Messages in this thread | | | Date | Tue, 4 Sep 2012 15:51:53 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 10/15] rcu: Protect rcu_node accesses during CPU stall warnings |
| |
On Fri, Aug 31, 2012 at 11:23:02AM -0700, Josh Triplett wrote: > On Thu, Aug 30, 2012 at 11:56:23AM -0700, Paul E. McKenney wrote: > > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > > > > The print_other_cpu_stall() function accesses a number of rcu_node > > fields without protection from the ->lock. In theory, this is not > > a problem because the fields accessed are all integers, but in > > practice the compiler can get nasty. Therefore, the commit extends > > the existing critical section to cover the entire loop body. > > > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > --- > > kernel/rcutree.c | 6 ++++-- > > 1 files changed, 4 insertions(+), 2 deletions(-) > > > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > > index 9f44749..fbe43b0 100644 > > --- a/kernel/rcutree.c > > +++ b/kernel/rcutree.c > > @@ -746,14 +746,16 @@ static void print_other_cpu_stall(struct rcu_state *rsp) > > rcu_for_each_leaf_node(rsp, rnp) { > > raw_spin_lock_irqsave(&rnp->lock, flags); > > ndetected += rcu_print_task_stall(rnp); > > - raw_spin_unlock_irqrestore(&rnp->lock, flags); > > - if (rnp->qsmask == 0) > > + if (rnp->qsmask == 0) { > > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > > continue; > > + } > > for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++) > > if (rnp->qsmask & (1UL << cpu)) { > > print_cpu_stall_info(rsp, rnp->grplo + cpu); > > ndetected++; > > } > > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > > } > > Now that you've extended the lock over the rest of the loop body, I > think this would look much clearer if written without the continue and > duplicate lock release: > > ... > if (rnp->qsmask != 0) > for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++) > .... > raw_spin_unlock_irqrestore(&rnp->lock, flags); > }
And my Hollerith experience strikes again! ;-)
Though this one seems more worthwhile, so I am making the change, conflicts permitting.
Thanx, Paul
| |