Commit bb5b5e21 authored by Larry Finger's avatar Larry Finger Committed by Greg Kroah-Hartman
Browse files

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: default avatarRandy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Signed-off-by: default avatarLarry Finger <Larry.Finger@lwfinger.net>
Tested-by: default avatarPhilipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/20221104012750.2076-1-Larry.Finger@lwfinger.net


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent dcb18f51

drivers/staging/rtl8192e/rtllib_wx.c

+3 −3
Original line number Diff line number Diff line
@@ -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);