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Message-Id: <20250205032438.14668-1-laoar.shao@gmail.com>
Date: Wed, 5 Feb 2025 11:24:38 +0800
From: Yafang Shao <laoar.shao@...il.com>
To: peterz@...radead.org,
vincent.guittot@...aro.org,
dan.carpenter@...aro.org,
seanjc@...gle.com,
mkoutny@...e.com
Cc: kvm@...r.kernel.org,
linux-kernel@...r.kernel.org,
Yafang Shao <laoar.shao@...il.com>
Subject: [PATCH v2] sched: Don't define sched_clock_irqtime as static key
The sched_clock_irqtime was defined as a static key in commit 8722903cbb8f
('sched: Define sched_clock_irqtime as static key'). However, this change
introduces a 'sleeping in atomic context' warning, as shown below:
arch/x86/kernel/tsc.c:1214 mark_tsc_unstable()
warn: sleeping in atomic context
As analyzed by Dan, the affected code path is as follows:
vcpu_load() <- disables preempt
-> kvm_arch_vcpu_load()
-> mark_tsc_unstable() <- sleeps
virt/kvm/kvm_main.c
166 void vcpu_load(struct kvm_vcpu *vcpu)
167 {
168 int cpu = get_cpu();
^^^^^^^^^^
This get_cpu() disables preemption.
169
170 __this_cpu_write(kvm_running_vcpu, vcpu);
171 preempt_notifier_register(&vcpu->preempt_notifier);
172 kvm_arch_vcpu_load(vcpu, cpu);
173 put_cpu();
174 }
arch/x86/kvm/x86.c
4979 if (unlikely(vcpu->cpu != cpu) || kvm_check_tsc_unstable()) {
4980 s64 tsc_delta = !vcpu->arch.last_host_tsc ? 0 :
4981 rdtsc() - vcpu->arch.last_host_tsc;
4982 if (tsc_delta < 0)
4983 mark_tsc_unstable("KVM discovered backwards TSC");
arch/x86/kernel/tsc.c
1206 void mark_tsc_unstable(char *reason)
1207 {
1208 if (tsc_unstable)
1209 return;
1210
1211 tsc_unstable = 1;
1212 if (using_native_sched_clock())
1213 clear_sched_clock_stable();
--> 1214 disable_sched_clock_irqtime();
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
kernel/jump_label.c
245 void static_key_disable(struct static_key *key)
246 {
247 cpus_read_lock();
^^^^^^^^^^^^^^^^
This lock has a might_sleep() in it which triggers the static checker
warning.
248 static_key_disable_cpuslocked(key);
249 cpus_read_unlock();
250 }
Let revert this change for now as {disable,enable}_sched_clock_irqtime
are used in many places, as pointed out by Sean, including the following:
The code path in clocksource_watchdog():
clocksource_watchdog()
|
-> spin_lock(&watchdog_lock);
|
-> __clocksource_unstable()
|
-> clocksource.mark_unstable() == tsc_cs_mark_unstable()
|
-> disable_sched_clock_irqtime()
And the code path in sched_clock_register():
/* Cannot register a sched_clock with interrupts on */
local_irq_save(flags);
...
/* Enable IRQ time accounting if we have a fast enough sched_clock() */
if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
enable_sched_clock_irqtime();
local_irq_restore(flags);
[lkp@...el.com: reported a build error in the prev version]
Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
Closes: https://lore.kernel.org/kvm/37a79ba3-9ce0-479c-a5b0-2bd75d573ed3@stanley.mountain/
Debugged-by: Dan Carpenter <dan.carpenter@...aro.org>
Debugged-by: Sean Christopherson <seanjc@...gle.com>
Debugged-by: Michal Koutný <mkoutny@...e.com>
Fixes: 8722903cbb8f ("sched: Define sched_clock_irqtime as static key")
Signed-off-by: Yafang Shao <laoar.shao@...il.com>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Sean Christopherson <seanjc@...gle.com>
Cc: Michal Koutný <mkoutny@...e.com>
Cc: Peter Zijlstra" <peterz@...radead.org>
---
kernel/sched/cputime.c | 8 ++++----
kernel/sched/sched.h | 4 ++--
2 files changed, 6 insertions(+), 6 deletions(-)
v1->v2: Fix a build error reported by kernel test robot
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 5d9143dd0879..6dab4854c6c0 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -9,8 +9,6 @@
#ifdef CONFIG_IRQ_TIME_ACCOUNTING
-DEFINE_STATIC_KEY_FALSE(sched_clock_irqtime);
-
/*
* There are no locks covering percpu hardirq/softirq time.
* They are only modified in vtime_account, on corresponding CPU
@@ -24,14 +22,16 @@ DEFINE_STATIC_KEY_FALSE(sched_clock_irqtime);
*/
DEFINE_PER_CPU(struct irqtime, cpu_irqtime);
+int sched_clock_irqtime;
+
void enable_sched_clock_irqtime(void)
{
- static_branch_enable(&sched_clock_irqtime);
+ sched_clock_irqtime = 1;
}
void disable_sched_clock_irqtime(void)
{
- static_branch_disable(&sched_clock_irqtime);
+ sched_clock_irqtime = 0;
}
static void irqtime_account_delta(struct irqtime *irqtime, u64 delta,
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 38e0e323dda2..ab16d3d0e51c 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3259,11 +3259,11 @@ struct irqtime {
};
DECLARE_PER_CPU(struct irqtime, cpu_irqtime);
-DECLARE_STATIC_KEY_FALSE(sched_clock_irqtime);
+extern int sched_clock_irqtime;
static inline int irqtime_enabled(void)
{
- return static_branch_likely(&sched_clock_irqtime);
+ return sched_clock_irqtime;
}
/*
--
2.43.5
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