[PATCH v2 04/13] tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz subsystem

[PATCH v2 04/13] tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz subsystem

[Joel Fernandes (Google)]

For CONFIG_NO_HZ_FULL systems, the tick_do_timer_cpu cannot be offlined.
However, cpu_is_hotpluggable() still returns true for those CPUs. This causes
torture tests that do offlining to end up trying to offline this CPU causing
test failures. Such failure happens on all architectures.

Fix it by asking the opinion of the nohz subsystem on whether the CPU can
be hotplugged.

[ Apply Frederic Weisbecker feedback on refactoring tick_nohz_cpu_down(). ]

For drivers/base/ portion:
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Zhouyi Zhou <zhouzhouyi@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: rcu <rcu@vger.kernel.org>
Cc: stable@vger.kernel.org
Fixes: 2987557f52b9 ("driver-core/cpu: Expose hotpluggability to the rest of the kernel")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 drivers/base/cpu.c       |  3 ++-
 include/linux/tick.h     |  2 ++
 kernel/time/tick-sched.c | 11 ++++++++---
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 182c6122f815..c1815b9dae68 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -487,7 +487,8 @@ static const struct attribute_group *cpu_root_attr_groups[] = {
 bool cpu_is_hotpluggable(unsigned int cpu)
 {
 	struct device *dev = get_cpu_device(cpu);
-	return dev && container_of(dev, struct cpu, dev)->hotpluggable;
+	return dev && container_of(dev, struct cpu, dev)->hotpluggable
+		&& tick_nohz_cpu_hotpluggable(cpu);
 }
 EXPORT_SYMBOL_GPL(cpu_is_hotpluggable);
 
diff --git a/include/linux/tick.h b/include/linux/tick.h
index bfd571f18cfd..9459fef5b857 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -216,6 +216,7 @@ extern void tick_nohz_dep_set_signal(struct task_struct *tsk,
 				     enum tick_dep_bits bit);
 extern void tick_nohz_dep_clear_signal(struct signal_struct *signal,
 				       enum tick_dep_bits bit);
+extern bool tick_nohz_cpu_hotpluggable(unsigned int cpu);
 
 /*
  * The below are tick_nohz_[set,clear]_dep() wrappers that optimize off-cases
@@ -280,6 +281,7 @@ static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) { }
 
 static inline void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit) { }
 static inline void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit) { }
+static inline bool tick_nohz_cpu_hotpluggable(unsigned int cpu) { return true; }
 
 static inline void tick_dep_set(enum tick_dep_bits bit) { }
 static inline void tick_dep_clear(enum tick_dep_bits bit) { }
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index b0e3c9205946..68d81a4283c8 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -527,7 +527,7 @@ void __init tick_nohz_full_setup(cpumask_var_t cpumask)
 	tick_nohz_full_running = true;
 }
 
-static int tick_nohz_cpu_down(unsigned int cpu)
+bool tick_nohz_cpu_hotpluggable(unsigned int cpu)
 {
 	/*
 	 * The tick_do_timer_cpu CPU handles housekeeping duty (unbound
@@ -535,8 +535,13 @@ static int tick_nohz_cpu_down(unsigned int cpu)
 	 * CPUs. It must remain online when nohz full is enabled.
 	 */
 	if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
-		return -EBUSY;
-	return 0;
+		return false;
+	return true;
+}
+
+static int tick_nohz_cpu_down(unsigned int cpu)
+{
+	return tick_nohz_cpu_hotpluggable(cpu) ? 0 : -EBUSY;
 }
 
 void __init tick_nohz_init(void)
-- 
2.40.0.348.gf938b09366-goog

Re: [PATCH v2 04/13] tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz subsystem

[Frederic Weisbecker]

Le Sat, Mar 25, 2023 at 05:33:07PM +0000, Joel Fernandes (Google) a écrit :
> For CONFIG_NO_HZ_FULL systems, the tick_do_timer_cpu cannot be offlined.
> However, cpu_is_hotpluggable() still returns true for those CPUs. This causes
> torture tests that do offlining to end up trying to offline this CPU causing
> test failures. Such failure happens on all architectures.

It might be worth noting that hotplug failure is fine on hotplug testing.
The issue here is the repetitive error message in the logs.

Other than that:

Acked-by: Frederic Weisbecker <frederic@kernel.org>

Re: [PATCH v2 04/13] tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz subsystem

[Joel Fernandes]

On Sun, Mar 26, 2023 at 09:34:35PM +0200, Frederic Weisbecker wrote:
> Le Sat, Mar 25, 2023 at 05:33:07PM +0000, Joel Fernandes (Google) a écrit :
> > For CONFIG_NO_HZ_FULL systems, the tick_do_timer_cpu cannot be offlined.
> > However, cpu_is_hotpluggable() still returns true for those CPUs. This causes
> > torture tests that do offlining to end up trying to offline this CPU causing
> > test failures. Such failure happens on all architectures.
> 
> It might be worth noting that hotplug failure is fine on hotplug testing.
> The issue here is the repetitive error message in the logs.
> 
> Other than that:
> 
> Acked-by: Frederic Weisbecker <frederic@kernel.org>

Thank you, below is the reworded update. Let me know if any other comment.

