From: Valentin Schneider valentin.schneider@arm.com
[ Upstream commit f1a0a376ca0c4ef1fc3d24e3e502acbb5b795674 ]
As pointed out by commit
de9b8f5dcbd9 ("sched: Fix crash trying to dequeue/enqueue the idle thread")
init_idle() can and will be invoked more than once on the same idle task. At boot time, it is invoked for the boot CPU thread by sched_init(). Then smp_init() creates the threads for all the secondary CPUs and invokes init_idle() on them.
As the hotplug machinery brings the secondaries to life, it will issue calls to idle_thread_get(), which itself invokes init_idle() yet again. In this case it's invoked twice more per secondary: at _cpu_up(), and at bringup_cpu().
Given smp_init() already initializes the idle tasks for all *possible* CPUs, no further initialization should be required. Now, removing init_idle() from idle_thread_get() exposes some interesting expectations with regards to the idle task's preempt_count: the secondary startup always issues a preempt_disable(), requiring some reset of the preempt count to 0 between hot-unplug and hotplug, which is currently served by idle_thread_get() -> idle_init().
Given the idle task is supposed to have preemption disabled once and never see it re-enabled, it seems that what we actually want is to initialize its preempt_count to PREEMPT_DISABLED and leave it there. Do that, and remove init_idle() from idle_thread_get().
Secondary startups were patched via coccinelle:
@begone@ @@
-preempt_disable(); ... cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
Signed-off-by: Valentin Schneider valentin.schneider@arm.com Signed-off-by: Ingo Molnar mingo@kernel.org Acked-by: Peter Zijlstra peterz@infradead.org Link: https://lore.kernel.org/r/20210512094636.2958515-1-valentin.schneider@arm.co... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/alpha/kernel/smp.c | 1 - arch/arc/kernel/smp.c | 1 - arch/arm/kernel/smp.c | 1 - arch/arm64/include/asm/preempt.h | 2 +- arch/arm64/kernel/smp.c | 1 - arch/csky/kernel/smp.c | 1 - arch/ia64/kernel/smpboot.c | 1 - arch/mips/kernel/smp.c | 1 - arch/openrisc/kernel/smp.c | 2 -- arch/parisc/kernel/smp.c | 1 - arch/powerpc/kernel/smp.c | 1 - arch/riscv/kernel/smpboot.c | 1 - arch/s390/include/asm/preempt.h | 4 ++-- arch/s390/kernel/smp.c | 1 - arch/sh/kernel/smp.c | 2 -- arch/sparc/kernel/smp_32.c | 1 - arch/sparc/kernel/smp_64.c | 3 --- arch/x86/include/asm/preempt.h | 2 +- arch/x86/kernel/smpboot.c | 1 - arch/xtensa/kernel/smp.c | 1 - include/asm-generic/preempt.h | 2 +- init/main.c | 6 +----- kernel/fork.c | 2 +- kernel/sched/core.c | 2 +- kernel/smpboot.c | 1 - 25 files changed, 8 insertions(+), 34 deletions(-)
diff --git a/arch/alpha/kernel/smp.c b/arch/alpha/kernel/smp.c index f4dd9f3f3001..4b2575f936d4 100644 --- a/arch/alpha/kernel/smp.c +++ b/arch/alpha/kernel/smp.c @@ -166,7 +166,6 @@ smp_callin(void) DBGS(("smp_callin: commencing CPU %d current %p active_mm %p\n", cpuid, current, current->active_mm));
- preempt_disable(); cpu_startup_entry(CPUHP_AP_ONLINE_IDLE); }
diff --git a/arch/arc/kernel/smp.c b/arch/arc/kernel/smp.c index 52906d314537..db0e104d6835 100644 --- a/arch/arc/kernel/smp.c +++ b/arch/arc/kernel/smp.c @@ -189,7 +189,6 @@ void start_kernel_secondary(void) pr_info("## CPU%u LIVE ##: Executing Code...\n", cpu);
local_irq_enable(); - preempt_disable(); cpu_startup_entry(CPUHP_AP_ONLINE_IDLE); }
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c index 74679240a9d8..c7bb168b0d97 100644 --- a/arch/arm/kernel/smp.c +++ b/arch/arm/kernel/smp.c @@ -432,7 +432,6 @@ asmlinkage void secondary_start_kernel(void) #endif pr_debug("CPU%u: Booted secondary processor\n", cpu);
- preempt_disable(); trace_hardirqs_off();
/* diff --git a/arch/arm64/include/asm/preempt.h b/arch/arm64/include/asm/preempt.h index 80e946b2abee..e83f0982b99c 100644 --- a/arch/arm64/include/asm/preempt.h +++ b/arch/arm64/include/asm/preempt.h @@ -23,7 +23,7 @@ static inline void preempt_count_set(u64 pc) } while (0)
#define init_idle_preempt_count(p, cpu) do { \ - task_thread_info(p)->preempt_count = PREEMPT_ENABLED; \ + task_thread_info(p)->preempt_count = PREEMPT_DISABLED; \ } while (0)
