From 72e06c255181537d0b3e1f657a9ed81655d745b1 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 5 Mar 2012 13:15:00 -0800 Subject: blkcg: shoot down blkio_groups on elevator switch Elevator switch may involve changes to blkcg policies. Implement shoot down of blkio_groups. Combined with the previous bypass updates, the end goal is updating blkcg core such that it can ensure that blkcg's being affected become quiescent and don't have any per-blkg data hanging around before commencing any policy updates. Until queues are made aware of the policies that applies to them, as an interim step, all per-policy blkg data will be shot down. * blk-throtl doesn't need this change as it can't be disabled for a live queue; however, update it anyway as the scheduled blkg unification requires this behavior change. This means that blk-throtl configuration will be unnecessarily lost over elevator switch. This oddity will be removed after blkcg learns to associate individual policies with request_queues. * blk-throtl dosen't shoot down root_tg. This is to ease transition. Unified blkg will always have persistent root group and not shooting down root_tg for now eases transition to that point by avoiding having to update td->root_tg and is safe as blk-throtl can never be disabled -v2: Vivek pointed out that group list is not guaranteed to be empty on return from clear function if it raced cgroup removal and lost. Fix it by waiting a bit and retrying. This kludge will soon be removed once locking is updated such that blkg is never in limbo state between blkcg and request_queue locks. blk-throtl no longer shoots down root_tg to avoid breaking td->root_tg. Also, Nest queue_lock inside blkio_list_lock not the other way around to avoid introduce possible deadlock via blkcg lock. -v3: blkcg_clear_queue() repositioned and renamed to blkg_destroy_all() to increase consistency with later changes. cfq_clear_queue() updated to check q->elevator before dereferencing it to avoid NULL dereference on not fully initialized queues (used by later change). Signed-off-by: Tejun Heo Cc: Vivek Goyal Signed-off-by: Jens Axboe --- block/cfq-iosched.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) (limited to 'block/cfq-iosched.c') diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 72680a6..61693d3 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1225,10 +1225,11 @@ static void cfq_destroy_cfqg(struct cfq_data *cfqd, struct cfq_group *cfqg) cfq_put_cfqg(cfqg); } -static void cfq_release_cfq_groups(struct cfq_data *cfqd) +static bool cfq_release_cfq_groups(struct cfq_data *cfqd) { struct hlist_node *pos, *n; struct cfq_group *cfqg; + bool empty = true; hlist_for_each_entry_safe(cfqg, pos, n, &cfqd->cfqg_list, cfqd_node) { /* @@ -1238,7 +1239,10 @@ static void cfq_release_cfq_groups(struct cfq_data *cfqd) */ if (!cfq_blkiocg_del_blkio_group(&cfqg->blkg)) cfq_destroy_cfqg(cfqd, cfqg); + else + empty = false; } + return empty; } /* @@ -1265,6 +1269,19 @@ static void cfq_unlink_blkio_group(void *key, struct blkio_group *blkg) spin_unlock_irqrestore(cfqd->queue->queue_lock, flags); } +static struct elevator_type iosched_cfq; + +static bool cfq_clear_queue(struct request_queue *q) +{ + lockdep_assert_held(q->queue_lock); + + /* shoot down blkgs iff the current elevator is cfq */ + if (!q->elevator || q->elevator->type != &iosched_cfq) + return true; + + return cfq_release_cfq_groups(q->elevator->elevator_data); +} + #else /* GROUP_IOSCHED */ static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd) { @@ -3875,6 +3892,7 @@ static struct elevator_type iosched_cfq = { static struct blkio_policy_type blkio_policy_cfq = { .ops = { .blkio_unlink_group_fn = cfq_unlink_blkio_group, + .blkio_clear_queue_fn = cfq_clear_queue, .blkio_update_group_weight_fn = cfq_update_blkio_group_weight, }, .plid = BLKIO_POLICY_PROP, -- cgit v1.1