-------8<-------

From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
Subject: [PATCH] tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz
 subsystem

For CONFIG_NO_HZ_FULL systems, the tick_do_timer_cpu cannot be offlined.
However, cpu_is_hotpluggable() still returns true for those CPUs. This causes
torture tests that do offlining to end up trying to offline this CPU causing
test failures. Such failure happens on all architectures.

Fix the repeated error messages thrown as a result (even if the hotplug
errors are harmless), by asking the opinion of the nohz subsystem on whether
the CPU can be hotplugged.

[ Apply Frederic Weisbecker feedback on refactoring tick_nohz_cpu_down(). ]

For drivers/base/ portion:
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Zhouyi Zhou <zhouzhouyi@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: rcu <rcu@vger.kernel.org>
Cc: stable@vger.kernel.org
Fixes: 2987557f52b9 ("driver-core/cpu: Expose hotpluggability to the rest of the kernel")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 drivers/base/cpu.c       |  3 ++-
 include/linux/tick.h     |  2 ++
 kernel/time/tick-sched.c | 11 ++++++++---
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 182c6122f815..c1815b9dae68 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -487,7 +487,8 @@ static const struct attribute_group *cpu_root_attr_groups[] = {
 bool cpu_is_hotpluggable(unsigned int cpu)
 {
 	struct device *dev = get_cpu_device(cpu);
-	return dev && container_of(dev, struct cpu, dev)->hotpluggable;
+	return dev && container_of(dev, struct cpu, dev)->hotpluggable
+		&& tick_nohz_cpu_hotpluggable(cpu);
 }
 EXPORT_SYMBOL_GPL(cpu_is_hotpluggable);
 
diff --git a/include/linux/tick.h b/include/linux/tick.h
index bfd571f18cfd..9459fef5b857 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -216,6 +216,7 @@ extern void tick_nohz_dep_set_signal(struct task_struct *tsk,
 				     enum tick_dep_bits bit);
 extern void tick_nohz_dep_clear_signal(struct signal_struct *signal,
 				       enum tick_dep_bits bit);
+extern bool tick_nohz_cpu_hotpluggable(unsigned int cpu);
 
 /*
  * The below are tick_nohz_[set,clear]_dep() wrappers that optimize off-cases
@@ -280,6 +281,7 @@ static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) { }
 
 static inline void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit) { }
 static inline void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit) { }
+static inline bool tick_nohz_cpu_hotpluggable(unsigned int cpu) { return true; }
 
 static inline void tick_dep_set(enum tick_dep_bits bit) { }
 static inline void tick_dep_clear(enum tick_dep_bits bit) { }
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index ba2ac1469d47..a46506f7ec6d 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -532,7 +532,7 @@ void __init tick_nohz_full_setup(cpumask_var_t cpumask)
 	tick_nohz_full_running = true;
 }
 
-static int tick_nohz_cpu_down(unsigned int cpu)
+bool tick_nohz_cpu_hotpluggable(unsigned int cpu)
 {
 	/*
 	 * The tick_do_timer_cpu CPU handles housekeeping duty (unbound
@@ -540,8 +540,13 @@ static int tick_nohz_cpu_down(unsigned int cpu)
 	 * CPUs. It must remain online when nohz full is enabled.
 	 */
 	if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
-		return -EBUSY;
-	return 0;
+		return false;
+	return true;
+}
+
+static int tick_nohz_cpu_down(unsigned int cpu)
+{
+	return tick_nohz_cpu_hotpluggable(cpu) ? 0 : -EBUSY;
 }
 
 void __init tick_nohz_init(void)
-- 
2.40.0.rc1.284.g88254d51c5-goog

[PATCH v2 12/13] rcu: Avoid stack overflow due to __rcu_irq_enter_check_tick() being kprobe-ed

[Joel Fernandes (Google)]

From: Zheng Yejian <zhengyejian1@huawei.com>

Registering a kprobe on __rcu_irq_enter_check_tick() can cause kernel
stack overflow as shown below. This issue can be reproduced by enabling
CONFIG_NO_HZ_FULL and booting the kernel with argument "nohz_full=",
and then giving the following commands at the shell prompt:

  # cd /sys/kernel/tracing/
  # echo 'p:mp1 __rcu_irq_enter_check_tick' >> kprobe_events
  # echo 1 > events/kprobes/enable

This commit therefore adds __rcu_irq_enter_check_tick() to the kprobes
blacklist using NOKPROBE_SYMBOL().

