From f1a0a376ca0c4ef1fc3d24e3e502acbb5b795674 Mon Sep 17 00:00:00 2001 From: Valentin Schneider Date: Wed, 12 May 2021 10:46:36 +0100 Subject: sched/core: 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 Signed-off-by: Ingo Molnar Acked-by: Peter Zijlstra Link: https://lore.kernel.org/r/20210512094636.2958515-1-valentin.schneider@arm.com --- arch/openrisc/kernel/smp.c | 2 -- 1 file changed, 2 deletions(-) (limited to 'arch/openrisc') 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 */ -- cgit v1.2.3 From 7c3edd6d9cb4d8ea8db5b167dc2eee94d7e4667b Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 11 Jun 2021 10:28:16 +0200 Subject: sched,arch: Remove unused TASK_STATE offsets All 6 architectures define TASK_STATE in asm-offsets, but then never actually use it. Remove the definitions to make sure they never will. Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20210611082838.472811363@infradead.org --- arch/csky/kernel/asm-offsets.c | 1 - arch/h8300/kernel/asm-offsets.c | 1 - arch/microblaze/kernel/asm-offsets.c | 1 - arch/mips/kernel/asm-offsets.c | 1 - arch/openrisc/kernel/asm-offsets.c | 1 - arch/parisc/kernel/asm-offsets.c | 1 - 6 files changed, 6 deletions(-) (limited to 'arch/openrisc') diff --git a/arch/csky/kernel/asm-offsets.c b/arch/csky/kernel/asm-offsets.c index 17479860d43d..1cbcba4b0dd1 100644 --- a/arch/csky/kernel/asm-offsets.c +++ b/arch/csky/kernel/asm-offsets.c @@ -9,7 +9,6 @@ int main(void) { /* offsets into the task struct */ - DEFINE(TASK_STATE, offsetof(struct task_struct, state)); DEFINE(TASK_THREAD_INFO, offsetof(struct task_struct, stack)); DEFINE(TASK_FLAGS, offsetof(struct task_struct, flags)); DEFINE(TASK_PTRACE, offsetof(struct task_struct, ptrace)); diff --git a/arch/h8300/kernel/asm-offsets.c b/arch/h8300/kernel/asm-offsets.c index d4b53af657c8..65571ee15132 100644 --- a/arch/h8300/kernel/asm-offsets.c +++ b/arch/h8300/kernel/asm-offsets.c @@ -21,7 +21,6 @@ int main(void) { /* offsets into the task struct */ - OFFSET(TASK_STATE, task_struct, state); OFFSET(TASK_FLAGS, task_struct, flags); OFFSET(TASK_PTRACE, task_struct, ptrace); OFFSET(TASK_BLOCKED, task_struct, blocked); diff --git a/arch/microblaze/kernel/asm-offsets.c b/arch/microblaze/kernel/asm-offsets.c index 6c69ce7be2e8..b77dd188dec4 100644 --- a/arch/microblaze/kernel/asm-offsets.c +++ b/arch/microblaze/kernel/asm-offsets.c @@ -70,7 +70,6 @@ int main(int argc, char *argv[]) /* struct task_struct */ DEFINE(TS_THREAD_INFO, offsetof(struct task_struct, stack)); - DEFINE(TASK_STATE, offsetof(struct task_struct, state)); DEFINE(TASK_FLAGS, offsetof(struct task_struct, flags)); DEFINE(TASK_PTRACE, offsetof(struct task_struct, ptrace)); DEFINE(TASK_BLOCKED, offsetof(struct task_struct, blocked)); diff --git a/arch/mips/kernel/asm-offsets.c b/arch/mips/kernel/asm-offsets.c index 5735b2cd6f2a..04ca75278f02 100644 --- a/arch/mips/kernel/asm-offsets.c +++ b/arch/mips/kernel/asm-offsets.c @@ -78,7 +78,6 @@ void output_ptreg_defines(void) void output_task_defines(void) { COMMENT("MIPS task_struct offsets."); - OFFSET(TASK_STATE, task_struct, state); OFFSET(TASK_THREAD_INFO, task_struct, stack); OFFSET(TASK_FLAGS, task_struct, flags); OFFSET(TASK_MM, task_struct, mm); diff --git a/arch/openrisc/kernel/asm-offsets.c b/arch/openrisc/kernel/asm-offsets.c index 18c703d1d761..710651d5aaae 100644 --- a/arch/openrisc/kernel/asm-offsets.c +++ b/arch/openrisc/kernel/asm-offsets.c @@ -37,7 +37,6 @@ int main(void) { /* offsets into the task_struct */ - DEFINE(TASK_STATE, offsetof(struct task_struct, state)); DEFINE(TASK_FLAGS, offsetof(struct task_struct, flags)); DEFINE(TASK_PTRACE, offsetof(struct task_struct, ptrace)); DEFINE(TASK_THREAD, offsetof(struct task_struct, thread)); diff --git a/arch/parisc/kernel/asm-offsets.c b/arch/parisc/kernel/asm-offsets.c index cd2cc1b1648c..33113ba24054 100644 --- a/arch/parisc/kernel/asm-offsets.c +++ b/arch/parisc/kernel/asm-offsets.c @@ -42,7 +42,6 @@ int main(void) { DEFINE(TASK_THREAD_INFO, offsetof(struct task_struct, stack)); - DEFINE(TASK_STATE, offsetof(struct task_struct, state)); DEFINE(TASK_FLAGS, offsetof(struct task_struct, flags)); DEFINE(TASK_SIGPENDING, offsetof(struct task_struct, pending)); DEFINE(TASK_PTRACE, offsetof(struct task_struct, ptrace)); -- cgit v1.2.3