[PATCH 5.10 118/593] sched/core: Initialize the idle task with preemption disabled
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: 2021-07-12 06:43:10
Also in:
lkml
Subsystem:
alpha port, arm port, arm64 port (aarch64 architecture), c-sky architecture, cpu hotplug, exec & binfmt api, elf, generic include/asm header files, linux for powerpc (32-bit and 64-bit), memory management - core, mips, openrisc architecture, parisc architecture, risc-v architecture, s390 architecture, scheduler, sparc + ultrasparc (sparc/sparc64), superh, synopsys arc architecture, tensilica xtensa port (xtensa), the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Richard Henderson, Matt Turner, Magnus Lindholm, Russell King, Catalin Marinas, Will Deacon, Guo Ren, Thomas Gleixner, Peter Zijlstra, Kees Cook, Arnd Bergmann, Madhavan Srinivasan, Andrew Morton, David Hildenbrand, Thomas Bogendoerfer, Jonas Bonn, Stefan Kristiansson, Stafford Horne, "James E.J. Bottomley", Helge Deller, Paul Walmsley, Palmer Dabbelt, Albert Ou, Heiko Carstens, Vasily Gorbik, Alexander Gordeev, Ingo Molnar, Juri Lelli, Vincent Guittot, "David S. Miller", Andreas Larsson, Yoshinori Sato, Rich Felker, John Paul Adrian Glaubitz, Vineet Gupta, Chris Zankel, Max Filippov, Linus Torvalds, Borislav Petkov, Dave Hansen
From: Valentin Schneider <redacted>
[ 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 <redacted>
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.com (local)
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 48099c6e1e4a..8aa7fa949c23 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 18e9727d3f64..feee5a3cd128 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 041d0de6a1b6..1a8d7eaf1ff7 100644
--- a/arch/csky/kernel/smp.c
+++ b/arch/csky/kernel/smp.c@@ -282,7 +282,6 @@ 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 093040f7e626..0cad990385c0 100644
--- a/arch/ia64/kernel/smpboot.c
+++ b/arch/ia64/kernel/smpboot.c@@ -440,7 +440,6 @@ 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 48d84d5fcc36..ff25926c5458 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 29c82ef2e207..e4dad76066ae 100644
--- a/arch/openrisc/kernel/smp.c
+++ b/arch/openrisc/kernel/smp.c@@ -134,8 +134,6 @@ 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 db7ac77bea3a..0760230be56f 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c@@ -1426,7 +1426,6 @@ 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 96167d55ed98..0b04e0eae3ab 100644
--- a/arch/riscv/kernel/smpboot.c
+++ b/arch/riscv/kernel/smpboot.c@@ -166,7 +166,6 @@ 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 6ede29907fbf..e38480eb58fa 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 791bc373418b..7db5460553b7 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c@@ -863,7 +863,6 @@ static void smp_init_secondary(void) set_cpu_flag(CIF_ASCE_SECONDARY); cpu_init(); rcu_cpu_starting(cpu); - preempt_disable(); init_cpu_timer(); vtime_init(); pfault_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 69485ca13665..a334dd0d7c42 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h@@ -43,7 +43,7 @@ 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 582387fc939f..8baff500914e 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c@@ -230,7 +230,6 @@ static void notrace start_secondary(void *unused) cpu_init_exception_handling(); cpu_init(); 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 b4449544390c..dd26a42e80a8 100644
--- a/init/main.c
+++ b/init/main.c@@ -914,11 +914,7 @@ 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 281addb694df..096945ef49ad 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c@@ -2392,7 +2392,7 @@ 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 57b236251884..bd3fa14fda1f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c@@ -6512,7 +6512,7 @@ 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; }
--
2.30.2