linux-kernel - Re: [PATCH] proc/proc_sysctl: Modify the order of scheduling function calls

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Date:   Mon, 5 Sep 2022 04:12:11 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Li zeming <zeming@...china.com>
Cc:     mcgrof@...nel.org, keescook@...omium.org, yzaikin@...gle.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] proc/proc_sysctl: Modify the order of scheduling
 function calls

On Mon, Sep 05, 2022 at 09:29:25AM +0800, Li zeming wrote:
> When the ctl_table_header object is judged to be valid, the scheduling
> check is performed again.

No, we want the check in all cases, even if the header is NULL.

> Signed-off-by: Li zeming <zeming@...china.com>
> ---
>  fs/proc/proc_sysctl.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index 50ba9e4fb284..36921e2ebeb0 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -1729,11 +1729,10 @@ static void drop_sysctl_table(struct ctl_table_header *header)
>  void unregister_sysctl_table(struct ctl_table_header * header)
>  {
>  	int nr_subheaders;
> -	might_sleep();
> -
>  	if (header == NULL)
>  		return;
>  
> +	might_sleep();
>  	nr_subheaders = count_subheaders(header->ctl_table_arg);
>  	if (unlikely(nr_subheaders > 1)) {
>  		struct ctl_table_header **subheaders;
> -- 
> 2.18.2
>