2022-02-09 13:53:59

by 王擎

Subject: [PATCH] net: wireless: ath: use div64_u64() instead of do_div()

From: Wang Qing <[email protected]>

do_div() does a 64-by-32 division.
When the divisor is u64, do_div() truncates it to 32 bits, this means it
can test non-zero and be truncated to zero for division.

fix do_div.cocci warning:
do_div() does a 64-by-32 division, please consider using div64_u64 instead.

Signed-off-by: Wang Qing <[email protected]>
---
drivers/net/wireless/ath/wil6210/debugfs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireless/ath/wil6210/debugfs.c b/drivers/net/wireless/ath/wil6210/debugfs.c
index 4c944e5..2cee9dd
--- a/drivers/net/wireless/ath/wil6210/debugfs.c
+++ b/drivers/net/wireless/ath/wil6210/debugfs.c
@@ -1766,7 +1766,7 @@ __acquires(&p->tid_rx_lock) __releases(&p->tid_rx_lock)
seq_puts(s, "\n");
if (!num_packets)
continue;
- do_div(tx_latency_avg, num_packets);
+ div64_u64(tx_latency_avg, num_packets);
seq_printf(s, "Tx/Latency min/avg/max (us): %d/%lld/%d",
p->stats.tx_latency_min_us,
tx_latency_avg,
--
2.7.4

2022-02-10 07:30:07

by Kalle Valo

Subject: Re: [PATCH] net: wireless: ath: use div64_u64() instead of do_div()

Qing Wang <[email protected]> writes:

> From: Wang Qing <[email protected]>
>
> do_div() does a 64-by-32 division.
> When the divisor is u64, do_div() truncates it to 32 bits, this means it
> can test non-zero and be truncated to zero for division.
>
> fix do_div.cocci warning:
> do_div() does a 64-by-32 division, please consider using div64_u64 instead.
>
> Signed-off-by: Wang Qing <[email protected]>
> ---
> drivers/net/wireless/ath/wil6210/debugfs.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

The subject prefix should be "wil6210:", but I can fix that.

--
https://patchwork.kernel.org/project/linux-wireless/list/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches

2022-02-11 13:31:16

by David Laight

Subject: RE: [PATCH] net: wireless: ath: use div64_u64() instead of do_div()

From: Kalle Valo
> Sent: 10 February 2022 12:16
>
> Qing Wang <[email protected]> writes:
>
> > From: Wang Qing <[email protected]>
> >
> > do_div() does a 64-by-32 division.
> > When the divisor is u64, do_div() truncates it to 32 bits, this means it
> > can test non-zero and be truncated to zero for division.
> >
> > fix do_div.cocci warning:
> > do_div() does a 64-by-32 division, please consider using div64_u64 instead.
> >
> > Signed-off-by: Wang Qing <[email protected]>
> > ---
> > drivers/net/wireless/ath/wil6210/debugfs.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/wireless/ath/wil6210/debugfs.c b/drivers/net/wireless/ath/wil6210/debugfs.c
> > index 4c944e5..2cee9dd
> > --- a/drivers/net/wireless/ath/wil6210/debugfs.c
> > +++ b/drivers/net/wireless/ath/wil6210/debugfs.c
> > @@ -1766,7 +1766,7 @@ __acquires(&p->tid_rx_lock) __releases(&p->tid_rx_lock)
> > seq_puts(s, "\n");
> > if (!num_packets)
> > continue;
> > - do_div(tx_latency_avg, num_packets);
> > + div64_u64(tx_latency_avg, num_packets);
>
> As you have been pointed out in your other patches, do_div() and
> div64_u64() work differently.

And how long does it take for num_packets to exceed 2^32.

David

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