linux-kernel - Re: [PATCH v1 3/7] panic: sys_info: Capture si_bits

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Message-ID: <aHEmIdgXvOeHtgMM@U-2FWC9VHC-2323.local>
Date: Fri, 11 Jul 2025 22:56:33 +0800
From: Feng Tang <feng.tang@...ux.alibaba.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Petr Mladek <pmladek@...e.com>
Cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
	Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH v1 3/7] panic: sys_info: Capture si_bits_global before
 iterating over it

Hi Andy,

Thanks for the patch! please cc Petr Mladek <pmladek@...e.com> for changes
as I mentioned in the cover letter, he contributed a lot to the code and arch
from RFC to v3.

On Fri, Jul 11, 2025 at 12:51:09PM +0300, Andy Shevchenko wrote:
> The for-loop might re-read the content of the memory the si_bits_global
> points to on each iteration. Instead, just capture it for the sake of
> consistency and use that instead.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  lib/sys_info.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/sys_info.c b/lib/sys_info.c
> index 44bc6d96b702..5d98560f3f53 100644
> --- a/lib/sys_info.c
> +++ b/lib/sys_info.c
> @@ -58,11 +58,11 @@ int sysctl_sys_info_handler(const struct ctl_table *ro_table, int write,
>  	char names[sizeof(sys_info_avail) + 1];
>  	struct ctl_table table;
>  	unsigned long *si_bits_global;
> +	unsigned long si_bits;
>  
>  	si_bits_global = ro_table->data;
>  
>  	if (write) {
> -		unsigned long si_bits;
>  		int ret;
>  
>  		table = *ro_table;
> @@ -81,8 +81,11 @@ int sysctl_sys_info_handler(const struct ctl_table *ro_table, int write,
>  		char *delim = "";
>  		int i, len = 0;
>  
> +		/* The access to the global value is not synchronized. */
> +		si_bits = READ_ONCE(*si_bits_global);

Good catch!

Thanks,
Feng

> +
>  		for (i = 0; i < ARRAY_SIZE(si_names); i++) {
> -			if (*si_bits_global & si_names[i].bit) {
> +			if (si_bits & si_names[i].bit) {
>  				len += scnprintf(names + len, sizeof(names) - len,
>  					"%s%s", delim, si_names[i].name);
>  				delim = ",";
> -- 
> 2.47.2
>