| Message ID | 20210923082319.1510936-1-drhunter95@gmail.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | [v2] workaround regression in ina2xx introduced by cb47755725da("time: Prevent undefined behaviour in timespec64_to_ns()") | expand |
On Thu, 23 Sep 2021 09:23:16 +0100 Iain Hunter <drhunter95@gmail.com> wrote: > From: Iain Hunter <iain@hunterembedded.co.uk> > > That change adds an error check to avoid saturation during multiplication > to calculate nano seconds in timespec64_to_ns(). This function was changed > in kernel 5.4. > In ina2xx_capture_thread() a timespec64 structure is used to calculate > the delta time until the next sample time. This delta can be negative if > the next sample time was in the past. In the -1 case timespec64_to_ns() > now clamps the -1 second value to KTIME_MAX. This essentially puts ina2xx > thread to sleep forever. > Proposed patch is to split the functionality in the loop into two parts: > - do while loop only does the test to see if the next sample time is in > the future or in the past and so will be skipped and the sample time > incremented until it is in the future. This comparision can be done with > timespec64_compare() as we are only interested in the sign being positive > or negative. > The variable skip_next_sample is only used for clarity. > - after do while loop we know that next is later than now and so delta is > guaranteed to be positive. This means timespec64_to_ns() can be safely > used. > > Signed-off-by: Iain Hunter <iain@hunterembedded.co.uk> > > Fixes: regression introduced by > cb47755725da("time: Prevent undefined behaviour in timespec64_to_ns()") Please check how to format a fixes tag. As they are used in automated tooling it must be exactly what is documented in https://www.kernel.org/doc/Documentation/process/submitting-patches.rst Approach looks sound but I think we can simplify things a little. > --- > drivers/iio/adc/ina2xx-adc.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c > index a4b2ff9e0..e30012d0d 100644 > --- a/drivers/iio/adc/ina2xx-adc.c > +++ b/drivers/iio/adc/ina2xx-adc.c > @@ -777,6 +777,7 @@ static int ina2xx_capture_thread(void *data) > int ret; > struct timespec64 next, now, delta; > s64 delay_us; > + int skip_next_sample; > > /* > * Poll a bit faster than the chip internal Fs, in case > @@ -817,10 +818,15 @@ static int ina2xx_capture_thread(void *data) > */ > do { > timespec64_add_ns(&next, 1000 * sampling_us); > - delta = timespec64_sub(next, now); > - delay_us = div_s64(timespec64_to_ns(&delta), 1000); > - } while (delay_us <= 0); > > + if (timespec64_compare(&next, &now) < 0) > + skip_next_sample = 1; > + else > + skip_next_sample = 0; > + } while (skip_next_sample); the local variable doesn't add much and should be a boolean given it can only take true or false. do { timespec64_add_ns(&next, 1000 * sampling_us); } while (timespec64_compare(&next, &now) < 0); Is probably the neatest option. > + > + delta = timespec64_sub(next, now); > + delay_us = div_s64(timespec64_to_ns(&delta), 1000); > usleep_range(delay_us, (delay_us * 3) >> 1); > > } while (!kthread_should_stop());
diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c index a4b2ff9e0..e30012d0d 100644 --- a/drivers/iio/adc/ina2xx-adc.c +++ b/drivers/iio/adc/ina2xx-adc.c @@ -777,6 +777,7 @@ static int ina2xx_capture_thread(void *data) int ret; struct timespec64 next, now, delta; s64 delay_us; + int skip_next_sample; /* * Poll a bit faster than the chip internal Fs, in case @@ -817,10 +818,15 @@ static int ina2xx_capture_thread(void *data) */ do { timespec64_add_ns(&next, 1000 * sampling_us); - delta = timespec64_sub(next, now); - delay_us = div_s64(timespec64_to_ns(&delta), 1000); - } while (delay_us <= 0); + if (timespec64_compare(&next, &now) < 0) + skip_next_sample = 1; + else + skip_next_sample = 0; + } while (skip_next_sample); + + delta = timespec64_sub(next, now); + delay_us = div_s64(timespec64_to_ns(&delta), 1000); usleep_range(delay_us, (delay_us * 3) >> 1); } while (!kthread_should_stop());