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);
}
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