/Documentation/admin-guide/kernel-parameters.txt |    6 ++++
 b/include/linux/kernel_stat.h                     |    2 -
 b/kernel/rcu/Kconfig.debug                        |   13 +++++++++
 b/kernel/rcu/rcu.h                                |    1 
 b/kernel/rcu/tree.c                               |   18 ++++++++++++
 b/kernel/rcu/tree.h                               |   19 +++++++++++++
 b/kernel/rcu/tree_stall.h                         |   31 ++++++++++++++++++++++
 b/kernel/rcu/update.c                             |    2 +
 b/kernel/sched/core.c                             |    5 +++
 include/linux/kernel_stat.h                       |   12 ++++++++
 kernel/rcu/Kconfig.debug                          |    2 -
 kernel/rcu/tree_stall.h                           |    6 ++--
 12 files changed, 112 insertions(+), 5 deletions(-)

[PATCH rcu 1/6] genirq: Fix the return type of kstat_cpu_irqs_sum()

[Paul E. McKenney]

From: Zhen Lei <thunder.leizhen@huawei.com>

The type of member ->irqs_sum is unsigned long, but kstat_cpu_irqs_sum()
returns int, which can result in truncation.  Therefore, change the
kstat_cpu_irqs_sum() function's return value to unsigned long to avoid
truncation.

Fixes: f2c66cd8eedd ("/proc/stat: scalability of irq num per cpu")
Reported-by: Elliott, Robert (Servers) <elliott@hpe.com>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Josh Don <joshdon@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/kernel_stat.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h
index ddb5a358fd829..90e2fdc17d79f 100644
--- a/include/linux/kernel_stat.h
+++ b/include/linux/kernel_stat.h
@@ -75,7 +75,7 @@ extern unsigned int kstat_irqs_usr(unsigned int irq);
 /*
  * Number of interrupts per cpu, since bootup
  */
-static inline unsigned int kstat_cpu_irqs_sum(unsigned int cpu)
+static inline unsigned long kstat_cpu_irqs_sum(unsigned int cpu)
 {
 	return kstat_cpu(cpu).irqs_sum;
 }
-- 
2.31.1.189.g2e36527f23

[PATCH rcu 2/6] sched: Add helper kstat_cpu_softirqs_sum()

[Paul E. McKenney]

From: Zhen Lei <thunder.leizhen@huawei.com>

Add a kstat_cpu_softirqs_sum() function that is similar to
kstat_cpu_irqs_sum(), but which counts software interrupts since boot
on the specified CPU.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Cc: Josh Don <joshdon@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/kernel_stat.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h
index 90e2fdc17d79f..898076e173a92 100644
--- a/include/linux/kernel_stat.h
+++ b/include/linux/kernel_stat.h
@@ -67,6 +67,17 @@ static inline unsigned int kstat_softirqs_cpu(unsigned int irq, int cpu)
        return kstat_cpu(cpu).softirqs[irq];
 }
 
+static inline unsigned int kstat_cpu_softirqs_sum(int cpu)
+{
+	int i;
+	unsigned int sum = 0;
+
+	for (i = 0; i < NR_SOFTIRQS; i++)
+		sum += kstat_softirqs_cpu(i, cpu);
+
+	return sum;
+}
+
 /*
  * Number of interrupts per specific IRQ source, since bootup
  */
-- 
2.31.1.189.g2e36527f23

[PATCH rcu 3/6] sched: Add helper nr_context_switches_cpu()

[Paul E. McKenney]

From: Zhen Lei <thunder.leizhen@huawei.com>

Add a function nr_context_switches_cpu() that returns  number of context
switches since boot on the specified CPU.  This information will be used
to diagnose RCU CPU stalls.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/kernel_stat.h | 1 +
 kernel/sched/core.c         | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h
index 898076e173a92..9935f7ecbfb9e 100644
--- a/include/linux/kernel_stat.h
+++ b/include/linux/kernel_stat.h
@@ -52,6 +52,7 @@ DECLARE_PER_CPU(struct kernel_cpustat, kernel_cpustat);
 #define kstat_cpu(cpu) per_cpu(kstat, cpu)
 #define kcpustat_cpu(cpu) per_cpu(kernel_cpustat, cpu)
 
