staging: rtl8192e: Fix divide fault when calculating beacon age

When the configuration parameter CONFIG_HZ is less that 100, the compiler
generates an error as follows:

../drivers/staging/rtl8192e/rtllib_wx.c: In function 'rtl819x_translate_scan':
../drivers/staging/rtl8192e/rtllib_wx.c:220:57: warning: division by zero [-Wdiv-by-zero]
  220 |      (jiffies - network->last_scanned) / (HZ / 100));
      |                                                         ^
In file included from ../include/linux/skbuff.h:45,
                 from ../include/linux/if_ether.h:19,
                 from ../include/linux/etherdevice.h:20,
                 from ../drivers/staging/rtl8192e/rtllib_wx.c:18:
../drivers/staging/rtl8192e/rtllib_wx.c: In function 'rtllib_wx_get_scan':
../drivers/staging/rtl8192e/rtllib_wx.c:261:70: warning: division by zero [-Wdiv-by-zero]
  261 |      (jiffies - network->last_scanned) /
      |

In fact, is HZ is not a multiple of 100, the calculation will be wrong,
but it will compile correctly.

The fix is to get rid of the (HZ / 100) portion. To decrease any round-off
errors, the compiler is forced to perform the 100 * jiffies-difference
before dividing by HZ. This patch is only compile tested.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/20221104012750.2076-1-Larry.Finger@lwfinger.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/rtl8192e/rtllib_wx.c b/drivers/staging/rtl8192e/rtllib_wx.c
index da2c41c9b92f1ff4e5850cffc2ba1b33bdd49cb1..217426ee2e92a5b61120a9da6d78e6722c56726a 100644 (file)
--- a/drivers/staging/rtl8192e/rtllib_wx.c
+++ b/drivers/staging/rtl8192e/rtllib_wx.c
@@ -217,7 +217,7 @@ static inline char *rtl819x_translate_scan(struct rtllib_device *ieee,
        p = custom;
        p += scnprintf(p, MAX_CUSTOM_LEN - (p - custom),
                      " Last beacon: %lums ago",
-                     (jiffies - network->last_scanned) / (HZ / 100));
+                     (100 * (jiffies - network->last_scanned)) / HZ);
        iwe.u.data.length = p - custom;
        if (iwe.u.data.length)
                start = iwe_stream_add_point_rsl(info, start, stop,
@@ -258,8 +258,8 @@ int rtllib_wx_get_scan(struct rtllib_device *ieee,
                                   escape_essid(network->ssid,
                                                network->ssid_len),
                                   network->bssid,
-                                  (jiffies - network->last_scanned) /
-                                  (HZ / 100));
+                                  (100 * (jiffies - network->last_scanned)) /
+                                  HZ);
        }
 
        spin_unlock_irqrestore(&ieee->lock, flags);