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![Breno Leitao](/assets/img/avatar_default.png)
When booting a pseries kernel with PREEMPT enabled, it dumps the following warning: BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1 caller is pseries_processor_idle_init+0x5c/0x22c CPU: 13 PID: 1 Comm: swapper/0 Not tainted 4.20.0-rc3-00090-g12201a0128bc-dirty #828 Call Trace: [c000000429437ab0] [c0000000009c8878] dump_stack+0xec/0x164 (unreliable) [c000000429437b00] [c0000000005f2f24] check_preemption_disabled+0x154/0x160 [c000000429437b90] [c000000000cab8e8] pseries_processor_idle_init+0x5c/0x22c [c000000429437c10] [c000000000010ed4] do_one_initcall+0x64/0x300 [c000000429437ce0] [c000000000c54500] kernel_init_freeable+0x3f0/0x500 [c000000429437db0] [c0000000000112dc] kernel_init+0x2c/0x160 [c000000429437e20] [c00000000000c1d0] ret_from_kernel_thread+0x5c/0x6c This happens because the code calls get_lppaca() which calls get_paca() and it checks if preemption is disabled through check_preemption_disabled(). Preemption should be disabled because the per CPU variable may make no sense if there is a preemption (and a CPU switch) after it reads the per CPU data and when it is used. In this device driver specifically, it is not a problem, because this code just needs to have access to one lppaca struct, and it does not matter if it is the current per CPU lppaca struct or not (i.e. when there is a preemption and a CPU migration). That said, the most appropriate fix seems to be related to avoiding the debug_smp_processor_id() call at get_paca(), instead of calling preempt_disable() before get_paca(). Signed-off-by: Breno Leitao <leitao@debian.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
301 lines
6.7 KiB
C
301 lines
6.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* cpuidle-pseries - idle state cpuidle driver.
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* Adapted from drivers/idle/intel_idle.c and
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* drivers/acpi/processor_idle.c
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*
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/moduleparam.h>
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#include <linux/cpuidle.h>
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#include <linux/cpu.h>
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#include <linux/notifier.h>
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#include <asm/paca.h>
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#include <asm/reg.h>
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#include <asm/machdep.h>
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#include <asm/firmware.h>
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#include <asm/runlatch.h>
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#include <asm/plpar_wrappers.h>
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struct cpuidle_driver pseries_idle_driver = {
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.name = "pseries_idle",
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.owner = THIS_MODULE,
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};
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static int max_idle_state __read_mostly;
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static struct cpuidle_state *cpuidle_state_table __read_mostly;
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static u64 snooze_timeout __read_mostly;
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static bool snooze_timeout_en __read_mostly;
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static inline void idle_loop_prolog(unsigned long *in_purr)
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{
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ppc64_runlatch_off();
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*in_purr = mfspr(SPRN_PURR);
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/*
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* Indicate to the HV that we are idle. Now would be
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* a good time to find other work to dispatch.
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*/
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get_lppaca()->idle = 1;
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}
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static inline void idle_loop_epilog(unsigned long in_purr)
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{
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u64 wait_cycles;
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wait_cycles = be64_to_cpu(get_lppaca()->wait_state_cycles);
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wait_cycles += mfspr(SPRN_PURR) - in_purr;
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get_lppaca()->wait_state_cycles = cpu_to_be64(wait_cycles);
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get_lppaca()->idle = 0;
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ppc64_runlatch_on();
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}
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static int snooze_loop(struct cpuidle_device *dev,
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struct cpuidle_driver *drv,
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int index)
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{
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unsigned long in_purr;
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u64 snooze_exit_time;
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set_thread_flag(TIF_POLLING_NRFLAG);
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idle_loop_prolog(&in_purr);
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local_irq_enable();
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snooze_exit_time = get_tb() + snooze_timeout;
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while (!need_resched()) {
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HMT_low();
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HMT_very_low();
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if (likely(snooze_timeout_en) && get_tb() > snooze_exit_time) {
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/*
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* Task has not woken up but we are exiting the polling
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* loop anyway. Require a barrier after polling is
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* cleared to order subsequent test of need_resched().
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*/
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clear_thread_flag(TIF_POLLING_NRFLAG);
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smp_mb();
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break;
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}
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}
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HMT_medium();
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clear_thread_flag(TIF_POLLING_NRFLAG);
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local_irq_disable();
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idle_loop_epilog(in_purr);
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return index;
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}
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static void check_and_cede_processor(void)
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{
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/*
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* Ensure our interrupt state is properly tracked,
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* also checks if no interrupt has occurred while we
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* were soft-disabled
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*/
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if (prep_irq_for_idle()) {
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cede_processor();
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#ifdef CONFIG_TRACE_IRQFLAGS
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/* Ensure that H_CEDE returns with IRQs on */
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if (WARN_ON(!(mfmsr() & MSR_EE)))
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__hard_irq_enable();
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#endif
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}
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}
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static int dedicated_cede_loop(struct cpuidle_device *dev,
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struct cpuidle_driver *drv,
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int index)
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{
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unsigned long in_purr;
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idle_loop_prolog(&in_purr);
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get_lppaca()->donate_dedicated_cpu = 1;
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HMT_medium();
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check_and_cede_processor();
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local_irq_disable();
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get_lppaca()->donate_dedicated_cpu = 0;
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idle_loop_epilog(in_purr);
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return index;
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}
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static int shared_cede_loop(struct cpuidle_device *dev,
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struct cpuidle_driver *drv,
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int index)
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{
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unsigned long in_purr;
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idle_loop_prolog(&in_purr);
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/*
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* Yield the processor to the hypervisor. We return if
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* an external interrupt occurs (which are driven prior
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* to returning here) or if a prod occurs from another
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* processor. When returning here, external interrupts
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* are enabled.
