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fork: Explicity test for idle tasks in copy_thread

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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: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman
2022-04-11 16:17:28 -05:00
parent c5febea095
commit 36cb0e1cda
4 changed files with 12 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
arch/ia64/kernel/process.c
View File

@@ -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;
}

2
arch/parisc/kernel/process.c
View File

@@ -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()

1
include/linux/sched/task.h
View File

@@ -33,6 +33,7 @@ struct kernel_clone_args {
int cgroup;
int io_thread;
int kthread;
int idle;
struct cgroup *cgrp;
struct css_set *cset;
};

9
kernel/fork.c
View File

@@ -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);