linux-kernel - Re: [PATCH v1 4/7] panic: sys_info: Replace struct sys_info

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Message-ID: <aHEr8NO4xHGPNjJo@U-2FWC9VHC-2323.local>
Date: Fri, 11 Jul 2025 23:21:20 +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 4/7] panic: sys_info: Replace struct sys_info_name
 with plain array of strings

On Fri, Jul 11, 2025 at 12:51:10PM +0300, Andy Shevchenko wrote:
> There is no need to keep a custom structure just for the need of
> a plain array of strings. Replace struct sys_info_name with plain
> array of strings.
> 
> With that done, simplify the code, in particular, naturally use
> for_each_set_bit() when iterating over si_bits_global bitmap.

My earlier reply seems to get lost, so I'll resend. (Please ignore this
if your alreay received the reply to 4/7 patch.)

IIUC, this will not work.

Actually there is a hole in the bitmap definition:

#define SYS_INFO_PANIC_CONSOLE_REPLAY	0x00000020

Ad Petr pointed in his review, it's only for panic use, that's why
we make it invisible in sys_info.c. Eventually, we plan to deprecate
'panic_print', and use 'panic_sys_info' and 'panic_console_replay' to
replace it. After that happens that user only see string interface,
we can change these bitmap definition and remove the hole, and use
your cleanup here.

Thanks,
Feng

> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  lib/sys_info.c | 47 ++++++++++++++++++++---------------------------
>  1 file changed, 20 insertions(+), 27 deletions(-)
> 
> diff --git a/lib/sys_info.c b/lib/sys_info.c
> index 5d98560f3f53..7965984c6d67 100644
> --- a/lib/sys_info.c
> +++ b/lib/sys_info.c
> @@ -1,30 +1,28 @@
>  // SPDX-License-Identifier: GPL-2.0-only
> -#include <linux/sched/debug.h>
> +#include <linux/bitops.h>
>  #include <linux/console.h>
> +#include <linux/log2.h>
>  #include <linux/kernel.h>
>  #include <linux/ftrace.h>
> -#include <linux/sysctl.h>
>  #include <linux/nmi.h>
> +#include <linux/sched/debug.h>
> +#include <linux/string.h>
> +#include <linux/sysctl.h>
>  
>  #include <linux/sys_info.h>
>  
> -struct sys_info_name {
> -	unsigned long bit;
> -	const char *name;
> -};
> -
>  /*
>   * When 'si_names' gets updated,  please make sure the 'sys_info_avail'
>   * below is updated accordingly.
>   */
> -static const struct sys_info_name  si_names[] = {
> -	{ SYS_INFO_TASKS,		"tasks" },
> -	{ SYS_INFO_MEM,			"mem" },
> -	{ SYS_INFO_TIMERS,		"timers" },
> -	{ SYS_INFO_LOCKS,		"locks" },
> -	{ SYS_INFO_FTRACE,		"ftrace" },
> -	{ SYS_INFO_ALL_BT,		"all_bt" },
> -	{ SYS_INFO_BLOCKED_TASKS,	"blocked_tasks" },
> +static const char * const si_names[] = {
> +	[ilog2(SYS_INFO_TASKS)]		= "tasks",
> +	[ilog2(SYS_INFO_MEM)]		= "mem",
> +	[ilog2(SYS_INFO_TIMERS)]	= "timers",
> +	[ilog2(SYS_INFO_LOCKS)]		= "locks",
> +	[ilog2(SYS_INFO_FTRACE)]	= "ftrace",
> +	[ilog2(SYS_INFO_ALL_BT)]	= "all_bt",
> +	[ilog2(SYS_INFO_BLOCKED_TASKS)]	= "blocked_tasks",
>  };
>  
>  /* Expecting string like "xxx_sys_info=tasks,mem,timers,locks,ftrace,..." */
> @@ -36,12 +34,9 @@ unsigned long sys_info_parse_param(char *str)
>  
>  	s = str;
>  	while ((name = strsep(&s, ",")) && *name) {
> -		for (i = 0; i < ARRAY_SIZE(si_names); i++) {
> -			if (!strcmp(name, si_names[i].name)) {
> -				si_bits |= si_names[i].bit;
> -				break;
> -			}
> -		}
> +		i = match_string(si_names, ARRAY_SIZE(si_names), name);
> +		if (i >= 0)
> +			__set_bit(i, &si_bits);
>  	}
>  
>  	return si_bits;
> @@ -84,12 +79,10 @@ int sysctl_sys_info_handler(const struct ctl_table *ro_table, int write,
>  		/* The access to the global value is not synchronized. */
>  		si_bits = READ_ONCE(*si_bits_global);
>  
> -		for (i = 0; i < ARRAY_SIZE(si_names); i++) {
> -			if (si_bits & si_names[i].bit) {
> -				len += scnprintf(names + len, sizeof(names) - len,
> -					"%s%s", delim, si_names[i].name);
> -				delim = ",";
> -			}
> +		for_each_set_bit(i, &si_bits, ARRAY_SIZE(si_names)) {
> +			len += scnprintf(names + len, sizeof(names) - len,
> +					 "%s%s", delim, si_names[i]);
> +			delim = ",";
>  		}
>  
>  		table = *ro_table;
> -- 
> 2.47.2