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From: Sean Christopherson To: Dan Carpenter Cc: kvm@vger.kernel.org, Yafang Shao , Peter Zijlstra , "Michal =?utf-8?Q?Koutn=C3=BD?=" , Vincent Guittot Content-Type: text/plain; charset="us-ascii" +sched folks On Fri, Jan 17, 2025, Dan Carpenter wrote: > I don't know why I'm seeing this static checker warning only now. All > this code looks to be about 15 years old... > > Commit e48672fa25e8 ("KVM: x86: Unify TSC logic") from Aug 19, 2010 > (linux-next), leads to the following Smatch static checker warning: That's not the problematic commit. This popped because commit 8722903cbb8f ("sched: Define sched_clock_irqtime as static key") in the tip tree turned sched_clock_irqtime into a static key (it was a simple "int"). https://lore.kernel.org/all/20250103022409.2544-2-laoar.shao@gmail.com > arch/x86/kernel/tsc.c:1214 mark_tsc_unstable() > warn: sleeping in atomic context > > The code path is: > > 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"); > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > It seems pretty unlikely that we'll get a backwards tsc. TSC will go "backwards" if the host is suspended, in which case host TSC gets reset to 0. > 1215 pr_info("Marking TSC unstable due to %s\n", reason); > 1216 > 1217 clocksource_mark_unstable(&clocksource_tsc_early); > 1218 clocksource_mark_unstable(&clocksource_tsc); > 1219 } > > 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 } > > regards, > dan carpenter