On Fri, Dec 28, 2012 at 12:35:43PM -0800, Tejun Heo wrote: > Instead of holding blkcg->lock while walking ->blkg_list and executing > prfill(), RCU walk ->blkg_list and hold the blkg's queue lock while > executing prfill(). This makes prfill() implementations easier as > stats are mostly protected by queue lock. > > This will be used to implement hierarchical stats. >
Hi Tejun, I think dropping blkcg->lock might be a problem. Using RCU we have made sure that blkg and q are around. But what about blkg->q.backing_dev_info.dev. We can follow bdi->dev pointer in blkg_dev_name(). I am not sure if we ever clear it from q or not when device goes away. Thanks Vivek > Signed-off-by: Tejun Heo <[email protected]> > --- > block/blk-cgroup.c | 14 +++++++++----- > 1 file changed, 9 insertions(+), 5 deletions(-) > > diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c > index a1a4b97..22f75d1 100644 > --- a/block/blk-cgroup.c > +++ b/block/blk-cgroup.c > @@ -504,8 +504,9 @@ static const char *blkg_dev_name(struct blkcg_gq *blkg) > * > * This function invokes @prfill on each blkg of @blkcg if pd for the > * policy specified by @pol exists. @prfill is invoked with @sf, the > - * policy data and @data. If @show_total is %true, the sum of the return > - * values from @prfill is printed with "Total" label at the end. > + * policy data and @data and the matching queue lock held. If @show_total > + * is %true, the sum of the return values from @prfill is printed with > + * "Total" label at the end. > * > * This is to be used to construct print functions for > * cftype->read_seq_string method. > @@ -520,11 +521,14 @@ void blkcg_print_blkgs(struct seq_file *sf, struct > blkcg *blkcg, > struct hlist_node *n; > u64 total = 0; > > - spin_lock_irq(&blkcg->lock); > - hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) > + rcu_read_lock(); > + hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) { > + spin_lock_irq(blkg->q->queue_lock); > if (blkcg_policy_enabled(blkg->q, pol)) > total += prfill(sf, blkg->pd[pol->plid], data); > - spin_unlock_irq(&blkcg->lock); > + spin_unlock_irq(blkg->q->queue_lock); > + } > + rcu_read_unlock(); > > if (show_total) > seq_printf(sf, "Total %llu\n", (unsigned long long)total); > -- > 1.8.0.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