+extern unsigned long long nr_context_switches_cpu(int cpu);
 extern unsigned long long nr_context_switches(void);
 
 extern unsigned int kstat_irqs_cpu(unsigned int irq, int cpu);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 25b582b6ee5f7..2e40a6c116e1c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5282,6 +5282,11 @@ bool single_task_running(void)
 }
 EXPORT_SYMBOL(single_task_running);
 
+unsigned long long nr_context_switches_cpu(int cpu)
+{
+	return cpu_rq(cpu)->nr_switches;
+}
+
 unsigned long long nr_context_switches(void)
 {
 	int i;
-- 
2.31.1.189.g2e36527f23

[PATCH rcu 4/6] rcu: Add RCU stall diagnosis information

[Paul E. McKenney]

From: Zhen Lei <thunder.leizhen@huawei.com>

Because RCU CPU stall warnings are driven from the scheduling-clock
interrupt handler, a workload consisting of a very large number of
short-duration hardware interrupts can result in misleading stall-warning
messages.  On systems supporting only a single level of interrupts,
that is, where interrupts handlers cannot be interrupted, this can
produce misleading diagnostics.  The stack traces will show the
innocent-bystander interrupted task, not the interrupts that are
at the very least exacerbating the stall.

This situation can be improved by displaying the number of interrupts
and the CPU time that they have consumed.  Diagnosing other types
of stalls can be eased by also providing the count of softirqs and
the CPU time that they consumed as well as the number of context
switches and the task-level CPU time consumed.

Consider the following output given this change:

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu:     0-....: (1250 ticks this GP) <omitted>
rcu:          hardirqs   softirqs   csw/system
rcu:  number:      624         45            0
rcu: cputime:       69          1         2425   ==> 2500(ms)

This output shows that the number of hard and soft interrupts is small,
there are no context switches, and the system takes up a lot of time. This
indicates that the current task is looping with preemption disabled.

The impact on system performance is negligible because snapshot is
recorded only once for all continuous RCU stalls.

This added debugging information is suppressed by default and can be
enabled by building the kernel with CONFIG_RCU_CPU_STALL_CPUTIME=y or
by booting with rcupdate.rcu_cpu_stall_cputime=1.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Mukesh Ojha <quic_mojha@quicinc.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 .../admin-guide/kernel-parameters.txt         |  6 ++++
 kernel/rcu/Kconfig.debug                      | 13 ++++++++
 kernel/rcu/rcu.h                              |  1 +
 kernel/rcu/tree.c                             | 18 +++++++++++
 kernel/rcu/tree.h                             | 19 ++++++++++++
 kernel/rcu/tree_stall.h                       | 31 +++++++++++++++++++
 kernel/rcu/update.c                           |  2 ++
 7 files changed, 90 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 6cfa6e3996cf7..43ca7f3ac96a1 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5113,6 +5113,12 @@
 			rcupdate.rcu_cpu_stall_timeout to be used (after
 			conversion from seconds to milliseconds).
 
+	rcupdate.rcu_cpu_stall_cputime= [KNL]
+			Provide statistics on the cputime and count of
+			interrupts and tasks during the sampling period. For
+			multiple continuous RCU stalls, all sampling periods
+			begin at half of the first RCU stall timeout.
+
 	rcupdate.rcu_expedited= [KNL]
 			Use expedited grace-period primitives, for
 			example, synchronize_rcu_expedited() instead
diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 232e29fe3e5ec..49da904df6aa6 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -92,6 +92,19 @@ config RCU_EXP_CPU_STALL_TIMEOUT
 	  says to use the RCU_CPU_STALL_TIMEOUT value converted from
 	  seconds to milliseconds.
 
+config RCU_CPU_STALL_CPUTIME
+	bool "Provide additional RCU stall debug information"
+	depends on RCU_STALL_COMMON
+	default n
+	help
+	  Collect statistics during the sampling period, such as the number of
+	  (hard interrupts, soft interrupts, task switches) and the cputime of
+	  (hard interrupts, soft interrupts, kernel tasks) are added to the
+	  RCU stall report. For multiple continuous RCU stalls, all sampling
+	  periods begin at half of the first RCU stall timeout.
+	  The boot option rcupdate.rcu_cpu_stall_cputime has the same function
+	  as this one, but will override this if it exists.
+
 config RCU_TRACE
 	bool "Enable tracing for RCU"
 	depends on DEBUG_KERNEL
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index c5aa934de59b0..ff35920e1055e 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -224,6 +224,7 @@ extern int rcu_cpu_stall_ftrace_dump;
 extern int rcu_cpu_stall_suppress;
 extern int rcu_cpu_stall_timeout;
 extern int rcu_exp_cpu_stall_timeout;
+extern int rcu_cpu_stall_cputime;
 int rcu_jiffies_till_stall_check(void);
 int rcu_exp_jiffies_till_stall_check(void);
 
