From: Ulrich Hecht <uli@fpond.eu>
To: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
sergei.shtylyov@gmail.com, davem@davemloft.net, kuba@kernel.org
Cc: netdev@vger.kernel.org, linux-renesas-soc@vger.kernel.org
Subject: Re: [PATCH 1/2] ravb: Fix descriptor counters' conditions
Date: Tue, 27 Jul 2021 11:13:55 +0200 (CEST) [thread overview]
Message-ID: <1863500318.822017.1627377235170@webmail.strato.com> (raw)
In-Reply-To: <1879319092.816143.1627376136422@webmail.strato.com>
> On 07/27/2021 10:55 AM Ulrich Hecht <uli@fpond.eu> wrote:
>
>
> > On 07/27/2021 10:21 AM Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com> wrote:
> >
> >
> > The descriptor counters ({cur,dirty}_[rt]x) acts as free counters
> > so that conditions are possible to be incorrect when a left value
> > was overflowed.
> >
> > So, for example, ravb_tx_free() could not free any descriptors
> > because the following condition was checked as a signed value,
> > and then "NETDEV WATCHDOG" happened:
> >
> > for (; priv->cur_tx[q] - priv->dirty_tx[q] > 0; priv->dirty_tx[q]++) {
> >
> > To fix the issue, add get_num_desc() to calculate numbers of
> > remaining descriptors.
> >
> > Fixes: c156633f1353 ("Renesas Ethernet AVB driver proper")
> > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
> > ---
> > drivers/net/ethernet/renesas/ravb_main.c | 22 +++++++++++++++-------
> > 1 file changed, 15 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> > index 805397088850..70fbac572036 100644
> > --- a/drivers/net/ethernet/renesas/ravb_main.c
> > +++ b/drivers/net/ethernet/renesas/ravb_main.c
> > @@ -172,6 +172,14 @@ static const struct mdiobb_ops bb_ops = {
> > .get_mdio_data = ravb_get_mdio_data,
> > };
> >
> > +static u32 get_num_desc(u32 from, u32 subtract)
> > +{
> > + if (from >= subtract)
> > + return from - subtract;
> > +
> > + return U32_MAX - subtract + 1 + from;
> > +}
>
> This is a very roundabout way to implement an unsigned subtraction. :)
> I think it would make more sense to simply return 0 if "subtract" is larger than "from".
> (Likewise for sh_eth).
...and the tests for "> 0" should be rewritten as "!= 0". Sorry, not fully awake yet.
CU
Uli
next prev parent reply other threads:[~2021-07-27 9:13 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-27 8:21 [PATCH 0/2] ravb and sh_eth: Fix descriptor counters' conditions Yoshihiro Shimoda
2021-07-27 8:21 ` [PATCH 1/2] ravb: " Yoshihiro Shimoda
2021-07-27 8:55 ` Ulrich Hecht
2021-07-27 9:13 ` Ulrich Hecht [this message]
2021-07-27 9:52 ` Yoshihiro Shimoda
2021-07-27 8:21 ` [PATCH 2/2] sh_eth: " Yoshihiro Shimoda
2021-07-29 4:59 ` [PATCH 0/2] ravb and " Yoshihiro Shimoda
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1863500318.822017.1627377235170@webmail.strato.com \
--to=uli@fpond.eu \
--cc=davem@davemloft.net \
--cc=kuba@kernel.org \
--cc=linux-renesas-soc@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=sergei.shtylyov@gmail.com \
--cc=yoshihiro.shimoda.uh@renesas.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).