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*/
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check_and_cede_processor();
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local_irq_disable();
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idle_loop_epilog(in_purr);
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return index;
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}
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/*
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* States for dedicated partition case.
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*/
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static struct cpuidle_state dedicated_states[] = {
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{ /* Snooze */
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.name = "snooze",
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.desc = "snooze",
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.exit_latency = 0,
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.target_residency = 0,
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.enter = &snooze_loop },
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{ /* CEDE */
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.name = "CEDE",
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.desc = "CEDE",
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.exit_latency = 10,
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.target_residency = 100,
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.enter = &dedicated_cede_loop },
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};
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/*
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* States for shared partition case.
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*/
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static struct cpuidle_state shared_states[] = {
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{ /* Snooze */
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.name = "snooze",
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.desc = "snooze",
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.exit_latency = 0,
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.target_residency = 0,
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.enter = &snooze_loop },
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{ /* Shared Cede */
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.name = "Shared Cede",
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.desc = "Shared Cede",
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.exit_latency = 10,
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.target_residency = 100,
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.enter = &shared_cede_loop },
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};
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static int pseries_cpuidle_cpu_online(unsigned int cpu)
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{
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struct cpuidle_device *dev = per_cpu(cpuidle_devices, cpu);
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if (dev && cpuidle_get_driver()) {
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cpuidle_pause_and_lock();
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cpuidle_enable_device(dev);
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cpuidle_resume_and_unlock();
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}
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return 0;
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}
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static int pseries_cpuidle_cpu_dead(unsigned int cpu)
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{
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struct cpuidle_device *dev = per_cpu(cpuidle_devices, cpu);
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if (dev && cpuidle_get_driver()) {
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cpuidle_pause_and_lock();
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cpuidle_disable_device(dev);
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cpuidle_resume_and_unlock();
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}
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return 0;
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}
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/*
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* pseries_cpuidle_driver_init()
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*/
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static int pseries_cpuidle_driver_init(void)
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{
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int idle_state;
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struct cpuidle_driver *drv = &pseries_idle_driver;
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drv->state_count = 0;
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for (idle_state = 0; idle_state < max_idle_state; ++idle_state) {
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/* Is the state not enabled? */
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if (cpuidle_state_table[idle_state].enter == NULL)
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continue;
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drv->states[drv->state_count] = /* structure copy */
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cpuidle_state_table[idle_state];
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drv->state_count += 1;
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}
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return 0;
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}
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/*
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* pseries_idle_probe()
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* Choose state table for shared versus dedicated partition
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*/
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static int pseries_idle_probe(void)
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{
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if (cpuidle_disable != IDLE_NO_OVERRIDE)
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return -ENODEV;
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if (firmware_has_feature(FW_FEATURE_SPLPAR)) {
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/*
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* Use local_paca instead of get_lppaca() since
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* preemption is not disabled, and it is not required in
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* fact, since lppaca_ptr does not need to be the value
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* associated to the current CPU, it can be from any CPU.
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*/
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if (lppaca_shared_proc(local_paca->lppaca_ptr)) {
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cpuidle_state_table = shared_states;
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max_idle_state = ARRAY_SIZE(shared_states);
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} else {
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cpuidle_state_table = dedicated_states;
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max_idle_state = ARRAY_SIZE(dedicated_states);
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}
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} else
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return -ENODEV;
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if (max_idle_state > 1) {
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snooze_timeout_en = true;
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snooze_timeout = cpuidle_state_table[1].target_residency *
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tb_ticks_per_usec;
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}
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return 0;
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}
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static int __init pseries_processor_idle_init(void)
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{
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int retval;
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retval = pseries_idle_probe();
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if (retval)
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return retval;
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pseries_cpuidle_driver_init();
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retval = cpuidle_register(&pseries_idle_driver, NULL);
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if (retval) {
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printk(KERN_DEBUG "Registration of pseries driver failed.\n");
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return retval;
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}
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retval = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
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"cpuidle/pseries:online",
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pseries_cpuidle_cpu_online, NULL);
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WARN_ON(retval < 0);
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retval = cpuhp_setup_state_nocalls(CPUHP_CPUIDLE_DEAD,
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"cpuidle/pseries:DEAD", NULL,
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pseries_cpuidle_cpu_dead);
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WARN_ON(retval < 0);
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printk(KERN_DEBUG "pseries_idle_driver registered\n");
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return 0;
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}
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device_initcall(pseries_processor_idle_init);
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