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index cf34a961821ad..65552e6a6a5d2 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -925,6 +925,24 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 			rdp->rcu_iw_gp_seq = rnp->gp_seq;
 			irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
 		}
+
+		if (rcu_cpu_stall_cputime && rdp->snap_record.gp_seq != rdp->gp_seq) {
+			int cpu = rdp->cpu;
+			struct rcu_snap_record *rsrp;
+			struct kernel_cpustat *kcsp;
+
+			kcsp = &kcpustat_cpu(cpu);
+
+			rsrp = &rdp->snap_record;
+			rsrp->cputime_irq     = kcpustat_field(kcsp, CPUTIME_IRQ, cpu);
+			rsrp->cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu);
+			rsrp->cputime_system  = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu);
+			rsrp->nr_hardirqs = kstat_cpu_irqs_sum(rdp->cpu);
+			rsrp->nr_softirqs = kstat_cpu_softirqs_sum(rdp->cpu);
+			rsrp->nr_csw = nr_context_switches_cpu(rdp->cpu);
+			rsrp->jiffies = jiffies;
+			rsrp->gp_seq = rdp->gp_seq;
+		}
 	}
 
 	return 0;
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index fcb5d696eb170..192536916f9a6 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -158,6 +158,23 @@ union rcu_noqs {
 	u16 s; /* Set of bits, aggregate OR here. */
 };
 
+/*
+ * Record the snapshot of the core stats at half of the first RCU stall timeout.
+ * The member gp_seq is used to ensure that all members are updated only once
+ * during the sampling period. The snapshot is taken only if this gp_seq is not
+ * equal to rdp->gp_seq.
+ */
+struct rcu_snap_record {
+	unsigned long	gp_seq;		/* Track rdp->gp_seq counter */
+	u64		cputime_irq;	/* Accumulated cputime of hard irqs */
+	u64		cputime_softirq;/* Accumulated cputime of soft irqs */
+	u64		cputime_system; /* Accumulated cputime of kernel tasks */
+	unsigned long	nr_hardirqs;	/* Accumulated number of hard irqs */
+	unsigned int	nr_softirqs;	/* Accumulated number of soft irqs */
+	unsigned long long nr_csw;	/* Accumulated number of task switches */
+	unsigned long   jiffies;	/* Track jiffies value */
+};
+
 /* Per-CPU data for read-copy update. */
 struct rcu_data {
 	/* 1) quiescent-state and grace-period handling : */
@@ -262,6 +279,8 @@ struct rcu_data {
 	short rcu_onl_gp_flags;		/* ->gp_flags at last online. */
 	unsigned long last_fqs_resched;	/* Time of last rcu_resched(). */
 	unsigned long last_sched_clock;	/* Jiffies of last rcu_sched_clock_irq(). */
+	struct rcu_snap_record snap_record; /* Snapshot of core stats at half of */
+					    /* the first RCU stall timeout */
 
 	long lazy_len;			/* Length of buffered lazy callbacks. */
 	int cpu;
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 5653560573e22..6de15fb10bc47 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -428,6 +428,35 @@ static bool rcu_is_rcuc_kthread_starving(struct rcu_data *rdp, unsigned long *jp
 	return j > 2 * HZ;
 }
 
