* [PATCH] iio: frequency: adf4371: Fix divide by zero exception bug
@ 2020-01-07 13:15 Beniamin Bia
2020-01-11 11:08 ` Jonathan Cameron
0 siblings, 1 reply; 4+ messages in thread
From: Beniamin Bia @ 2020-01-07 13:15 UTC (permalink / raw)
To: jic23
Cc: lars, Michael.Hennerich, pmeerw, linux-iio, linux-kernel,
biabeniamin, knaack.h, Michael Hennerich, Beniamin Bia
From: Michael Hennerich <michael.hennerich@analog.com>
During initialization adf4371_pll_fract_n_get_rate() is called on all
output channels to determine if the device was setup. In this case
mod2 is zero which can cause a divide by zero exception.
Return before that can happen.
Fixes: 7f699bd149134 ("iio: frequency: adf4371: Add support for ADF4371 PLL")
Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Beniamin Bia <beniamin.bia@analog.com>
---
drivers/iio/frequency/adf4371.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/iio/frequency/adf4371.c b/drivers/iio/frequency/adf4371.c
index e2a599b912e5..c21462238314 100644
--- a/drivers/iio/frequency/adf4371.c
+++ b/drivers/iio/frequency/adf4371.c
@@ -191,6 +191,9 @@ static unsigned long long adf4371_pll_fract_n_get_rate(struct adf4371_state *st,
unsigned long long val, tmp;
unsigned int ref_div_sel;
+ if (st->mod2 == 0)
+ return 0;
+
val = (((u64)st->integer * ADF4371_MODULUS1) + st->fract1) * st->fpfd;
tmp = (u64)st->fract2 * st->fpfd;
do_div(tmp, st->mod2);
--
2.17.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] iio: frequency: adf4371: Fix divide by zero exception bug
2020-01-07 13:15 [PATCH] iio: frequency: adf4371: Fix divide by zero exception bug Beniamin Bia
@ 2020-01-11 11:08 ` Jonathan Cameron
2020-01-14 16:19 ` Hennerich, Michael
0 siblings, 1 reply; 4+ messages in thread
From: Jonathan Cameron @ 2020-01-11 11:08 UTC (permalink / raw)
To: Beniamin Bia
Cc: lars, Michael.Hennerich, pmeerw, linux-iio, linux-kernel,
biabeniamin, knaack.h
On Tue, 7 Jan 2020 15:15:59 +0200
Beniamin Bia <beniamin.bia@analog.com> wrote:
> From: Michael Hennerich <michael.hennerich@analog.com>
>
> During initialization adf4371_pll_fract_n_get_rate() is called on all
> output channels to determine if the device was setup. In this case
> mod2 is zero which can cause a divide by zero exception.
> Return before that can happen.
I'm confused by this description vs the code.
As far as I can see fract_n_get_rate is only called on a sysfs read of
the frequency.
mod2 is set when fract_n_compute is called in the relevant set_freq calls.
This seems to occur on a sysfs set frequency call.
So the issue here is that a sysfs read before a write of the frequency
will cause a div zero? If so, is there a sane set of initial values we
can put in mod2 and friends before exposing them via the device register?
If mod2==0 is a valid value and indicates for example that the channel
is turned off, then the description should make that clear.
