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

John Hubbard
2020-03-31T00:34:19Z

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
>>
>