+static void print_cpu_stat_info(int cpu)
+{
+	struct rcu_snap_record rsr, *rsrp;
+	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+	struct kernel_cpustat *kcsp = &kcpustat_cpu(cpu);
+
+	if (!rcu_cpu_stall_cputime)
+		return;
+
+	rsrp = &rdp->snap_record;
+	if (rsrp->gp_seq != rdp->gp_seq)
+		return;
+
+	rsr.cputime_irq     = kcpustat_field(kcsp, CPUTIME_IRQ, cpu);
+	rsr.cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu);
+	rsr.cputime_system  = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu);
+
+	pr_err("\t         hardirqs   softirqs   csw/system\n");
+	pr_err("\t number: %8ld %10d %12lld\n",
+		kstat_cpu_irqs_sum(cpu) - rsrp->nr_hardirqs,
+		kstat_cpu_softirqs_sum(cpu) - rsrp->nr_softirqs,
+		nr_context_switches_cpu(cpu) - rsrp->nr_csw);
+	pr_err("\tcputime: %8lld %10lld %12lld   ==> %d(ms)\n",
+		div_u64(rsr.cputime_irq - rsrp->cputime_irq, NSEC_PER_MSEC),
+		div_u64(rsr.cputime_softirq - rsrp->cputime_softirq, NSEC_PER_MSEC),
+		div_u64(rsr.cputime_system - rsrp->cputime_system, NSEC_PER_MSEC),
+		jiffies_to_msecs(jiffies - rsrp->jiffies));
+}
+
 /*
  * Print out diagnostic information for the specified stalled CPU.
  *
@@ -484,6 +513,8 @@ static void print_cpu_stall_info(int cpu)
 	       data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,
 	       rcuc_starved ? buf : "",
 	       falsepositive ? " (false positive?)" : "");
+
+	print_cpu_stat_info(cpu);
 }
 
 /* Complain about starvation of grace-period kthread.  */
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index f5e6a2f95a2a0..8d72cb7caeadf 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -508,6 +508,8 @@ int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
 module_param(rcu_cpu_stall_timeout, int, 0644);
 int rcu_exp_cpu_stall_timeout __read_mostly = CONFIG_RCU_EXP_CPU_STALL_TIMEOUT;
 module_param(rcu_exp_cpu_stall_timeout, int, 0644);
+int rcu_cpu_stall_cputime __read_mostly = IS_ENABLED(CONFIG_RCU_CPU_STALL_CPUTIME);
+module_param(rcu_cpu_stall_cputime, int, 0644);
 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */
 
 // Suppress boot-time RCU CPU stall warnings and rcutorture writer stall
-- 
2.31.1.189.g2e36527f23

[PATCH rcu 5/6] rcu: Align the output of RCU CPU stall warning messages

[Paul E. McKenney]

From: Zhen Lei <thunder.leizhen@huawei.com>

Time stamps are added to the output in kernels built with
CONFIG_PRINTK_TIME=y, which causes misaligned output.  Therefore,
replace pr_cont() with pr_err(), which fixes alignment and gets
rid of a couple of despised pr_cont() calls.

Before:
[   37.567343] rcu: INFO: rcu_preempt self-detected stall on CPU
[   37.567839] rcu:     0-....: (1500 ticks this GP) idle=***
[   37.568270]  (t=1501 jiffies g=4717 q=28 ncpus=4)
[   37.568668] CPU: 0 PID: 313 Comm: test0 Not tainted 6.1.0-rc4 #8

After:
[   36.762074] rcu: INFO: rcu_preempt self-detected stall on CPU
[   36.762543] rcu:     0-....: (1499 ticks this GP) idle=***
[   36.763003] rcu:     (t=1500 jiffies g=5097 q=27 ncpus=4)
[   36.763522] CPU: 0 PID: 313 Comm: test0 Not tainted 6.1.0-rc4 #9

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree_stall.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 6de15fb10bc47..f360894f5599d 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -619,7 +619,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 
 	for_each_possible_cpu(cpu)
 		totqlen += rcu_get_n_cbs_cpu(cpu);
-	pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu ncpus=%d)\n",
+	pr_err("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu ncpus=%d)\n",
 	       smp_processor_id(), (long)(jiffies - gps),
 	       (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, rcu_state.n_online_cpus);
 	if (ndetected) {
@@ -680,7 +680,7 @@ static void print_cpu_stall(unsigned long gps)
 	raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
 	for_each_possible_cpu(cpu)
 		totqlen += rcu_get_n_cbs_cpu(cpu);
-	pr_cont("\t(t=%lu jiffies g=%ld q=%lu ncpus=%d)\n",
+	pr_err("\t(t=%lu jiffies g=%ld q=%lu ncpus=%d)\n",
 		jiffies - gps,
 		(long)rcu_seq_current(&rcu_state.gp_seq), totqlen, rcu_state.n_online_cpus);
 
-- 
2.31.1.189.g2e36527f23

[PATCH rcu 6/6] rcu: Allow up to five minutes expedited RCU CPU stall-warning timeouts

[Paul E. McKenney]

The maximum value of RCU CPU stall-warning timeouts has historically been
five minutes (300 seconds).  However, the recently introduced expedited
RCU CPU stall-warning timeout is instead limited to 21 seconds.  This
causes problems for CI/fuzzing services such as syzkaller by obscuring
the issue in question with expedited RCU CPU stall-warning timeout splats.