static inline void set_preempt_need_resched(void) diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index 357590beaabb..48fd89256739 100644 --- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c @@ -223,7 +223,6 @@ asmlinkage notrace void secondary_start_kernel(void) init_gic_priority_masking();
rcu_cpu_starting(cpu); - preempt_disable(); trace_hardirqs_off();
/* diff --git a/arch/csky/kernel/smp.c b/arch/csky/kernel/smp.c index 0f9f5eef9338..e2993539af8e 100644 --- a/arch/csky/kernel/smp.c +++ b/arch/csky/kernel/smp.c @@ -281,7 +281,6 @@ void csky_start_secondary(void) pr_info("CPU%u Online: %s...\n", cpu, __func__);
local_irq_enable(); - preempt_disable(); cpu_startup_entry(CPUHP_AP_ONLINE_IDLE); }
diff --git a/arch/ia64/kernel/smpboot.c b/arch/ia64/kernel/smpboot.c index 49b488580939..d10f780c13b9 100644 --- a/arch/ia64/kernel/smpboot.c +++ b/arch/ia64/kernel/smpboot.c @@ -441,7 +441,6 @@ start_secondary (void *unused) #endif efi_map_pal_code(); cpu_init(); - preempt_disable(); smp_callin();
cpu_startup_entry(CPUHP_AP_ONLINE_IDLE); diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c index ef86fbad8546..d542fb7af3ba 100644 --- a/arch/mips/kernel/smp.c +++ b/arch/mips/kernel/smp.c @@ -348,7 +348,6 @@ asmlinkage void start_secondary(void) */
calibrate_delay(); - preempt_disable(); cpu = smp_processor_id(); cpu_data[cpu].udelay_val = loops_per_jiffy;
diff --git a/arch/openrisc/kernel/smp.c b/arch/openrisc/kernel/smp.c index 48e1092a64de..415e209732a3 100644 --- a/arch/openrisc/kernel/smp.c +++ b/arch/openrisc/kernel/smp.c @@ -145,8 +145,6 @@ asmlinkage __init void secondary_start_kernel(void) set_cpu_online(cpu, true);
local_irq_enable(); - - preempt_disable(); /* * OK, it's off to the idle thread for us */ diff --git a/arch/parisc/kernel/smp.c b/arch/parisc/kernel/smp.c index 10227f667c8a..1405b603b91b 100644 --- a/arch/parisc/kernel/smp.c +++ b/arch/parisc/kernel/smp.c @@ -302,7 +302,6 @@ void __init smp_callin(unsigned long pdce_proc) #endif
smp_cpu_init(slave_id); - preempt_disable();
flush_cache_all_local(); /* start with known state */ flush_tlb_all_local(NULL); diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c index c2473e20f5f5..1d7daef1c3b6 100644 --- a/arch/powerpc/kernel/smp.c +++ b/arch/powerpc/kernel/smp.c @@ -1530,7 +1530,6 @@ void start_secondary(void *unused) smp_store_cpu_info(cpu); set_dec(tb_ticks_per_jiffy); rcu_cpu_starting(cpu); - preempt_disable(); cpu_callin_map[cpu] = 1;
if (smp_ops->setup_cpu) diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c index 5e276c25646f..1941a6ce86a1 100644 --- a/arch/riscv/kernel/smpboot.c +++ b/arch/riscv/kernel/smpboot.c @@ -176,7 +176,6 @@ asmlinkage __visible void smp_callin(void) * Disable preemption before enabling interrupts, so we don't try to * schedule a CPU that hasn't actually started yet. */ - preempt_disable(); local_irq_enable(); cpu_startup_entry(CPUHP_AP_ONLINE_IDLE); } diff --git a/arch/s390/include/asm/preempt.h b/arch/s390/include/asm/preempt.h index b49e0492842c..23ff51be7e29 100644 --- a/arch/s390/include/asm/preempt.h +++ b/arch/s390/include/asm/preempt.h @@ -32,7 +32,7 @@ static inline void preempt_count_set(int pc) #define init_task_preempt_count(p) do { } while (0)
#define init_idle_preempt_count(p, cpu) do { \ - S390_lowcore.preempt_count = PREEMPT_ENABLED; \ + S390_lowcore.preempt_count = PREEMPT_DISABLED; \ } while (0)
static inline void set_preempt_need_resched(void) @@ -91,7 +91,7 @@ static inline void preempt_count_set(int pc) #define init_task_preempt_count(p) do { } while (0)
#define init_idle_preempt_count(p, cpu) do { \ - S390_lowcore.preempt_count = PREEMPT_ENABLED; \ + S390_lowcore.preempt_count = PREEMPT_DISABLED; \ } while (0)
static inline void set_preempt_need_resched(void) diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c index 58c8afa3da65..d60c7374d807 100644 --- a/arch/s390/kernel/smp.c +++ b/arch/s390/kernel/smp.c @@ -877,7 +877,6 @@ static void smp_init_secondary(void) restore_access_regs(S390_lowcore.access_regs_save_area); cpu_init(); rcu_cpu_starting(cpu); - preempt_disable(); init_cpu_timer(); vtime_init(); vdso_getcpu_init(); diff --git a/arch/sh/kernel/smp.c b/arch/sh/kernel/smp.c index 372acdc9033e..65924d9ec245 100644 --- a/arch/sh/kernel/smp.c +++ b/arch/sh/kernel/smp.c @@ -186,8 +186,6 @@ asmlinkage void start_secondary(void)