Insufficient stack space to handle exception!
ESR: 0x00000000f2000004 -- BRK (AArch64)
FAR: 0x0000ffffccf3e510
Task stack:     [0xffff80000ad30000..0xffff80000ad38000]
IRQ stack:      [0xffff800008050000..0xffff800008058000]
Overflow stack: [0xffff089c36f9f310..0xffff089c36fa0310]
CPU: 5 PID: 190 Comm: bash Not tainted 6.2.0-rc2-00320-g1f5abbd77e2c #19
Hardware name: linux,dummy-virt (DT)
pstate: 400003c5 (nZcv DAIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : __rcu_irq_enter_check_tick+0x0/0x1b8
lr : ct_nmi_enter+0x11c/0x138
sp : ffff80000ad30080
x29: ffff80000ad30080 x28: ffff089c82e20000 x27: 0000000000000000
x26: 0000000000000000 x25: ffff089c02a8d100 x24: 0000000000000000
x23: 00000000400003c5 x22: 0000ffffccf3e510 x21: ffff089c36fae148
x20: ffff80000ad30120 x19: ffffa8da8fcce148 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000 x15: ffffa8da8e44ea6c
x14: ffffa8da8e44e968 x13: ffffa8da8e03136c x12: 1fffe113804d6809
x11: ffff6113804d6809 x10: 0000000000000a60 x9 : dfff800000000000
x8 : ffff089c026b404f x7 : 00009eec7fb297f7 x6 : 0000000000000001
x5 : ffff80000ad30120 x4 : dfff800000000000 x3 : ffffa8da8e3016f4
x2 : 0000000000000003 x1 : 0000000000000000 x0 : 0000000000000000
Kernel panic - not syncing: kernel stack overflow
CPU: 5 PID: 190 Comm: bash Not tainted 6.2.0-rc2-00320-g1f5abbd77e2c #19
Hardware name: linux,dummy-virt (DT)
Call trace:
 dump_backtrace+0xf8/0x108
 show_stack+0x20/0x30
 dump_stack_lvl+0x68/0x84
 dump_stack+0x1c/0x38
 panic+0x214/0x404
 add_taint+0x0/0xf8
 panic_bad_stack+0x144/0x160
 handle_bad_stack+0x38/0x58
 __bad_stack+0x78/0x7c
 __rcu_irq_enter_check_tick+0x0/0x1b8
 arm64_enter_el1_dbg.isra.0+0x14/0x20
 el1_dbg+0x2c/0x90
 el1h_64_sync_handler+0xcc/0xe8
 el1h_64_sync+0x64/0x68
 __rcu_irq_enter_check_tick+0x0/0x1b8
 arm64_enter_el1_dbg.isra.0+0x14/0x20
 el1_dbg+0x2c/0x90
 el1h_64_sync_handler+0xcc/0xe8
 el1h_64_sync+0x64/0x68
 __rcu_irq_enter_check_tick+0x0/0x1b8
 arm64_enter_el1_dbg.isra.0+0x14/0x20
 el1_dbg+0x2c/0x90
 el1h_64_sync_handler+0xcc/0xe8
 el1h_64_sync+0x64/0x68
 __rcu_irq_enter_check_tick+0x0/0x1b8
 [...]
 el1_dbg+0x2c/0x90
 el1h_64_sync_handler+0xcc/0xe8
 el1h_64_sync+0x64/0x68
 __rcu_irq_enter_check_tick+0x0/0x1b8
 arm64_enter_el1_dbg.isra.0+0x14/0x20
 el1_dbg+0x2c/0x90
 el1h_64_sync_handler+0xcc/0xe8
 el1h_64_sync+0x64/0x68
 __rcu_irq_enter_check_tick+0x0/0x1b8
 arm64_enter_el1_dbg.isra.0+0x14/0x20
 el1_dbg+0x2c/0x90
 el1h_64_sync_handler+0xcc/0xe8
 el1h_64_sync+0x64/0x68
 __rcu_irq_enter_check_tick+0x0/0x1b8
 el1_interrupt+0x28/0x60
 el1h_64_irq_handler+0x18/0x28
 el1h_64_irq+0x64/0x68
 __ftrace_set_clr_event_nolock+0x98/0x198
 __ftrace_set_clr_event+0x58/0x80
 system_enable_write+0x144/0x178
 vfs_write+0x174/0x738
 ksys_write+0xd0/0x188
 __arm64_sys_write+0x4c/0x60
 invoke_syscall+0x64/0x180
 el0_svc_common.constprop.0+0x84/0x160
 do_el0_svc+0x48/0xe8
 el0_svc+0x34/0xd0
 el0t_64_sync_handler+0xb8/0xc0
 el0t_64_sync+0x190/0x194
SMP: stopping secondary CPUs
Kernel Offset: 0x28da86000000 from 0xffff800008000000
PHYS_OFFSET: 0xfffff76600000000
CPU features: 0x00000,01a00100,0000421b
Memory Limit: none

Link: https://lore.kernel.org/all/20221119040049.795065-1-zhengyejian1@huawei.com/
Fixes: aaf2bc50df1f ("rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter()")
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 kernel/rcu/tree.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 90d54571126a..ee27a03d7576 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -640,6 +640,7 @@ void __rcu_irq_enter_check_tick(void)
 	}
 	raw_spin_unlock_rcu_node(rdp->mynode);
 }
+NOKPROBE_SYMBOL(__rcu_irq_enter_check_tick);
 #endif /* CONFIG_NO_HZ_FULL */
 
 /*
-- 
2.40.0.348.gf938b09366-goog