This commit therefore sets the RCU_EXP_CPU_STALL_TIMEOUT Kconfig options
upper bound to 300000 milliseconds, which is 300 seconds and 5 minutes.

[ paulmck: Apply feedback from Hillf Danton. ]

Reported-by: Dave Chinner <david@fromorbit.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/Kconfig.debug | 2 +-
 kernel/rcu/tree_stall.h  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 49da904df6aa6..2984de629f749 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -82,7 +82,7 @@ config RCU_CPU_STALL_TIMEOUT
 config RCU_EXP_CPU_STALL_TIMEOUT
 	int "Expedited RCU CPU stall timeout in milliseconds"
 	depends on RCU_STALL_COMMON
-	range 0 21000
+	range 0 300000
 	default 0
 	help
 	  If a given expedited RCU grace period extends more than the
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index f360894f5599d..b10b8349bb2a4 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -39,7 +39,7 @@ int rcu_exp_jiffies_till_stall_check(void)
 	// CONFIG_RCU_EXP_CPU_STALL_TIMEOUT, so check the allowed range.
 	// The minimum clamped value is "2UL", because at least one full
 	// tick has to be guaranteed.
-	till_stall_check = clamp(msecs_to_jiffies(cpu_stall_timeout), 2UL, 21UL * HZ);
+	till_stall_check = clamp(msecs_to_jiffies(cpu_stall_timeout), 2UL, 300UL * HZ);
 
 	if (cpu_stall_timeout && jiffies_to_msecs(till_stall_check) != cpu_stall_timeout)
 		WRITE_ONCE(rcu_exp_cpu_stall_timeout, jiffies_to_msecs(till_stall_check));
-- 
2.31.1.189.g2e36527f23

Re: [PATCH rcu 6/6] rcu: Allow up to five minutes expedited RCU CPU stall-warning timeouts

[Geert Uytterhoeven]

Hi Paul,

Thanks for your patch, which is now commit 0d49d9123dcf41f7 ("rcu:
Allow up to five minutes expedited RCU CPU stall-warning timeouts")
in next-20230109.

On Thu, Jan 5, 2023 at 2:10 AM Paul E. McKenney <paulmck@kernel.org> wrote:
> The maximum value of RCU CPU stall-warning timeouts has historically been
> five minutes (300 seconds).  However, the recently introduced expedited
> RCU CPU stall-warning timeout is instead limited to 21 seconds.  This
> causes problems for CI/fuzzing services such as syzkaller by obscuring
> the issue in question with expedited RCU CPU stall-warning timeout splats.
>
> This commit therefore sets the RCU_EXP_CPU_STALL_TIMEOUT Kconfig options
> upper bound to 300000 milliseconds, which is 300 seconds and 5 minutes.

s/and/or/

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH rcu 6/6] rcu: Allow up to five minutes expedited RCU CPU stall-warning timeouts

[Paul E. McKenney]

On Mon, Jan 09, 2023 at 11:10:10AM +0100, Geert Uytterhoeven wrote:
> Hi Paul,
> 
> Thanks for your patch, which is now commit 0d49d9123dcf41f7 ("rcu:
> Allow up to five minutes expedited RCU CPU stall-warning timeouts")
> in next-20230109.
> 
> On Thu, Jan 5, 2023 at 2:10 AM Paul E. McKenney <paulmck@kernel.org> wrote:
> > The maximum value of RCU CPU stall-warning timeouts has historically been
> > five minutes (300 seconds).  However, the recently introduced expedited
> > RCU CPU stall-warning timeout is instead limited to 21 seconds.  This
> > causes problems for CI/fuzzing services such as syzkaller by obscuring
> > the issue in question with expedited RCU CPU stall-warning timeout splats.
> >
> > This commit therefore sets the RCU_EXP_CPU_STALL_TIMEOUT Kconfig options
> > upper bound to 300000 milliseconds, which is 300 seconds and 5 minutes.
> 
> s/and/or/

Good eyes!  I will apply with attribution on my next rebase.

							Thanx, Paul