Commit 36cb0e1c authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

fork: Explicity test for idle tasks in copy_thread 

The architectures ia64 and parisc have special handling for the idle
thread in copy_process.  Add a flag named idle to kernel_clone_args
and use it to explicity test if an idle process is being created.

Fullfill the expectations of the rest of the copy_thread
implemetations and pass a function pointer in .stack from fork_idle().
This makes what is happening in copy_thread better defined, and is
useful to make idle threads less special.

Link: https://lkml.kernel.org/r/20220506141512.516114-3-ebiederm@xmission.com


Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent c5febea0

arch/ia64/kernel/process.c

+1 −1
Original line number Diff line number Diff line
@@ -342,7 +342,7 @@ copy_thread(struct task_struct *p, const struct kernel_clone_args *args) 
	ia64_drop_fpu(p);	/* don't pick up stale state from a CPU's fph */



	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {

		if (unlikely(!user_stack_base)) {

		if (unlikely(args->idle)) {

			/* fork_idle() called us */

			return 0;

		}

arch/parisc/kernel/process.c

+1 −1
Original line number Diff line number Diff line
@@ -224,7 +224,7 @@ copy_thread(struct task_struct *p, const struct kernel_clone_args *args) 
	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {

		/* kernel thread */

		memset(cregs, 0, sizeof(struct pt_regs));

		if (!usp) /* idle thread */

		if (args->idle) /* idle thread */

			return 0;

		/* Must exit via ret_from_kernel_thread in order

		 * to call schedule_tail()

include/linux/sched/task.h

+1 −0
Original line number Diff line number Diff line
@@ -33,6 +33,7 @@ struct kernel_clone_args { 
	int cgroup;

	int io_thread;

	int kthread;

	int idle;

	struct cgroup *cgrp;

	struct css_set *cset;

};

kernel/fork.c

+9 −0
Original line number Diff line number Diff line
@@ -2544,12 +2544,21 @@ static inline void init_idle_pids(struct task_struct *idle) 
	}

}



static int idle_dummy(void *dummy)

{

	/* This function is never called */

	return 0;

}



struct task_struct * __init fork_idle(int cpu)

{

	struct task_struct *task;

	struct kernel_clone_args args = {

		.flags		= CLONE_VM,

		.stack		= (unsigned long)&idle_dummy,

		.stack_size	= (unsigned long)NULL,

		.kthread	= 1,

		.idle		= 1,

	};



	task = copy_process(&init_struct_pid, 0, cpu_to_node(cpu), &args);