Re: [PATCH 3/3] kernel/hung_task convert hung_task_panic boot parameter to sysctl

[John Hubbard]

On 3/30/20 10:43 AM, Kees Cook wrote:
...
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 81ff626fc700..e0b8840404a1 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -1457,7 +1457,7 @@
> >   			[KNL] Should the hung task detector generate panics.
> >   			Format: <integer>
> >   
> > -			A nonzero value instructs the kernel to panic when a
> > +			A value of 1 instructs the kernel to panic when a
> >   			hung task is detected. The default value is controlled
> >   			by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
> >   			option. The value selected by this boot parameter can
> > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> > index 97eb0b552bf8..77b1b844b02b 100644
> > --- a/fs/proc/proc_sysctl.c
> > +++ b/fs/proc/proc_sysctl.c
> > @@ -1743,6 +1743,7 @@ struct sysctl_alias {
> >    */
> >   static const struct sysctl_alias sysctl_aliases[] = {
> >   	{"numa_zonelist_order",		"vm.numa_zonelist_order" },


Hi Vlastimil,

Maybe best to delete the above line? Because:

    a) it was added as an example, and now that you have a real use case in this patch,
       the example is no longer required, and

    b) numa_zonelist_order is deprecated, as a boot param. Adding support to it in this
       brand-new mechanism seems to be going a bit in the opposite direction of deprecation.

And, I don't think you really want all the sysctls to be enabled as boot params, right? Your
comment right above sysctl_aliases[] (shown in patch 2) sort of indicates that only some items
are meant to be both sysctl's and boot params. And that makes sense.

In fact, the sysctl_aliases[] is (or could be) effectively the whitelist that Luis Chamberlain
was requesting in another thread. A whitelist makes good sense, for the reasons Luis listed.
As such, keeping it limited to items that we want, seems like the way to go, IMHO.


thanks,
--
John Hubbard
NVIDIA


> > +	{"hung_task_panic",		"kernel.hung_task_panic" },
> >   	{ }
> >   };
> >   
> > diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> > index 14a625c16cb3..b22b5eeab3cb 100644
> > --- a/kernel/hung_task.c
> > +++ b/kernel/hung_task.c
> > @@ -63,16 +63,6 @@ static struct task_struct *watchdog_task;
> >   unsigned int __read_mostly sysctl_hung_task_panic =
> >   				CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
> >   
> > -static int __init hung_task_panic_setup(char *str)
> > -{
> > -	int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
> > -
> > -	if (rc)
> > -		return rc;
> > -	return 1;
> > -}
> > -__setup("hung_task_panic=", hung_task_panic_setup);
> > -
> >   static int
> >   hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
> >   {
> > --
> > 2.25.1