Hi, On Tue, Jun 18, 2019 at 2:14 PM Matthias Kaehlcke <[email protected]> wrote: > > empty_child_inc/dec() use the ternary operator for conditional > operations. The conditions involve the post/pre in/decrement > operator and the operation is only performed when the condition > is *not* true. This is hard to parse for humans, use a regular > 'if' construct instead and perform the in/decrement separately. > > This also fixes two warnings that are emitted about the value > of the ternary expression being unused, when building the kernel > with clang + "kbuild: Remove unnecessary -Wno-unused-value" > (https://lore.kernel.org/patchwork/patch/1089869/): > > CC net/ipv4/fib_trie.o > net/ipv4/fib_trie.c:351:2: error: expression result unused > [-Werror,-Wunused-value] > ++tn_info(n)->empty_children ? : ++tn_info(n)->full_children; > > Signed-off-by: Matthias Kaehlcke <[email protected]> > --- > I have no good understanding of the fib_trie code, but the > disentangled code looks wrong, and it should be equivalent to the > cryptic version, unless I messed it up. In empty_child_inc() > 'full_children' is only incremented when 'empty_children' is -1. I > suspect a bug in the cryptic code, but am surprised why it hasn't > blown up yet. Or is it intended behavior that is just > super-counterintuitive? > > For now I'm leaving it at disentangling the cryptic expressions, > if there is a bug we can discuss what action to take. > --- > net/ipv4/fib_trie.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-)
I have no knowledge of this code either but Matthias's patch looks sane to me and I agree with the disentangling before making functional changes. My own personal belief is that this is pointing out a bug somewhere. Since "empty_children" ends up being an unsigned type it doesn't feel like it was by-design that -1 is ever a value that should be in there. In any case: Reviewed-by: Douglas Anderson <[email protected]>