per_cpu_trap_init();
- preempt_disable(); - notify_cpu_starting(cpu);
local_irq_enable(); diff --git a/arch/sparc/kernel/smp_32.c b/arch/sparc/kernel/smp_32.c index 50c127ab46d5..22b148e5a5f8 100644 --- a/arch/sparc/kernel/smp_32.c +++ b/arch/sparc/kernel/smp_32.c @@ -348,7 +348,6 @@ static void sparc_start_secondary(void *arg) */ arch_cpu_pre_starting(arg);
- preempt_disable(); cpu = smp_processor_id();
notify_cpu_starting(cpu); diff --git a/arch/sparc/kernel/smp_64.c b/arch/sparc/kernel/smp_64.c index e38d8bf454e8..ae5faa1d989d 100644 --- a/arch/sparc/kernel/smp_64.c +++ b/arch/sparc/kernel/smp_64.c @@ -138,9 +138,6 @@ void smp_callin(void)
set_cpu_online(cpuid, true);
- /* idle thread is expected to have preempt disabled */ - preempt_disable(); - local_irq_enable();
cpu_startup_entry(CPUHP_AP_ONLINE_IDLE); diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h index f8cb8af4de5c..fe5efbcba824 100644 --- a/arch/x86/include/asm/preempt.h +++ b/arch/x86/include/asm/preempt.h @@ -44,7 +44,7 @@ static __always_inline void preempt_count_set(int pc) #define init_task_preempt_count(p) do { } while (0)
#define init_idle_preempt_count(p, cpu) do { \ - per_cpu(__preempt_count, (cpu)) = PREEMPT_ENABLED; \ + per_cpu(__preempt_count, (cpu)) = PREEMPT_DISABLED; \ } while (0)
/* diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 363b36bbd791..ebc4b13b74a4 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -236,7 +236,6 @@ static void notrace start_secondary(void *unused) cpu_init(); rcu_cpu_starting(raw_smp_processor_id()); x86_cpuinit.early_percpu_clock_init(); - preempt_disable(); smp_callin();
enable_start_cpu0 = 0; diff --git a/arch/xtensa/kernel/smp.c b/arch/xtensa/kernel/smp.c index cd85a7a2722b..1254da07ead1 100644 --- a/arch/xtensa/kernel/smp.c +++ b/arch/xtensa/kernel/smp.c @@ -145,7 +145,6 @@ void secondary_start_kernel(void) cpumask_set_cpu(cpu, mm_cpumask(mm)); enter_lazy_tlb(mm, current);
- preempt_disable(); trace_hardirqs_off();
calibrate_delay(); diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h index d683f5e6d791..b4d43a4af5f7 100644 --- a/include/asm-generic/preempt.h +++ b/include/asm-generic/preempt.h @@ -29,7 +29,7 @@ static __always_inline void preempt_count_set(int pc) } while (0)
#define init_idle_preempt_count(p, cpu) do { \ - task_thread_info(p)->preempt_count = PREEMPT_ENABLED; \ + task_thread_info(p)->preempt_count = PREEMPT_DISABLED; \ } while (0)
static __always_inline void set_preempt_need_resched(void) diff --git a/init/main.c b/init/main.c index 5bd1a25f1d6f..c97d3c0247a1 100644 --- a/init/main.c +++ b/init/main.c @@ -918,11 +918,7 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void) * time - but meanwhile we still have a functioning scheduler. */ sched_init(); - /* - * Disable preemption - early bootup scheduling is extremely - * fragile until we cpu_idle() for the first time. - */ - preempt_disable(); + if (WARN(!irqs_disabled(), "Interrupts were enabled *very* early, fixing it\n")) local_irq_disable(); diff --git a/kernel/fork.c b/kernel/fork.c index 321a5e31d817..2654a5a9e5df 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2405,7 +2405,7 @@ static inline void init_idle_pids(struct task_struct *idle) } }
-struct task_struct *fork_idle(int cpu) +struct task_struct * __init fork_idle(int cpu) { struct task_struct *task; struct kernel_clone_args args = { diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 814200541f8f..e25b2d8ec18d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7428,7 +7428,7 @@ void show_state_filter(unsigned long state_filter) * NOTE: this function does not set the idle thread's NEED_RESCHED * flag, to make booting more robust. */ -void init_idle(struct task_struct *idle, int cpu) +void __init init_idle(struct task_struct *idle, int cpu) { struct rq *rq = cpu_rq(cpu); unsigned long flags; diff --git a/kernel/smpboot.c b/kernel/smpboot.c index f25208e8df83..e4163042c4d6 100644 --- a/kernel/smpboot.c +++ b/kernel/smpboot.c @@ -33,7 +33,6 @@ struct task_struct *idle_thread_get(unsigned int cpu)
if (!tsk) return ERR_PTR(-ENOMEM); - init_idle(tsk, cpu); return tsk; }