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Sat, 25 Jan 2025 22:50:43 -0800 (PST) From: Yafang Shao To: dan.carpenter@linaro.org, seanjc@google.com, mkoutny@suse.com, vincent.guittot@linaro.org, peterz@infradead.org Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Yafang Shao Subject: [PATCH] sched: Don't define sched_clock_irqtime as static key Date: Sun, 26 Jan 2025 14:50:37 +0800 Message-Id: <20250126065037.97935-1-laoar.shao@gmail.com> X-Mailer: git-send-email 2.37.1 (Apple Git-137.1) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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); Reported-by: Dan Carpenter Closes: https://lore.kernel.org/kvm/37a79ba3-9ce0-479c-a5b0-2bd75d573ed3@stanley.mountain/ Debugged-by: Dan Carpenter Debugged-by: Sean Christopherson Debugged-by: Michal Koutný Fixes: 8722903cbb8f ("sched: Define sched_clock_irqtime as static key") Signed-off-by: Yafang Shao Cc: Dan Carpenter Cc: Sean Christopherson Cc: Michal Koutný Cc: Peter Zijlstra" Cc: Vincent Guittot" Reviewed-by: Vincent Guittot --- kernel/sched/cputime.c | 8 ++++---- kernel/sched/sched.h | 4 ++-- 2 files changed, 6 insertions(+), 6 deletions(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 5d9143dd0879..c7904ce2345a 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); +static 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; } /*