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Date:   Mon, 30 Mar 2020 10:43:26 -0700
From:   Kees Cook <keescook@chromium.org>
To:     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>
Subject: Re: [PATCH 3/3] kernel/hung_task convert hung_task_panic boot
 parameter to sysctl
Message-ID: <202003301042.97F3B00@keescook>
References: <20200330115535.3215-1-vbabka@suse.cz>
 <20200330115535.3215-4-vbabka@suse.cz>
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On Mon, Mar 30, 2020 at 01:55:35PM +0200, Vlastimil Babka wrote:
> We can now handle sysctl parameters on kernel command line and have
> infrastructure to convert legacy command line options that duplicate sysctl
> to become a sysctl alias.
> 
> This patch converts the hung_task_panic parameter. Note that the sysctl handler
> is more strict and allows only 0 and 1, while the legacy parameter allowed
> any non-zero value. But there is little reason anyone would not be using 1.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

I'll let others double-check, but I think this change should be okay. If
not, we can adjust the sysctl handler to accept an arbitrary int.

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  Documentation/admin-guide/kernel-parameters.txt |  2 +-
>  fs/proc/proc_sysctl.c                           |  1 +
>  kernel/hung_task.c                              | 10 ----------
>  3 files changed, 2 insertions(+), 11 deletions(-)
> 
> 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" },
> +	{"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
> 

-- 
Kees Cook