Re: [PATCH] sysctl: Add a group of macro functions to initcall the sysctl table of each feature

[Xiaoming Ni]

On 2021/12/7 9:38, Andrew Morton wrote:
> On Tue, 7 Dec 2021 09:13:20 +0800 Xiaoming Ni <nixiaoming@xxxxxxxxxx> wrote:
>
> > To avoid duplicated code, add a set of macro functions to initialize the
> > sysctl table for each feature.
> >
> > The system initialization process is as follows:
> >
> > 	start_kernel () {
> > 		...
> > 		/* init proc and sysctl base,
> > 		 * proc_root_init()-->proc_sys_init()-->sysctl_init_bases()
> > 		 */
> > 		proc_root_init(); /* init proc and sysctl base */
> > 		...
> > 		arch_call_rest_init();
> > 	}
> >
> > 	arch_call_rest_init()-->rest_init()-->kernel_init()
> > 	kernel_init() {
> > 		...
> > 		kernel_init_freeable(); /* do all initcalls */
> > 		...
> > 		do_sysctl_args(); /* Process the sysctl parameter: sysctl.*= */
> > 	}
> >
> > 	kernel_init_freeable()--->do_basic_setup()-->do_initcalls()
> > 	do_initcalls() {
> > 		for (level = 0; level < ARRAY_SIZE(initcall_levels) - 1; level++) {
> > 			do_initcall_level
> > 	}
> >
> > The sysctl interface of each subfeature should be registered after
> > sysctl_init_bases() and before do_sysctl_args(). It seems that the sysctl
> > interface does not depend on initcall_levels. To prevent the sysctl
> > interface from being initialized before the feature itself. The
> > lowest-level late_initcall() is used as the common sysctl interface
> > registration level.
>
> I'm not normally a fan of wrapping commonly-used code sequences into
> magical macros, but this one does seem to make sense.
>
> I wonder if it is possible to cook up a checkpatch rule to tell people
> to henceforth use the magic macros rather than to open-code things in
> the old way.  Sounds hard.
>
> > --- a/fs/coredump.c
> > +++ b/fs/coredump.c
> > @@ -943,12 +943,7 @@ static struct ctl_table coredump_sysctls[] = {
> >   	{ }
> >   };
> >   
> > -static int __init init_fs_coredump_sysctls(void)
> > -{
> > -	register_sysctl_init("kernel", coredump_sysctls);
> > -	return 0;
> > -}
> > -fs_initcall(init_fs_coredump_sysctls);
> > +kernel_sysctl_initcall(coredump_sysctls);
>
> But this and several like it are functional changes.
>
> >   #endif /* CONFIG_SYSCTL */
> >
> > ...
> >
> > --- a/fs/inode.c
> > +++ b/fs/inode.c
> > @@ -132,12 +132,7 @@ static struct ctl_table inodes_sysctls[] = {
> >   	{ }
> >   };
> >   
> > -static int __init init_fs_inode_sysctls(void)
> > -{
> > -	register_sysctl_init("fs", inodes_sysctls);
> > -	return 0;
> > -}
> > -early_initcall(init_fs_inode_sysctls);
> > +fs_sysctl_initcall(inodes_sysctls);
> >   #endif
>
> Here's another, of many.
>
> Someone made the decision to use early_initcall() here (why?) and this
> patch switches it to late_initcall()!  Worrisome.  Each such stealth
> conversion should be explained and justified, shouldn't it?

static noinline void __init kernel_init_freeable(void)
{
	...
	do_pre_smp_initcalls(); /* do early_initcall */
	lockup_detector_init();

	smp_init();
	sched_init_smp();

	padata_init();
	page_alloc_init_late();
	/* Initialize page ext after all struct pages are initialized. */
	page_ext_init();

	do_basic_setup();  /* do other initcall */
	...
}

Between do_pre_smp_initcalls() and do_basic_setup(), no sysctl interface 
window is configured. In addition, all sysctl data has initial values. 
Delayed configuration does not affect the behavior after startup.
So I think we can change it to late_initcall().


Thanks
Xiaoming Ni