On Sun, Sep 21, 2025 at 09:49:54AM +0200, Thomas Gleixner wrote:
> On Tue, Sep 16 2025 at 03:19, Wake Liu wrote:
> > The timespec_sub function, as implemented in several timer
>
> timespec_sub()
>
> https://www.kernel.org/doc/html/latest/process/maintainer-tip.html#function-references-in-changelogs
>
> > selftests, is prone to integer overflow on 32-bit systems.
> >
> > The calculation `NSEC_PER_SEC * b.tv_sec` is performed using
> > 32-bit arithmetic, and the result overflows before being
> > stored in the 64-bit `ret` variable. This leads to incorrect
> > time delta calculations and test failures.
> >
> > As suggested by tglx, this patch fixes the issue by:
>
> s/this patch fixes/fix/
>
>
>
> > 1. Creating a new `static inline` helper function,
> > `timespec_to_ns`, which safely converts a `timespec` to
> > nanoseconds by casting `tv_sec` to `long long` before
> > multiplying with `NSEC_PER_SEC`.
> >
> > 2. Placing the new helper and a rewritten `timespec_sub` into
> > a common header: tools/testing/selftests/timers/helpers.h.
> >
> > 3. Removing the duplicated, buggy implementations from all
> > timer selftests and replacing them with an #include of the
> > new header.
> >
> > This consolidates the code and ensures the calculation is
> > correctly performed using 64-bit arithmetic across all tests.
>
> This lacks a Signed-off-by.
>
> > Changes in v2:
> > - Per tglx's feedback, instead of changing NSEC_PER_SEC globally,
> > this version consolidates the buggy timespec_sub() implementations
> > into a new 32-bit safe inline function in a shared header.
> > - Amended the commit message to be more descriptive.
>
> change logs go behind the '---' separator as they are not part of the
> commit message. It's documented how to format a change log properly.
>
> > -#define UNREASONABLE_LAT (NSEC_PER_SEC * 5) /* hopefully we resume in 5
> > secs */
> > +#define UNREASONABLE_LAT (NSEC_PER_SEC * 5LL) /* hopefully we resume in 5
> > secs */
>
> How is this change and the pile of similar ones related to $subject and
> why are they required in the first place?
>
> > index 000000000000..652f20247091
> > --- /dev/null
> > +++ b/tools/testing/selftests/timers/helpers.h
> > @@ -0,0 +1,31 @@
>
> Lacks a SPDX identifier.
>
> scripts/checkpatch.pl exists for a reason.
>
> Thanks,
>
> tglx
I also just stumbled into this. However, doing a little bit of research
it seems this was introduced by commit 80fa614e2fbc ("selftests: timers:
Remove local NSEC_PER_SEC and USEC_PER_SEC defines"), which explicitly
changes the local definitions in favor of the internal kernel header,
but that doesn't seem right.
I think we should probably revert that commit instead?
--
Carlos Llamas
