On (04/08/16 12:04), Pan Xinhui wrote:
[..]
> > +/*
> > + * Init async printk via late_initcall, after core/arch/device/etc.
> > + * initialization.
> > + */
> > +static __init int init_printk_kthread(void)
> > +{
> > + printk_initcall_done = true;
> > + return __init_printk_kthread();
> hello,
>
> One confusion, Why not use a lock to protect __init_printk_kthread from
> parallel call? Otherwise I think there is a race.
> But for simplicity, maybe you could write codes as below.
>
> + int ret = __init_printk_kthread();
> + printk_initcall_done = true;
> + return ret;
>
> In my opinion, using a lock is better.
Hello,
I though about this, but isn't late_initcall() happening before kernel
starts /sbin/init? who can race with
late_initcall() -> init_printk_kthread() -> __init_printk_kthread()?
looking at
static int __ref kernel_init(void *unused)
{
int ret;
kernel_init_freeable();
/* need to finish all async __init code before freeing the memory */
async_synchronize_full();
free_initmem();
..
if (!try_to_run_init_process("/sbin/init") ||
!try_to_run_init_process("/etc/init") ||
!try_to_run_init_process("/bin/init") ||
!try_to_run_init_process("/bin/sh"))
return 0;
__init (and init_printk_kthread is __init) is finished and freed by the
time kernel try_to_run_init_process. isn't it?
sysfs knob -> __init_printk_kthread() is protected by printk_sync_lock
mutex, obviously there can be parallel calls from user space.
-ss
