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@amazon.com Signed-off-by: Uwe Kleine-König u.kleine-koenig@pengutronix.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@vger.kernel.org # 6.2 Signed-off-by: Munehisa Kamata kamatam@amazon.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