| Message ID | 20221104012750.2076-1-Larry.Finger@lwfinger.net (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | Johannes Berg |
| Headers | show |
| Series | [v2] staging: rtl8192e: Fix divide fault when calculating beacon age | expand |
On 11/4/22 02:27, Larry Finger wrote: > 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> > --- > v2 - some commit log lines are shortened > - add space after * operator > --- > drivers/staging/rtl8192e/rtllib_wx.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/staging/rtl8192e/rtllib_wx.c b/drivers/staging/rtl8192e/rtllib_wx.c > index da2c41c9b92f..217426ee2e92 100644 > --- 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); Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
diff --git a/drivers/staging/rtl8192e/rtllib_wx.c b/drivers/staging/rtl8192e/rtllib_wx.c index da2c41c9b92f..217426ee2e92 100644 --- 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);
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> --- v2 - some commit log lines are shortened - add space after * operator --- drivers/staging/rtl8192e/rtllib_wx.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)