Re: [PATCH] net/ixgbe: fix inverted test and set conditional

[Tyler Retzlaff <roretzla@linux.microsoft.com>]

On Mon, Jun 19, 2023 at 10:19:00AM +0200, Morten Brørup wrote:
> > From: David Marchand [mailto:david.marchand@redhat.com]
> > Sent: Monday, 19 June 2023 09.54
> > 
> > On Thu, Jun 15, 2023 at 9:30 PM Tyler Retzlaff
> > <roretzla@linux.microsoft.com> wrote:
> > >
> > > Correct a mistake when converting ixgbe to use __atomic_test_and_set
> > > instead of rte_atomic32_test_and_set. The return value from
> > > __atomic_test_and_set is inverted relative to rte_atomic32_test_and_set.
> > >
> > > Fixes: e90baf6b82f6 ("net/ixgbe: replace legacy atomics with GCC builtin
> > atomics")
> > >
> > > Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> > Reviewed-by: David Marchand <david.marchand@redhat.com>
> > 
> > Thanks for the fix Tyler.
> 
> rte_atomic32_test_and_set() returns the inverse of __atomic_test_and_set()!
> 
> We need to provide a prominent warning about this when deprecating rte_atomic32_test_and_set(), or everyone else will make the same mistake as Tyler, i.e. perform a simple search/replace with the new function name, not noticing that the function's return value is inverted.
> Perhaps we can also add some build time warning when using rte_atomic32_test_and_set()?

i'll probably take care of this work myself after stdatomics (assuming
it is something people want) and hopefully i won't make that mistake
again. for now i don't want to confuse the dev list with too many
patches about 'atomics' to avoid overload/confusion for david and thomas.

> 
> PS:
> Tyler, the Solarflare driver also uses rte_atomic32_test_and_set(); maybe you missed in the original patch series.

it was intentionally skipped (for now). i only did the conversion for
drivers that are built on windows. the assumption being the rte_atomicXX
api deprecation is independent of switching to C11 stdatomic.

i don't intend to ever make available rte_atomicXX on msvc/windows
combination since it is being deprecated. as mentioned above as i expand
the code that is built for msvc/windows it will then force me to adapt
more of the rte_atomicsXX code eventually leading to most of it being
gone (at least for libraries).

> https://elixir.bootlin.com/dpdk/v23.07-rc1/A/ident/rte_atomic32_test_and_set
>