From: Wei Yang <[email protected]> There is only 1 bit set in mask, which means that the only difference between oldmask and the new one will be at the position where the bit is set in mask. This commit therefore updates rcu_state.ncpus by checking whether the bit in mask is already set in rnp->expmaskinitnext.
Signed-off-by: Wei Yang <[email protected]> Signed-off-by: Paul E. McKenney <[email protected]> --- kernel/rcu/tree.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index c716ead..9caaeee 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3824,10 +3824,9 @@ void rcu_cpu_starting(unsigned int cpu) { unsigned long flags; unsigned long mask; - int nbits; - unsigned long oldmask; struct rcu_data *rdp; struct rcu_node *rnp; + bool newcpu; if (per_cpu(rcu_cpu_started, cpu)) return; @@ -3839,12 +3838,10 @@ void rcu_cpu_starting(unsigned int cpu) mask = rdp->grpmask; raw_spin_lock_irqsave_rcu_node(rnp, flags); WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask); - oldmask = rnp->expmaskinitnext; + newcpu = !(rnp->expmaskinitnext & mask); rnp->expmaskinitnext |= mask; - oldmask ^= rnp->expmaskinitnext; - nbits = bitmap_weight(&oldmask, BITS_PER_LONG); /* Allow lockless access for expedited grace periods. */ - smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + nbits); /* ^^^ */ + smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + newcpu); /* ^^^ */ ASSERT_EXCLUSIVE_WRITER(rcu_state.ncpus); rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */ rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq); -- 2.9.5
