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: "Eric W. Biederman" <ebiederm@xmission.com>

diff --git a/arch/ia64/kernel/process.c b/arch/ia64/kernel/process.c
index 10d41ded05a5cb684e33d013d3e5bef7fada6af9..8f010ae818bc2a0d65ef5da806f37ee3eab3db47 100644 (file)
--- a/arch/ia64/kernel/process.c
+++ b/arch/ia64/kernel/process.c
@@ -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;
                }

diff --git a/arch/parisc/kernel/process.c b/arch/parisc/kernel/process.c
index 129c17de45ba5b8dc7716c4ad6e841b539c62651..30a5874ca8458484e7e03ccaf5bce1c8337d2222 100644 (file)
--- a/arch/parisc/kernel/process.c
+++ b/arch/parisc/kernel/process.c
@@ -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()

diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index fcdcba231aac98022c2393ab1f24007d7ed4106f..3d6b99ce540843ff1c4246d752d50265aa5458b1 100644 (file)
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -33,6 +33,7 @@ struct kernel_clone_args {
        int cgroup;
        int io_thread;
        int kthread;
+       int idle;
        struct cgroup *cgrp;
        struct css_set *cset;
 };

diff --git a/kernel/fork.c b/kernel/fork.c
index d39a248a8d8db1d25080bed11446659eca40d974..93d77ee921ff5db871cbb13e4ff4387db27229c0 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -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);