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" <paul...@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 <paul...@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
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