linux-kernel - Re: [PATCH] pwm: Zero-initialize the pwm_state passed to driver's .get

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Date:   Tue, 28 Feb 2023 22:48:18 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Munehisa Kamata <kamatam@...zon.com>
Cc:     linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, thierry.reding@...il.com,
        kernel@...gutronix.de, tobetter@...il.com
Subject: Re: [PATCH] pwm: Zero-initialize the pwm_state passed to driver's
 .get_state()

Hello,

On Tue, Feb 28, 2023 at 11:43:27AM -0800, Munehisa Kamata wrote:
> On Tue, 2023-02-28 10:15:58 +0000, Uwe Kleine-König wrote:
> >
> > This is just to ensure that .usage_power is properly initialized and
> > doesn't contain random stack data. The other members of struct pwm_state
> > should get a value assigned in a successful call to .get_state(). So in
> > the absence of bugs in driver implementations, this is only a safe-guard
> > and no fix.
> > 
> > Reported-by: Munehisa Kamata <kamatam@...zon.com>
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > ---
> >  drivers/pwm/core.c | 9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> > 
> > Hello,
> > 
> > On Sat, Feb 25, 2023 at 05:37:21PM -0800, Munehisa Kamata wrote:
> > > Zero-initialize the on-stack structure to avoid unexpected behaviors. Some
> > > drivers may not set or initialize all the values in pwm_state through their
> > > .get_state() callback and therefore some random values may remain there and
> > > be set into pwm->state eventually.
> > > 
> > > This actually caused regression on ODROID-N2+ as reported in [1]; kernel
> > > fails to boot due to random panic or hang-up.
> > > 
> > > [1] https://forum.odroid.com/viewtopic.php?f=177&t=46360
> > > 
> > > Fixes: c73a3107624d ("pwm: Handle .get_state() failures")
> > > Cc: stable@...r.kernel.org # 6.2
> > > Signed-off-by: Munehisa Kamata <kamatam@...zon.com>
> > 
> > My patch is essentially the same as Munehisa's, just written a bit
> > differently (to maybe make it easier for the compiler to optimize it?)
> > and with an explaining comment. The actual motivation is different so
> > the commit log is considerably different, too.
> > 
> > I was unsure how to honor Munehisa's effort, I went with a
> > "Reported-by". Please tell me if you want this to be different.
> 
> I'm okay with that, thank you.
> 
> Perhaps, you should also add Cc tag for the stable tree? I did that in my
> patch and we're actually CCing to the stable list, but I'm not sure if it
> can pick up your patch without the tag. This should be fixed in linux-6.2.y.

IMHO the problem you reported should be fixed by adapting .get_state()
in the meson driver.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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