On Wed, May 18, 2016 at 11:01:53AM -0700, Paul E. McKenney wrote: > On Wed, May 18, 2016 at 06:15:23PM +0300, Andrey Ryabinin wrote: > > 2016-05-16 19:48 GMT+03:00 Mark Rutland <mark.rutl...@arm.com>: > > > > > /* > > > + * Iterate over all possible CPUs in a leaf RCU node. > > > + */ > > > +#define for_each_leaf_node_possible_cpu(rnp, cpu) \ > > > + for ((cpu) = rnp->grplo; \ > > > + cpu <= rnp->grphi; \ > > > + cpu = cpumask_next((cpu), cpu_possible_mask)) > > > + > > > +/* > > > + * Iterate over all possible CPUs in a leaf RCU node, at each step > > > providing a > > > + * bit for comparison against rcu_node bitmasks. > > > + */ > > > +#define for_each_leaf_node_possible_cpu_bit(rnp, cpu, bit) \ > > > + for ((cpu) = rnp->grplo, (bit) = 1; \ > > > + cpu <= rnp->grphi; \ > > > + cpu = cpumask_next((cpu), cpu_possible_mask), \ > > > + (bit) = 1UL << (cpu - rnp->grplo)) > > > + > > > > [ 0.163652] UBSAN: Undefined behaviour in ../kernel/rcu/tree.c:2912:3 > > [ 0.164000] shift exponent 64 is too large for 64-bit type 'long > > unsigned int' > > Ah, dead value, but can happen nevertheless. One fix is to prevent the > assignment to bit when cpu > rnp->grphi. > > Any ideas for a better fix? And isn't there some combination of > signedness that makes shifting all the bits out of the value defined > to zero? Or is that only for right shifts?
We could add a (leaf/rcu)_node_cpu_mask(rnp, cpu) macro, and only use that in the body of the loop. That would avoid the stale value and would be useful in a couple of additional places. If that makes sense to you, I can respin the patch with that. Thanks, Mark.
