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 <[email protected]>
Acked-by: Randy Dunlap <[email protected]> # build-tested
Signed-off-by: Larry Finger <[email protected]>
---
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);
--
2.38.0
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 <[email protected]>
> Acked-by: Randy Dunlap <[email protected]> # build-tested
> Signed-off-by: Larry Finger <[email protected]>
> ---
> 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 <[email protected]>