+ panic-sys_info-capture-si_bits_global-before-iterating-over-it.patch added to mm-nonmm-unstable branch

+ panic-sys_info-capture-si_bits_global-before-iterating-over-it.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: panic: sys_info: capture si_bits_global before iterating over it
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     panic-sys_info-capture-si_bits_global-before-iterating-over-it.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/panic-sys_info-capture-si_bits_global-before-iterating-over-it.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Subject: panic: sys_info: capture si_bits_global before iterating over it
Date: Thu, 30 Oct 2025 12:44:17 +0100

Patch series "panic: sys_info: Refactor and fix a potential issue", v3.

While targeting the compilation issue due to dangling variable, I have
noticed more opportunities for refactoring that helps to avoid above
mentioned compilation issue in a cleaner way and also fixes a potential
problem with global variable access.


This patch (of 6):

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.

Link: https://lkml.kernel.org/r/20251030132007.3742368-1-andriy.shevchenko@linux.intel.com
Link: https://lkml.kernel.org/r/20251030132007.3742368-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Feng Tang <feng.tang@linux.alibaba.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/sys_info.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/lib/sys_info.c~panic-sys_info-capture-si_bits_global-before-iterating-over-it
+++ a/lib/sys_info.c
@@ -58,11 +58,11 @@ int sysctl_sys_info_handler(const struct
 	char names[sizeof(sys_info_avail)];
 	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;
@@ -81,9 +81,12 @@ int sysctl_sys_info_handler(const struct
 		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 (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 = ",";
_

Patches currently in -mm which might be from andriy.shevchenko@linux.intel.com are

panic-sys_info-capture-si_bits_global-before-iterating-over-it.patch
panic-sys_info-align-constant-definition-names-with-parameters.patch
panic-sys_info-replace-struct-sys_info_name-with-plain-array-of-strings.patch
panic-sys_info-rewrite-a-fix-for-a-compilation-error-make-w=1.patch
panic-sys_info-deduplicate-local-variable-table-assignments.patch
panic-sys_info-factor-out-read-and-write-handlers.patch