Jonathan
>
> Fixes: 7f699bd149134 ("iio: frequency: adf4371: Add support for ADF4371 PLL")
> Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
> Signed-off-by: Beniamin Bia <beniamin.bia@analog.com>
> ---
> drivers/iio/frequency/adf4371.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/iio/frequency/adf4371.c b/drivers/iio/frequency/adf4371.c
> index e2a599b912e5..c21462238314 100644
> --- a/drivers/iio/frequency/adf4371.c
> +++ b/drivers/iio/frequency/adf4371.c
> @@ -191,6 +191,9 @@ static unsigned long long adf4371_pll_fract_n_get_rate(struct adf4371_state *st,
> unsigned long long val, tmp;
> unsigned int ref_div_sel;
>
> + if (st->mod2 == 0)
> + return 0;
> +
> val = (((u64)st->integer * ADF4371_MODULUS1) + st->fract1) * st->fpfd;
> tmp = (u64)st->fract2 * st->fpfd;
> do_div(tmp, st->mod2);
^ permalink raw reply [flat|nested] 4+ messages in thread
* RE: [PATCH] iio: frequency: adf4371: Fix divide by zero exception bug
2020-01-11 11:08 ` Jonathan Cameron
@ 2020-01-14 16:19 ` Hennerich, Michael
2020-01-18 11:29 ` Jonathan Cameron
0 siblings, 1 reply; 4+ messages in thread
From: Hennerich, Michael @ 2020-01-14 16:19 UTC (permalink / raw)
To: Jonathan Cameron, Bia, Beniamin
Cc: lars, pmeerw, linux-iio, linux-kernel, biabeniamin, knaack.h
> -----Original Message-----
> From: Jonathan Cameron <jic23@kernel.org>
> Sent: Samstag, 11. Januar 2020 12:09
> To: Bia, Beniamin <Beniamin.Bia@analog.com>
> Cc: lars@metafoo.de; Hennerich, Michael <Michael.Hennerich@analog.com>;
> pmeerw@pmeerw.net; linux-iio@vger.kernel.org; linux-
> kernel@vger.kernel.org; biabeniamin@outlook.com; knaack.h@gmx.de
> Subject: Re: [PATCH] iio: frequency: adf4371: Fix divide by zero exception bug
>
> On Tue, 7 Jan 2020 15:15:59 +0200
> Beniamin Bia <beniamin.bia@analog.com> wrote:
>
> > From: Michael Hennerich <michael.hennerich@analog.com>
> >
> > During initialization adf4371_pll_fract_n_get_rate() is called on all
> > output channels to determine if the device was setup. In this case
> > mod2 is zero which can cause a divide by zero exception.
> > Return before that can happen.
> I'm confused by this description vs the code.
>
> As far as I can see fract_n_get_rate is only called on a sysfs read of the
> frequency.
That's not the case. The failure mechanism comes via adf4371_channel_config().
It calls adf4371_pll_fract_n_get_rate() prior adf4371_set_freq() which initializes
st->mod2 via adf4371_pll_fract_n_compute(). This only happens the first time
during probe and setup. So the solution was to return 0 if st->mod2 == 0.
-Michael
>
> mod2 is set when fract_n_compute is called in the relevant set_freq calls.
> This seems to occur on a sysfs set frequency call.
>
> So the issue here is that a sysfs read before a write of the frequency will cause a
> div zero? If so, is there a sane set of initial values we can put in mod2 and
> friends before exposing them via the device register?
>
> If mod2==0 is a valid value and indicates for example that the channel is turned
> off, then the description should make that clear.
>
> Jonathan
>
> >
> > Fixes: 7f699bd149134 ("iio: frequency: adf4371: Add support for
> > ADF4371 PLL")
> > Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
> > Signed-off-by: Beniamin Bia <beniamin.bia@analog.com>
> > ---
> > drivers/iio/frequency/adf4371.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/iio/frequency/adf4371.c
> > b/drivers/iio/frequency/adf4371.c index e2a599b912e5..c21462238314
> > 100644
> > --- a/drivers/iio/frequency/adf4371.c
> > +++ b/drivers/iio/frequency/adf4371.c
> > @@ -191,6 +191,9 @@ static unsigned long long
> adf4371_pll_fract_n_get_rate(struct adf4371_state *st,
> > unsigned long long val, tmp;
> > unsigned int ref_div_sel;
> >
> > + if (st->mod2 == 0)
> > + return 0;
> > +
> > val = (((u64)st->integer * ADF4371_MODULUS1) + st->fract1) * st-
> >fpfd;
> > tmp = (u64)st->fract2 * st->fpfd;
> > do_div(tmp, st->mod2);
