On Wed, Dec 14, 2016 at 02:09:27AM +0800, Boqun Feng wrote:
> 2016年12月14日 上午1:17，"Mark Rutland" <[email protected]>写道：
> >
> > Hi,
> >
> > On Tue, Dec 13, 2016 at 10:56:46AM +0000, Colin King wrote:
> > > From: Colin Ian King <[email protected]>
> > >
> > > mask and bit are unsigned longs, so if bit is 31 we end up sign
> > > extending the 1 and mask ends up as 0xffffffff80000000. Fix this
> > > by explicitly adding integer suffix UL ensure 1 is a unsigned long
> > > rather than an signed int.
> > >
> > > Issue found with static analysis with CoverityScan, CID 1388564
> > >
> > > Fixes: 8965c3ce4718754db ("rcu: Use
> leaf_node_for_each_mask_possible_cpu() in force_qs_rnp()")
> > > Signed-off-by: Colin Ian King <[email protected]>
> > > ---
> > > kernel/rcu/tree.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > index 10162ac..6ecedd8 100644
> > > --- a/kernel/rcu/tree.c
> > > +++ b/kernel/rcu/tree.c
> > > @@ -3051,7 +3051,7 @@ static void force_qs_rnp(struct rcu_state *rsp,
> > >
> > > leaf_node_for_each_mask_possible_cpu(rnp, rnp->qsmask,
> bit, cpu)
> > > if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
> > > - mask |= 1 << bit;
> > > + mask |= 1UL << bit;
> >
> > So as to match the rest of the code altered in commit bc75e99983df1efd
> > ("rcu: Correctly handle sparse possible cpus"), and regardless of
> > naming, I think it'd be nicer to use leaf_node_cpu_bit(), e.g.
> >
> > leaf_node_for_each_mask_possible_cpu(rnp, rnp->qsmask, bit, cpu)
> > if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
> > mask |= leaf_node_cpu_bit(rnp, cpu);
> >
> > IMO, it would be nice to hide the iterator bit somehow, to match
> > for_each_leaf_node_possible_cpu(), which this largely looks similar to
> > otherwise.
>
> Good point. ;-)
>
> We can
>
> #define for_each_leaf_node_cpu(rnp, mask, cpu) \
> for((cpu) = (rnp)->grplo + find _first_bit(mask, MASK_BITS(mask)); \
> (cpu) >= (rnp)->grplo && (cpu) <= (rnp)->grphi; \
> (cpu) = (rnp)->grplo + find _next_bit(mask, ...,
> leaf_node_cpu_bit(rnp, cpu) + 1))) \
> if (!cpu_possible(cpu)) \
> continue; \
> else
What is the purpose of the cpu_possible() check?
Thanx, Paul
> Typing from my cellphone, plz ignore the bad formatting ;-)
>
> Regards,
> Boqun
>
> > Thanks,
> > Mark.
