| Date | Fri, 31 Aug 2012 11:23:02 -0700 | From | Josh Triplett <> | Subject | Re: [PATCH tip/core/rcu 10/15] rcu: Protect rcu_node accesses during CPU stall warnings |
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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); }
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