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Subject: Re: [PATCH 3/3] kernel/hung_task convert hung_task_panic boot
 parameter to sysctl
To:     Kees Cook <keescook@chromium.org>, Vlastimil Babka <vbabka@suse.cz>
CC:     Luis Chamberlain <mcgrof@kernel.org>,
        Iurii Zaikin <yzaikin@google.com>,
        <linux-kernel@vger.kernel.org>, <linux-api@vger.kernel.org>,
        <linux-mm@kvack.org>,
        Ivan Teterevkov <ivan.teterevkov@nutanix.com>,
        Michal Hocko <mhocko@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        "Guilherme G . Piccoli" <gpiccoli@canonical.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Christian Brauner <christian.brauner@ubuntu.com>
References: <20200330115535.3215-1-vbabka@suse.cz>
 <20200330115535.3215-4-vbabka@suse.cz> <202003301042.97F3B00@keescook>
From:   John Hubbard <jhubbard@nvidia.com>
Message-ID: <13ae67d8-4b31-db20-7ba4-1602906a291e@nvidia.com>
Date:   Mon, 30 Mar 2020 17:34:15 -0700
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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
>>
>