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Message-Id: <20210512094636.2958515-1-valentin.schneider@arm.com>
Date: Wed, 12 May 2021 10:46:36 +0100
From: Valentin Schneider <valentin.schneider@....com>
To: linux-kernel@...r.kernel.org, linux-alpha@...r.kernel.org,
linux-snps-arc@...ts.infradead.org,
linux-arm-kernel@...ts.infradead.org, linux-csky@...r.kernel.org,
linux-ia64@...r.kernel.org, linux-mips@...r.kernel.org,
openrisc@...ts.librecores.org, linux-parisc@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
sparclinux@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
linux-arch@...r.kernel.org
Cc: mingo@...nel.org, peterz@...radead.org, tglx@...utronix.de,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>, bristot@...hat.com,
yejune.deng@...il.com
Subject: [PATCH] sched: Initialize the idle task with preemption disabled
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@....com>
---
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 5a4d59a1070d..055ca3816eb7 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1505,7 +1505,6 @@ 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 16703c35a944..29713d0cf155 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 53b278845b88..d8580323110e 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 a1a763019bfb..9de7bc40be1d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2406,7 +2406,7 @@ 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 4a0668acd876..43b903ae823b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7433,7 +7433,7 @@ 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;
}
--
2.25.1
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