panic: sys_info: capture si_bits_global before iterating over it

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>

diff --git a/lib/sys_info.c b/lib/sys_info.c
index 496f9151c9b68c314589301a0beffedce415a0be..d542a024406a5a99092737e69ca09855805bc71d 100644 (file)
--- 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)];
        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 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);
+
                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 = ",";