[PATCH v3 4/6] panic: sys_info: Rewrite a fix for a compilation error (`make W=1`)

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

Compiler was not happy about dead variable in use:

lib/sys_info.c:52:19: error: variable 'sys_info_avail' is not needed and will not be emitted [-Werror,-Wunneeded-internal-declaration]
   52 | static const char sys_info_avail[] = "tasks,mem,timers,locks,ftrace,all_bt,blocked_tasks";
      |                   ^~~~~~~~~~~~~~

This was fixed by adding __maybe_unused attribute that just hides the issue
and didn't actually fix the root cause. Rewrite the fix by moving the local
variable from stack to a heap.

As a side effect this drops unneeded "synchronisation" of duplicative info
and also makes code ready for the further refactoring.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 lib/sys_info.c | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/lib/sys_info.c b/lib/sys_info.c
index 29a63238b31d..eb5c1226bfc8 100644
--- a/lib/sys_info.c
+++ b/lib/sys_info.c
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-only
+#include <linux/array_size.h>
 #include <linux/bitops.h>
+#include <linux/cleanup.h>
 #include <linux/console.h>
 #include <linux/log2.h>
 #include <linux/kernel.h>
@@ -11,10 +13,6 @@
 
 #include <linux/sys_info.h>
 
-/*
- * When 'si_names' gets updated,  please make sure the 'sys_info_avail'
- * below is updated accordingly.
- */
 static const char * const si_names[] = {
 	[ilog2(SYS_INFO_TASKS)]			= "tasks",
 	[ilog2(SYS_INFO_MEM)]			= "mem",
@@ -45,25 +43,32 @@ unsigned long sys_info_parse_param(char *str)
 
 #ifdef CONFIG_SYSCTL
 
-static const char sys_info_avail[] __maybe_unused = "tasks,mem,timers,locks,ftrace,all_bt,blocked_tasks";
-
 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)];
 	struct ctl_table table;
 	unsigned long *si_bits_global;
 	unsigned long si_bits;
+	unsigned int i;
+	size_t maxlen;
 
 	si_bits_global = ro_table->data;
 
+	maxlen = 0;
+	for (i = 0; i < ARRAY_SIZE(si_names); i++)
+		maxlen += strlen(si_names[i]) + 1;
+
+	char *names __free(kfree) = kzalloc(maxlen, GFP_KERNEL);
+	if (!names)
+		return -ENOMEM;
+
 	if (write) {
 		int ret;
 
 		table = *ro_table;
 		table.data = names;
-		table.maxlen = sizeof(names);
+		table.maxlen = maxlen;
 		ret = proc_dostring(&table, write, buffer, lenp, ppos);
 		if (ret)
 			return ret;
@@ -74,16 +79,15 @@ int sysctl_sys_info_handler(const struct ctl_table *ro_table, int write,
 		return 0;
 	} else {
 		/* for 'read' operation */
+		unsigned int len = 0;
 		char *delim = "";
-		int i, len = 0;
 
 		/* The access to the global value is not synchronized. */
 		si_bits = READ_ONCE(*si_bits_global);
 
-		names[0] = '\0';
 		for_each_set_bit(i, &si_bits, ARRAY_SIZE(si_names)) {
 			if (*si_names[i]) {
-				len += scnprintf(names + len, sizeof(names) - len,
+				len += scnprintf(names + len, maxlen - len,
 						 "%s%s", delim, si_names[i]);
 				delim = ",";
 			}
@@ -91,7 +95,7 @@ int sysctl_sys_info_handler(const struct ctl_table *ro_table, int write,
 
 		table = *ro_table;
 		table.data = names;
-		table.maxlen = sizeof(names);
+		table.maxlen = maxlen;
 		return proc_dostring(&table, write, buffer, lenp, ppos);
 	}
 }
-- 
2.50.1