On Tue, Jun 18, 2019 at 02:45:34PM -0700, Doug Anderson wrote: > 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.
I in terms of the -stable process it might make sense to either disentangle & fix in a single step, or first fix the cryptic code (shudder!) and then disentangle it. I guess if we make it a series disentangle & fix could be separate steps. I'm open to whatever maintainers & stable folks prefer. > 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. good point that 'empty_children' is unsigned, that indeed reinforces the bug theory. > In any case: > > Reviewed-by: Douglas Anderson <[email protected]> Thanks!