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] iio: frequency: adf4371: Fix divide by zero exception bug
2020-01-14 16:19 ` Hennerich, Michael
@ 2020-01-18 11:29 ` Jonathan Cameron
0 siblings, 0 replies; 4+ messages in thread
From: Jonathan Cameron @ 2020-01-18 11:29 UTC (permalink / raw)
To: Hennerich, Michael
Cc: Bia, Beniamin, lars, pmeerw, linux-iio, linux-kernel,
biabeniamin, knaack.h
On Tue, 14 Jan 2020 16:19:28 +0000
"Hennerich, Michael" <Michael.Hennerich@analog.com> wrote:
> > -----Original Message-----
> > From: Jonathan Cameron <jic23@kernel.org>
> > Sent: Samstag, 11. Januar 2020 12:09
> > To: Bia, Beniamin <Beniamin.Bia@analog.com>
> > Cc: lars@metafoo.de; Hennerich, Michael <Michael.Hennerich@analog.com>;
> > pmeerw@pmeerw.net; linux-iio@vger.kernel.org; linux-
> > kernel@vger.kernel.org; biabeniamin@outlook.com; knaack.h@gmx.de
> > Subject: Re: [PATCH] iio: frequency: adf4371: Fix divide by zero exception bug
> >
> > On Tue, 7 Jan 2020 15:15:59 +0200
> > Beniamin Bia <beniamin.bia@analog.com> wrote:
> >
> > > From: Michael Hennerich <michael.hennerich@analog.com>
> > >
> > > During initialization adf4371_pll_fract_n_get_rate() is called on all
> > > output channels to determine if the device was setup. In this case
> > > mod2 is zero which can cause a divide by zero exception.
> > > Return before that can happen.
> > I'm confused by this description vs the code.
> >
> > As far as I can see fract_n_get_rate is only called on a sysfs read of the
> > frequency.
>
> That's not the case. The failure mechanism comes via adf4371_channel_config().
> It calls adf4371_pll_fract_n_get_rate() prior adf4371_set_freq() which initializes
> st->mod2 via adf4371_pll_fract_n_compute(). This only happens the first time
> during probe and setup. So the solution was to return 0 if st->mod2 == 0.
Not in mainline it doesn't. I took a look at the ADI git hub and I see it does
there. I think we are missing a precursor patch.
Probably this one from blame...
https://github.com/analogdevicesinc/linux/commit/c8e6b341abf749f78e00326cb92b365d90d9de1f
Jonathan
>
> -Michael
>
> >
> > mod2 is set when fract_n_compute is called in the relevant set_freq calls.
> > This seems to occur on a sysfs set frequency call.
> >
> > So the issue here is that a sysfs read before a write of the frequency will cause a
> > div zero? If so, is there a sane set of initial values we can put in mod2 and
> > friends before exposing them via the device register?
> >
> > If mod2==0 is a valid value and indicates for example that the channel is turned
> > off, then the description should make that clear.
> >
> > Jonathan
> >
> > >
> > > Fixes: 7f699bd149134 ("iio: frequency: adf4371: Add support for
> > > ADF4371 PLL")
> > > Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
> > > Signed-off-by: Beniamin Bia <beniamin.bia@analog.com>
> > > ---
> > > drivers/iio/frequency/adf4371.c | 3 +++
> > > 1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/iio/frequency/adf4371.c
> > > b/drivers/iio/frequency/adf4371.c index e2a599b912e5..c21462238314
> > > 100644
> > > --- a/drivers/iio/frequency/adf4371.c
> > > +++ b/drivers/iio/frequency/adf4371.c
> > > @@ -191,6 +191,9 @@ static unsigned long long
> > adf4371_pll_fract_n_get_rate(struct adf4371_state *st,
> > > unsigned long long val, tmp;
> > > unsigned int ref_div_sel;
> > >
> > > + if (st->mod2 == 0)
> > > + return 0;
> > > +
> > > val = (((u64)st->integer * ADF4371_MODULUS1) + st->fract1) * st-
> > >fpfd;
> > > tmp = (u64)st->fract2 * st->fpfd;
> > > do_div(tmp, st->mod2);
>
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2020-01-18 11:29 UTC | newest]
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2020-01-07 13:15 [PATCH] iio: frequency: adf4371: Fix divide by zero exception bug Beniamin Bia
2020-01-11 11:08 ` Jonathan Cameron
2020-01-14 16:19 ` Hennerich, Michael
2020-01-18 11:29 ` Jonathan Cameron
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