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Message-ID: <aFoD7nW-oswoZCT_@U-2FWC9VHC-2323.local>
Date: Tue, 24 Jun 2025 09:48:30 +0800
From: Feng Tang <feng.tang@...ux.alibaba.com>
To: Petr Mladek <pmladek@...e.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Steven Rostedt <rostedt@...dmis.org>,
Lance Yang <lance.yang@...ux.dev>, Jonathan Corbet <corbet@....net>,
linux-kernel@...r.kernel.org, paulmck@...nel.org,
john.ogness@...utronix.de
Subject: Re: [PATCH V2 3/5] sys_info: add help to translate sys_info string
to bitmap
On Mon, Jun 23, 2025 at 04:04:56PM +0200, Petr Mladek wrote:
> On Mon 2025-06-16 09:08:38, Feng Tang wrote:
> > Bitmap definition is hard to remember and decode. Add sysctl interface
> > to translate human readable string like "tasks,mem,timer,lock,ftrace,..."
> > to bitmap.
> >
> > Suggested-by: Petr Mladek <pmladek@...e.com>
> > Signed-off-by: Feng Tang <feng.tang@...ux.alibaba.com>
> > ---
> > include/linux/sys_info.h | 7 +++
> > lib/sys_info.c | 97 ++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 104 insertions(+)
> >
> > diff --git a/include/linux/sys_info.h b/include/linux/sys_info.h
> > index 79bf4a942e5f..0b49863cd414 100644
> > --- a/include/linux/sys_info.h
> > +++ b/include/linux/sys_info.h
> > @@ -16,5 +16,12 @@
> > #define SYS_SHOW_BLOCKED_TASKS 0x00000080
> >
> > extern void sys_show_info(unsigned long info_mask);
> > +extern unsigned long sys_info_parse_param(char *str);
> >
> > +#ifdef CONFIG_SYSCTL
> > +struct ctl_table;
> > +extern int sysctl_sys_info_handler(const struct ctl_table *ro_table, int write,
> > + void *buffer, size_t *lenp,
> > + loff_t *ppos);
> > +#endif
> > #endif /* _LINUX_SYS_INFO_H */
> > diff --git a/lib/sys_info.c b/lib/sys_info.c
> > index 90a79b5164c9..9693542435ba 100644
> > --- a/lib/sys_info.c
> > +++ b/lib/sys_info.c
> > @@ -5,6 +5,103 @@
> > #include <linux/console.h>
> > #include <linux/nmi.h>
> >
> > +struct sys_info_name {
> > + unsigned long bit;
> > + const char *name;
> > +};
> > +
> > +static const char sys_info_avail[] = "tasks,mem,timer,lock,ftrace,all_bt,blocked_tasks";
> > +
> > +static const struct sys_info_name si_names[] = {
> > + { SYS_SHOW_TASK_INFO, "tasks" },
> > + { SYS_SHOW_MEM_INFO, "mem" },
> > + { SYS_SHOW_TIMER_INFO, "timer" },
>
> I see that the naming is a bit inconsistent in using singulars
> vs. plurals. I suggest to use plulars when it makes sense.
> It means here:
>
> { SYS_SHOW_TIMERS_INFO, "timers" },
>
> > + { SYS_SHOW_LOCK_INFO, "lock" },
>
> and here
>
> { SYS_SHOW_LOCKS_INFO, "locks" },
Will change.
> > + { SYS_SHOW_FTRACE_INFO, "ftrace" },
> > + { SYS_SHOW_ALL_CPU_BT, "all_bt" },
> > + { SYS_SHOW_BLOCKED_TASKS, "blocked_tasks" },
> > +};
>
> [...]
>
> > +#ifdef CONFIG_SYSCTL
> > +int sysctl_sys_info_handler(const struct ctl_table *ro_table, int write,
> > + void *buffer, size_t *lenp,
> > + loff_t *ppos)
> > +{
> > + char names[sizeof(sys_info_avail) + 1];
> > + struct ctl_table table;
> > + unsigned long *si_bits_global;
> > + int i, ret, len;
> > +
> > + si_bits_global = ro_table->data;
> > +
> > + if (write) {
> > + unsigned long si_bits;
> > +
> > + table = *ro_table;
> > + table.data = names;
> > + table.maxlen = sizeof(names);
> > + ret = proc_dostring(&table, write, buffer, lenp, ppos);
> > + if (ret)
> > + return ret;
> > +
> > + si_bits = sys_info_parse_param(names);
> > + /*
> > + * The access to the global value is not synchronized.
> > + */
>
> Nit, the comment fits on a single line. I would use:
>
> /* The access to the global value is not synchronized. */
Yes.
> > + WRITE_ONCE(*si_bits_global, si_bits);
> > + return 0;
> > + } else {
> > + /* for 'read' operation */
> > + bool first = true;
> > + char *buf;
> > +
> > + buf = names;
> > + for (i = 0; i < ARRAY_SIZE(si_names); i++) {
> > + if (*si_bits_global & si_names[i].bit) {
> > +
> > + if (first) {
> > + first = false;
> > + } else {
> > + *buf = ',';
> > + buf++;
> > + }
> > +
> > + len = strlen(si_names[i].name);
> > + strncpy(buf, si_names[i].name, len);
>
> I am afraid of a buffer overflow when people add new entry into
> si_names[] table but they forget to update sys_info_avail[] string.
> I would prefer to limit the write to the buffer by the size of the buffer.
Indeed. In my v3 branch, I have also added a line to warn about it:
/*
* When 'si_names' gets updated, please make sure the 'sys_info_avail'
* below is updated accordingly.
*/
static const struct sys_info_name si_names[] = {
But still, better to do some handling in code as you suggested.
> Something like (on top of this patch):
>
> --- a/lib/sys_info.c
> +++ b/lib/sys_info.c
> @@ -50,7 +50,7 @@ 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;
> - int i, ret, len;
> + int i, ret;
>
> si_bits_global = ro_table->data;
>
> @@ -72,27 +72,18 @@ int sysctl_sys_info_handler(const struct ctl_table *ro_table, int write,
> return 0;
> } else {
> /* for 'read' operation */
> - bool first = true;
> - char *buf;
> + char *delim = "";
> + int len = 0;
>
> - buf = names;
> + names[0] = '\0';
> for (i = 0; i < ARRAY_SIZE(si_names); i++) {
> if (*si_bits_global & si_names[i].bit) {
> -
> - if (first) {
> - first = false;
> - } else {
> - *buf = ',';
> - buf++;
> - }
> -
> - len = strlen(si_names[i].name);
> - strncpy(buf, si_names[i].name, len);
> - buf += len;
> + len += scnprintf(names + len, sizeof(names) - len,
> + "%s%s", delim, si_names[i].name);
> + delim = ",";
> }
>
> }
> - *buf = '\0';
>
> table = *ro_table;
> table.data = names;
Thanks!
- Feng
> Best Regards,
> Petr
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